View source for Glossary of aerospace engineering

{{Short description|List of definitions of terms and concepts commonly used in aerospace engineering}}
This glossary of '''aerospace engineering terms''' pertains specifically to '''[[aerospace engineering]]''', its sub-disciplines, and related fields including [[aviation]] and [[aeronautics]]. For a broad overview of engineering, see [[glossary of engineering]].

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== A ==

* '''[[Height above ground level|Above ground level]]''' – In [[aviation]], [[atmospheric sciences]] and [[broadcasting]], a '''height above ground level''' ('''AGL'''<ref name="CAP413">{{cite book | date=28 May 2015 | title=Radiotelephony Manual |publisher=UK Civil Aviation Authority| id=CAP413| isbn=9780-11792-893-0}}</ref>) is a [[height#In aviation|height]] measured with respect to the underlying [[earth's surface|ground surface]]. This is as opposed to altitude/elevation [[above mean sea level]] (AMSL), or (in [[broadcast engineering]]) [[height above average terrain]] (HAAT). In other words, these expressions (AGL, AMSL, HAAT) indicate where the "zero level" or "reference altitude" is located.
* '''[[Absolute humidity]]''' – describes the water content of air and is expressed in either grams per cubic meter<ref>Wyer, S.S., "A treatise on producer-gas and gas-producers", (1906) The Engineering and Mining Journal, London, p.23</ref> or grams per kilogram.<ref>Perry, R.H. and Green, D.W, (2007) ''[[Perry's Chemical Engineers' Handbook]]'' (8th Edition), Section 12, Psychrometry, Evaporative Cooling and Solids Drying [[McGraw-Hill]], {{ISBN|978-0-07-151135-3}}</ref>
* '''[[Absolute value]]''' – In [[mathematics]], the absolute value or '''modulus''' {{math|{{!}}''x''{{!}}}} of a [[real number]]&nbsp;{{mvar|x}} is the [[non-negative]] value of&nbsp;{{mvar|x}} without regard to its [[sign (mathematics)|sign]]. Namely, {{math|1={{!}}''x''{{!}} = ''x''}} for a [[positive number|positive]]&nbsp;{{mvar|x}}, {{math|1={{!}}''x''{{!}} = −''x''}} for a [[negative number|negative]]&nbsp;{{mvar|x}} (in which case {{math|−''x''}} is positive), and {{math|1={{!}}0{{!}} = 0}}. For example, the absolute value of 3 is 3, and the absolute value of −3 is also 3. The absolute value of a number may be thought of as its [[distance]] from zero.
* '''[[Acceleration]]''' – In [[physics]], acceleration is the [[Rate (mathematics)|rate]] of change of [[velocity]] of an object with respect to time. An object's acceleration is the net result of any and all [[force]]s acting on the object, as described by [[Newton's Second Law]].<ref>{{cite book |title=The Principles of Mechanics |first=Henry |last=Crew |publisher=BiblioBazaar, LLC |year=2008 |isbn=978-0-559-36871-4 |pages=43}}</ref> The [[International System of Units|SI]] unit for acceleration is [[metre per second squared]] {{nowrap|(m s<sup>−2</sup>).}} Accelerations are [[Euclidean vector|vector]] quantities (they have [[Magnitude (mathematics)|magnitude]] and [[Direction (geometry)|direction]]) and add according to the [[parallelogram law]].<ref>{{cite book |title=Relativity and Common Sense |first=Hermann |last=Bondi |pages=[https://archive.org/details/relativitycommon0000bond/page/3 3] |publisher=Courier Dover Publications |year=1980 |isbn=978-0-486-24021-3 |url=https://archive.org/details/relativitycommon0000bond/page/3 }}</ref><ref>{{cite book |title=Physics the Easy Way |pages=[https://archive.org/details/physicseasyway00lehr_0/page/27 27] |first=Robert L. |last=Lehrman |publisher=Barron's Educational Series |year=1998 |isbn=978-0-7641-0236-3 |url=https://archive.org/details/physicseasyway00lehr_0/page/27 }}</ref> As a [[Vector space|vector]], the calculated net [[force]] is equal to the product of the object's mass (a [[Scalar (physics)|scalar]] quantity) and its acceleration.
* '''[[Acquisition of signal]]''' – A '''pass''', in [[spaceflight]] and [[satellite communications]], is the period in which a [[satellite]] or other [[spacecraft]] is above the [[Horizontal coordinate system|local horizon]] and available for [[radio]] communication with a particular [[ground station]], [[satellite receiver]], or relay satellite (or, in some cases, for visual sighting). The beginning of a pass is termed ''acquisition of signal''; the end of a pass is termed ''loss of signal''.<ref name="NLSA">{{cite web|title=AOS, TCA, and LOS|url=http://www.nlsa.com/definitions/aos_defined.html|publisher=Northern Lights Software Associates|access-date=17 November 2015}}</ref> The point at which a spacecraft comes closest to a ground observer is the ''time of closest approach''.<ref name="NLSA" />
* '''[[Action (physics)|Action]]''' – In [[physics]], action is an attribute of the [[dynamics (physics)|dynamics]] of a [[physical system]] from which the [[equations of motion]] of the system can be derived. It is a [[functional (mathematics)|mathematical functional]] which takes the [[trajectory]], also called ''path'' or ''history'', of the system as its argument and has a [[real number]] as its result. Generally, the action takes different values for different paths.<ref name="mcgraw1">McGraw Hill Encyclopaedia of Physics (2nd Edition), C.B. Parker, 1994, {{ISBN|0-07-051400-3}}</ref> Action has the [[dimensional analysis|dimensions]] of [[energy|[energy]]]&sdot;[[time|[time]]] or [[momentum|[momentum]]]&sdot;[[length|[length]]], and its [[SI unit]] is [[joule]]-second.
* '''[[Automatic direction finder|ADF]]''' – Automatic direction finder
* '''[[Advanced Space Vision System]]''' – The Advanced Space Vision System (also known as the Space Vision System or by its acronym SVS) is a [[computer vision]] system designed primarily for [[International Space Station]] (ISS) assembly.<ref name="nrcc">{{Cite web|url=http://www.nrc-cnrc.gc.ca/eng/education/innovations/discoveries/svs.html|title=Space Vision System Helps Astronauts See in Space|access-date=February 13, 2008|publisher=National Research Council of Canada|year=2008|author=NRCC|url-status=dead|archive-url=https://web.archive.org/web/20080603143525/http://www.nrc-cnrc.gc.ca/eng/education/innovations/discoveries/svs.html|archive-date=June 3, 2008}}</ref> The system uses regular 2D cameras in the [[Space Shuttle]] bay, on the [[Canadarm]], or on the ISS along with cooperative targets to calculate the 3D position of an object.<ref name="nrcc" />
* '''[[Aeroacoustics]]''' – is a branch of [[acoustics]] that studies noise generation via either [[turbulent]] fluid motion or [[aerodynamic]] forces interacting with surfaces. Noise generation can also be associated with periodically varying flows.  A notable example of this phenomenon is the [[Aeolian sound|Aeolian tones]] produced by wind blowing over fixed objects.
* '''[[Aerobraking]]''' – is a [[spaceflight]] maneuver that reduces the high point of an [[elliptical orbit]] ([[apoapsis]]) by flying the vehicle through the [[atmosphere]] at the low point of the [[orbit]] ([[periapsis]]). The resulting [[Drag (physics)|drag]] slows the [[spacecraft]]. Aerobraking is used when a spacecraft requires a low orbit after arriving at a body with an atmosphere, and it requires less fuel than does the direct use of a [[rocket engine]].
* '''[[Aerocapture]]''' – is an [[Orbital maneuver|orbital transfer maneuver]] used to reduce the velocity of a spacecraft from a [[hyperbolic trajectory]] to an elliptical orbit around the targeted celestial body.
* '''[[Aerodynamics]]''' – is the study of the motion of [[air]], particularly with respect to its interaction with a solid object, such as an [[airplane]] wing. Aerodynamics is a sub-field of [[gas dynamics]], which in turn is a sub-field of [[fluid dynamics]]. Many aspects and principles of aerodynamics theory are common to these three fields.
* '''[[Aeroelasticity]]''' – is the branch of [[physics]] and [[engineering]] that studies the interactions between the [[inertial force|inertial]], [[elasticity (physics)|elastic]], and [[aerodynamic force|aerodynamic]] forces that occur when an elastic body is exposed to a [[fluid]] flow. Although historical studies have been focused on aeronautical applications, recent research has found applications in fields such as [[energy harvesting]]<ref>{{cite journal|last=Sousa|first=V. C.|title=Enhanced aeroelastic energy harvesting by exploiting combined nonlinearities: theory and experiment|journal=Smart Materials and Structures|year=2011|volume=20|number=9|pages=094007|doi=10.1088/0964-1726/20/9/094007|bibcode=2011SMaS...20i4007S|s2cid=67767510 |doi-access=free}}</ref> and understanding [[snoring]].<ref>{{cite journal|last=Ellis|first= P. D. M. |title= Laser palatoplasty for snoring due to palatal flutter: a further report|journal= Clinical Otolaryngology|year=1994|volume=19|number=4|pages= 350–1 |doi= 10.1111/j.1365-2273.1994.tb01245.x |pmid= 7994895 }}</ref> The study of aeroelasticity may be broadly classified into two fields: static aeroelasticity, which deals with the static or [[steady state|steady]] response of an elastic body to a fluid flow; and dynamic aeroelasticity, which deals with the body's [[Dynamics (mechanics)|dynamic]] (typically [[vibration]]al) response. Aeroelasticity draws on the study of [[fluid mechanics]], [[solid mechanics]], [[structural dynamics]] and [[dynamical systems]]. The synthesis of aeroelasticity with [[thermodynamics]] is known as aerothermoelasticity, and its synthesis with [[control theory]] is known as aeroservoelasticity.
* '''[[Aeronautics]]''' – is the science or art involved with the study, [[design process|design]], and manufacturing of air [[flight]] capable machines, and the techniques of operating [[aircraft]] and rockets within the [[atmosphere]].<ref>{{Cite web |last=Entropol |title=Definition of Aeronautics |url=https://www.spacedictionary.com/aeronautics |access-date=2023-06-24 |website=www.spacedictionary.com |language=en}}</ref>
* '''[[Aerospace architecture]]''' – is broadly defined to encompass [[architecture|architectural]] design of non-habitable and habitable structures and living and working environments in aerospace-related facilities, habitats, and vehicles. These environments include, but are not limited to: science platform aircraft and aircraft-deployable systems; [[space vehicle]]s, [[space station]]s, habitats and lunar and [[planetary surface construction]] bases; and Earth-based control, experiment, launch, logistics, payload, simulation and test facilities. Earth analogs to space applications may include Antarctic, desert, high altitude, underground, undersea environments and closed ecological systems.
* '''[[Aerospace bearing]]''' – Aerospace bearings are the bearings installed in [[aircraft]] and [[aerospace]] systems including commercial, private, military, or space applications.
* '''[[Aerospace engineering]]''' – is the primary field of [[engineering]] concerned with the development of [[aircraft]] and [[spacecraft]].<ref>''Encyclopedia of Aerospace Engineering''. [[John Wiley & Sons]], 2010. {{ISBN|978-0-470-75440-5}}.</ref> It has two major and overlapping branches: Aeronautical engineering and Astronautical Engineering.  [[Avionics]] engineering is similar, but deals with the [[electronic engineering|electronics]] side of aerospace engineering.
* '''[[Aerospace materials]]''' – are materials, frequently [[alloy|metal alloy]]s, that have either been developed for, or have come to prominence through, their use for [[aerospace]] purposes. These uses often require exceptional performance, strength or heat resistance, even at the cost of considerable expense in their production or machining. Others are chosen for their long-term reliability in this safety-conscious field, particularly for their resistance to [[fatigue (material)|fatigue]].
* '''[[Aerospike engine]]''' – is a type of [[rocket engine]] that maintains its [[aerodynamic]] efficiency across a wide range of [[altitude]]s. It belongs to the class of [[altitude compensating nozzle]] engines. A vehicle with an aerospike engine uses 25–30% less fuel at low altitudes, where most missions have the greatest need for [[thrust]].
* '''[[Aerostat]]''' – is a [[lighter than air]] aircraft that gains its lift through the use of a buoyant gas. Aerostats include unpowered [[balloon (aircraft)|balloons]] and powered [[airship]]s.
* '''[[Aerostructure]]''' – is a component of an [[aircraft]]'s airframe. This may include all or part of the [[fuselage]], [[wing]]s, or flight control surfaces.
* '''[[Aft-crossing trajectory]]''' – is an alternate flight path for a rocket. The rocket's rotation (induced by the deployment from the aircraft) is slowed by a small [[parachute]] attached to its tail, then ignited once the carrier aircraft has passed it.  It is ignited before it is pointing fully vertically, however it will turn to do so, and accelerates to pass behind the carrier aircraft.
* '''[[Above ground level|AGL]]''' – Above ground level
* '''[[Aileron]]''' – is a hinged [[flight control surface]] usually forming part of the [[trailing edge]] of each [[wing]] of a [[fixed-wing aircraft]]. Ailerons are used in pairs to control the aircraft in [[Flight dynamics|roll]] (or movement around the aircraft's [[Flight control surfaces#Longitudinal axis|longitudinal axis]]), which normally results in a change in flight path due to the tilting of the [[Lift (force)|lift vector]].  Movement around this axis is called 'rolling' or 'banking'.
* '''[[Air-augmented rocket]]''' – 
* '''[[Aircraft]]''' – is a [[machine]] that is able to [[flight|fly]] by gaining support from the [[air]].<!-- English word "aircraft" is singular and plural with no "s". See also the link to Wiktionary below. --> It counters the force of gravity by using either [[Buoyancy|static lift]] or by using the [[Lift (force)|dynamic lift]] of an [[airfoil]],<ref>{{cite web|url=http://dictionary.reference.com/browse/aircraft|title=Aircraft - Define Aircraft at Dictionary.com|work=Dictionary.com|access-date=1 April 2015|url-status=live|archive-url=https://web.archive.org/web/20150328141634/http://dictionary.reference.com/browse/aircraft|archive-date=28 March 2015|df=dmy-all}}</ref> or in a few cases the [[Powered lift|downward thrust]] from [[jet engine]]s.  Common examples of aircraft include [[airplane]]s, [[helicopter]]s, [[airship]]s (including [[blimp]]s), [[Glider (aircraft)|glider]]s, and [[hot air balloon]]s.<ref name="wingsoverkansas">{{cite web|title=Different Kinds & Types of Aircraft|url=http://www.wingsoverkansas.com/features/a1037/|website=www.wingsoverkansas.com|url-status=live|archive-url=https://web.archive.org/web/20161121165354/http://www.wingsoverkansas.com/features/a1037/|archive-date=21 November 2016|df=dmy-all}}</ref>
* '''[[Aircraft flight control systems]]''' – A conventional [[Fixed-wing aircraft|fixed-wing]] '''aircraft flight control system''' consists of [[flight control surfaces]], the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight. [[Aircraft engine controls]] are also considered as flight controls as they change speed.
* '''[[Aircraft flight mechanics]]''' – 
* '''[[Airfoil]]''' – An airfoil ([[American English]]) or '''aerofoil''' ([[British English]]) is the cross-sectional shape of a [[wing]], blade (of a [[Propeller (aeronautics)|propeller]], [[Helicopter rotor|rotor]], or [[turbine]]), or [[sail]] (as seen in [[Multiview orthographic projection#Section|cross-section]]).
* '''[[Airlock]]''' – is a device which permits the passage of people and objects between a [[pressure vessel]] and its surroundings while minimizing the change of [[pressure]] in the vessel and loss of [[air]] from it.  The lock consists of a small chamber with two [[Hermetic seal|airtight]] [[door]]s in series which do not open simultaneously.
* '''[[Airship]]''' – An airship or '''dirigible balloon''' is a type of [[aerostat]] or lighter-than-air aircraft that can navigate through the air under its own power.<ref>{{cite web|url=http://www.merriam-webster.com/dictionary/airship|title=Definition of AIRSHIP|work=merriam-webster.com|access-date=4 October 2016}}</ref> Aerostats gain their lift from large gas bags filled with a [[lifting gas]] that is less dense than the surrounding air.
* '''[[Albedo]]''' – is the measure of the [[diffuse reflection]] of [[sunlight|solar radiation]] out of the total [[solar radiation]] received by an [[astronomical body]] (e.g. a [[planet]] like [[Earth]]). It is [[dimensionless number|dimensionless]] and measured on a scale from 0 (corresponding to a [[black body]] that absorbs all incident radiation) to 1 (corresponding to a body that reflects all incident radiation).
* '''[[Anemometer]]''' – is a device used for measuring [[wind speed]], and is also a common [[weather station]] instrument.<ref>{{Cite web |last=Entropol |title=Definition of Anemometer |url=https://www.spacedictionary.com/anemometer |access-date=2023-06-24 |website=www.spacedictionary.com |language=en}}</ref> The term is derived from the Greek word ''anemos'', which means [[wind]], and is used to describe any wind speed instrument used in [[meteorology]].
* '''[[Angle of attack]]''' – In [[fluid dynamics]], angle of attack ('''AOA''', or '''<math>\alpha</math>''') is the [[angle]] between a [[Airfoil#Airfoil terminology|reference line]] on a body (often the [[chord (aircraft)|chord line]] of an [[airfoil]]) and the [[vector (geometry)|vector]] representing the relative motion between the body and the fluid through which it is moving.<ref name="nasa">{{cite web|url=http://www.grc.nasa.gov/WWW/k-12/airplane/incline.html|title=NASA aeronautics guided tour}}</ref> Angle of attack is the angle between the body's reference line and the oncoming flow.
* '''[[Angular momentum]]''' – In [[physics]], angular momentum (rarely, '''moment of momentum''' or '''rotational momentum''') is the rotational equivalent of [[linear momentum]]. It is an important quantity in physics because it is a [[Conservation law|conserved quantity]]—the total angular momentum of a system remains constant unless acted on by an external [[torque]].
* '''[[Angular velocity]]''' – In [[physics]], the angular velocity of a particle is the rate at which it rotates around a chosen center point: that is, the time rate of change of its [[angular displacement]] relative to the origin (i.e. in layman's terms: how quickly an object goes around something over a period of time – e.g. how fast the earth orbits the sun). It is measured in angle per unit time, [[radians per second]] in [[SI]] units, and is usually represented by the symbol [[omega]] ('''ω''', sometimes '''Ω'''). By convention, positive angular velocity indicates counter-clockwise rotation, while negative is clockwise.
* '''[[Anticyclone]]''' – An anticyclone (that is, opposite to a [[cyclone]]) is a [[weather]] [[meteorological phenomenon|phenomenon]] defined by the United States [[National Weather Service]]'s glossary as "a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere".<ref>{{cite web|title=Glossary: Anticyclone|publisher=National Weather Service|access-date=January 19, 2010|url=http://www.nws.noaa.gov/glossary/index.php?word=anticyclone|url-status=live|archive-url=https://web.archive.org/web/20110629140523/http://www.nws.noaa.gov/glossary/index.php?word=anticyclone|archive-date=June 29, 2011}}</ref>
* '''[[Antimatter rocket]]''' – is a proposed class of [[rocket]]s that use [[antimatter]] as their power source. There are several designs that attempt to accomplish this goal. The advantage to this class of rocket is that a large fraction of the [[rest mass]] of a matter/antimatter mixture may be converted to energy, allowing antimatter rockets to have a far higher [[energy density]] and [[specific impulse]] than any other proposed class of rocket.
* '''[[Apsis]]''' – is an extreme point in the [[orbit]] of an [[physical body|object]]. The word comes via Latin from Greek and is [[cognate]] with ''[[apse]]''.<ref name=":0">{{cite web|url=http://dictionary.reference.com/browse/apsis|title=the definition of apsis|website=Dictionary.com}}</ref> For [[elliptic orbit]]s about a larger body, there are two apsides, named with the prefixes ''peri-'' ({{ety||''περί'' (peri)|near}}) and ''ap-''/''apo-'' ({{ety||''ἀπ(ό)'' (ap(ó))|away from}}) added to a reference to the [[primary (astronomy)|body being orbited]].
* '''[[Arcjet rocket]]''' – or '''arcjet thruster''' is a form of [[electrically powered spacecraft propulsion]], in which an electrical discharge (arc) is created in a flow of propellant<ref>John, R. R., Bennett, S., and Connors, J. P., "Arcjet Engine Performance: Experiment and Theory," ''AIAA Journal, Vol. 1,'' No. 11, Nov. 1963. [http://arc.aiaa.org/doi/pdf/10.2514/3.2103 http://arc.aiaa.org/doi/pdf/10.2514/3.2103] {{Webarchive|url=https://web.archive.org/web/20181129183913/https://arc.aiaa.org/doi/pdf/10.2514/3.2103 |date=2018-11-29 }}</ref><ref>Wallner, Lewis E. and Czika, Joseph, Jr, ''[https://web.archive.org/web/20140909035419/http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA392837 ARC-Jet Thrustor for Space Propulsion],'' NASA Technical note TN D-2868, NASA Lewis Research Center, June 1965 (accessed September 8, 2014)</ref> (typically [[hydrazine]] or [[ammonia]]).  This imparts additional energy to the propellant, so that one can extract more work out of each kilogram of propellant, at the expense of increased power consumption and (usually) higher cost.  Also, the [[thrust]] levels available from typically used arcjet engines are very low compared with chemical engines.
* '''[[Areal velocity]]''' – In [[classical mechanics]], areal velocity (also called '''sector velocity''' or '''sectorial velocity''') is the rate at which [[area]] is swept out by a particle as it moves along a [[curve]].
* '''[[Argument of periapsis]]''' – (also called '''argument of perifocus''' or '''argument of pericenter'''), symbolized as ''ω'', is one of the [[orbital element]]s of an [[orbit]]ing body.  Parametrically, ''ω'' is the angle from the body's [[ascending node]] to its [[periapsis]], measured in the direction of motion.
* '''[[ARP4761]]''' – 
* '''[[Aspect ratio (aeronautics)]]''' – In [[aeronautics]], the aspect ratio of a [[wing]] is the ratio of its [[Wingspan|span]] to its mean [[chord (aircraft)|chord]]. It is equal to the square of the wingspan divided by the wing area. Thus, a long, narrow wing has a high aspect ratio, whereas a short, wide wing has a low aspect ratio.<ref name="Kermode">Kermode, A.C. (1972), ''Mechanics of Flight'', Chapter 3, (p.103, eighth edition), Pitman Publishing Limited, London {{ISBN|0-273-31623-0}}</ref> Aspect ratio and other features of the [[Planform (aeronautics)|planform]] are often used to predict the aerodynamic efficiency of a wing because the [[lift-to-drag ratio]] increases with aspect ratio, improving [[fuel economy in aircraft]].
* '''[[Asteroid]]''' – Asteroids are [[minor planet]]s, especially of the [[Solar System#Inner solar system|inner Solar System]]. Larger asteroids <!-- greater than what size? -->have also been called '''planetoids'''. These terms have historically been applied to any astronomical object orbiting the [[Sun]] that did not resemble a planet-like disc and was not observed to have characteristics of an active [[comet]] such as a tail. As [[Distant minor planet|minor planets in the outer Solar System]] were discovered they were typically found to have [[Volatile (astrogeology)|volatile]]-rich surfaces similar to comets. As a result, they were often distinguished from objects found in the main [[asteroid belt]].<ref>{{cite web |url=http://ssd.jpl.nasa.gov/?asteroids |title=Asteroids |website=NASA – Jet Propulsion Laboratory |access-date=13 September 2010}}</ref>
* '''[[Astrodynamics]]''' – '''Orbital mechanics''' or astrodynamics is the application of [[ballistics]] and [[celestial mechanics]] to the practical problems concerning the motion of [[rocket]]s and other [[spacecraft]].
* '''[[Atmospheric entry]]''' – is the movement of an object from [[outer space]] into and through the gases of an [[atmosphere]] of a [[planet]], [[dwarf planet]] or [[natural satellite]]. There are two main types of atmospheric entry: uncontrolled entry, such as the entry of [[astronomical object]]s, [[space debris]] or [[bolide]]s; and controlled entry (or reentry) of a spacecraft capable of being navigated or following a predetermined course. Technologies and procedures allowing the controlled atmospheric '''entry, descent and landing''' of spacecraft are collectively termed as '''EDL'''.
* '''[[Spacecraft attitude control|Attitude control]]''' – is controlling the orientation of an object with respect to an [[inertial frame of reference]] or another entity like the [[celestial sphere]], certain fields, and nearby objects, etc. Controlling vehicle attitude requires [[sensors]] to measure vehicle orientation, [[actuators]] to apply the torques needed to re-orient the vehicle to a desired attitude, and [[algorithms]] to command the actuators based on (1) sensor measurements of the current attitude and (2) specification of a desired attitude. The integrated field that studies the combination of sensors, actuators and algorithms is called "Guidance, Navigation and Control" (GNC).
* '''[[Radio direction finder#Automatic direction finder (ADF)|Automatic direction finder]]''' – ('''ADF''') is a marine or aircraft radio-navigation instrument that automatically and continuously displays the relative bearing from the ship or aircraft to a suitable radio station.<ref>{{cite book | author=Federal Aviation Administration | year=2008 | chapter=Chapter 15: Navigation | title=Pilot's Handbook of Aeronautical Knowledge | publisher=US Dept. of Transportation | chapter-url=https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2015.pdf | isbn=978-1-56027-783-5 | access-date=14 September 2015 | url-status=dead | url=http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2015.pdf | archive-url=https://web.archive.org/web/20150618215425/http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2015.pdf | archive-date=18 June 2015 }}</ref><ref>{{cite web | author=Civil Aviation Safety Authority | year=2005 | url=http://www.casa.gov.au/pilots/download/NDB.pdf | title=Operational Notes on Non-Directional Beacons (NDB) and Associated Automatic Direction Finding (ADF) | publisher=Government of Australia | access-date=11 February 2011 | url-status=dead | archive-url=https://web.archive.org/web/20090530151806/http://www.casa.gov.au/pilots/download/NDB.pdf | archive-date=30 May 2009 }}</ref>
* '''[[Avionics]]''' – are the [[Electronics|electronic]] systems used on aircraft, [[artificial satellite]]s, and [[spacecraft]]. Avionic systems include communications, navigation, the display and management of multiple systems, and the hundreds of systems that are fitted to aircraft to perform individual functions.
* '''[[Axial stress]]''' – a normal stress parallel to the axis of cylindrical symmetry.

== B ==

* '''[[Balloon (aeronautics)|Balloon]]''' – In [[aeronautics]], a balloon is an unpowered [[aerostat]], which remains aloft or floats due to its [[buoyancy]]. A balloon may be free, moving with the wind, or [[Moored balloon|tethered]] to a fixed point. It is distinct from an [[airship]], which is a powered [[aerostat]] that can propel itself through the air in a controlled manner.
* '''[[Ballute]]''' – (a [[portmanteau]] of ''[[balloon]]'' and ''[[parachute]]'') is a parachute-like braking device optimized for use at high altitudes and [[supersonic]] velocities. Invented by [[Goodyear Tire and Rubber Company|Goodyear]] in 1958, the original ballute was a cone-shaped balloon with a [[toroid]]al burble fence fitted around its widest point. A burble fence is an inflated structure intended to ensure [[flow separation]].<ref>{{cite report|title=Development of Ballute / for Retardation of ARCAS Rocketsondes|url=https://apps.dtic.mil/sti/pdfs/AD0625785.pdf|date=December 1965|first=J.J. |last=Graham, Jr|access-date=November 16, 2022}}</ref>

This stabilizes the ballute as it decelerates through different flow regimes (from supersonic to subsonic).
* '''[[Beam-powered propulsion]]''' – also known as directed energy propulsion, is a class of [[aircraft]] or [[spacecraft propulsion]] that uses energy beamed to the spacecraft from a remote power plant to provide energy. The beam is typically either a [[microwave]] or a [[laser]] beam and it is either pulsed or continuous.  A continuous beam lends itself to [[thermal rocket]]s, photonic thrusters and [[light sail]]s, whereas a pulsed beam lends itself to ablative thrusters and [[pulse detonation engine]]s.<ref>{{Citation|last=Breakthrough|title=Progress in beamed energy propulsion {{!}} Kevin Parkin|date=2018-05-29|url=https://www.youtube.com/watch?v=gnvHNoYuTpI|access-date=2018-06-07}}</ref>
* '''[[Bearing (navigation)|Bearing]]''' – In [[navigation]], bearing is the horizontal angle between the direction of an object and another object, or between it and that of true north. ''Absolute bearing'' refers to the angle between the magnetic North (magnetic bearing) or true North (true bearing) and an object. For example, an object to the East would have an absolute bearing of 90 degrees. ''Relative bearing'' refers to the angle between the craft's forward direction, and the location of another object. For example, an object relative bearing of 0 degrees would be dead ahead; an object relative bearing 180 degrees would be behind.<ref>Rutstrum, Carl, ''The Wilderness Route Finder'', University of Minnesota Press (2000), {{ISBN|0-8166-3661-3}}, p. 194</ref> Bearings can be measured in [[Angular mil|mils]] or degrees.
* '''[[Bernoulli's principle]]''' – In [[fluid dynamics]], Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in [[pressure]] or a decrease in the [[fluid]]'s [[potential energy]].<ref name="Clancy1975">{{cite book|last=Clancy|first=L. J. |author-link=Laurence Joseph Clancy|title=Aerodynamics|url=https://books.google.com/books?id=zaNTAAAAMAAJ|year=1975|publisher=Wiley|isbn=978-0-470-15837-1}}</ref>{{rp|at=Ch.3}}<ref name="Batchelor2000">{{cite book|last=Batchelor|first=G. K. |author-link=George Batchelor|title=An Introduction to Fluid Dynamics|url=https://books.google.com/books?id=Rla7OihRvUgC&pg=PA156|year=2000|publisher=University Press|location=Cambridge |isbn=978-0-521-66396-0}}</ref>{{rp|at= § 3.5|pp=156–164}}
* '''[[Bi-elliptic transfer]]''' – is an [[orbital maneuver]] that moves a [[spacecraft]] from one [[orbit]] to another and may, in certain situations, require less [[delta-v]] than a [[Hohmann transfer orbit|Hohmann transfer]] maneuver. The bi-elliptic transfer consists of two half-[[elliptic orbit]]s. From the initial orbit, a first burn expends delta-v to boost the spacecraft into the first transfer orbit with an [[apoapsis]] at some point <math>r_b</math> away from the [[central body]]. At this point a second burn sends the spacecraft into the second elliptical orbit with [[periapsis]] at the radius of the final desired orbit, where a third burn is performed, injecting the spacecraft into the desired orbit.<ref name="Curtis">{{Cite book | last = Curtis | first = Howard | title = Orbital Mechanics for Engineering Students | page = 264 | publisher = [[Elsevier]] | year = 2005 | isbn = 0-7506-6169-0 | url = https://books.google.com/books?id=6aO9aGNBAgIC}}</ref>
* '''[[Big dumb booster]]''' – (BDB), is a general class of [[launch vehicle]] based on the premise that it is cheaper to operate large rockets of simple design than it is to operate smaller, more complex ones regardless of the lower payload efficiency.<ref name="mcd">Schnitt, Arthur (1998) [http://www.quarkweb.com/foyle/MinimumCostDesign.pdf ''Minimum Cost Design for Space Operations''.]</ref>
* '''[[Bleed air]]''' – produced by [[gas turbine]] engines is [[compressed air]] that is taken from the compressor stage of those engines, which is upstream of the fuel-burning sections.
* '''[[Booster (rocketry)|Booster]]''' – A booster [[rocket]] (or engine) is either the first stage of a [[multistage rocket|multistage]] [[launch vehicle]], or else a shorter-burning rocket used in parallel with longer-burning [[sustainer engine|sustainer rocket]]s to augment the [[space vehicle]]'s takeoff thrust and payload capability.<ref name="nasa-staging">{{Cite web |url=https://spaceflightsystems.grc.nasa.gov/education/rocket/rktstage.html |title=Rocket Staging |publisher=NASA |location=US |access-date=October 12, 2018 |archive-url=https://web.archive.org/web/20160602123849/https://spaceflightsystems.grc.nasa.gov/education/rocket/rktstage.html |archive-date=June 2, 2016 |url-status=dead }}</ref><ref>{{Cite web |url=https://www.nasa.gov/returntoflight/system/system_SRB.html |title=Solid Rocket Boosters |publisher=NASA |location=US |access-date=October 12, 2018 |archive-date=July 27, 2020 |archive-url=https://web.archive.org/web/20200727022348/https://www.nasa.gov/returntoflight/system/system_SRB.html |url-status=dead }}</ref>
* '''[[Boundary layer]]''' – In [[physics]] and [[fluid mechanics]], a boundary layer is an important concept and refers to the layer of [[fluid]] in the immediate vicinity of a [[Boundary (thermodynamic)|bounding surface]] where the effects of viscosity are significant. In the [[Earth's atmosphere]], the [[atmospheric boundary layer]] is the air layer near the ground affected by diurnal heat, moisture or momentum transfer to or from the surface.  On an [[aircraft]] [[wing]] the boundary layer is the part of the flow close to the wing, where [[viscosity|viscous]] [[force]]s distort the surrounding non-viscous flow.
* '''[[Buoyancy]]''' – In [[physics]], buoyancy or '''upthrust''', is an upward [[force]] exerted by a [[fluid]] that opposes the [[weight]] of an immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object. This pressure difference results in a net upwards force on the object. The magnitude of that force exerted is proportional to that pressure difference, and (as explained by [[Archimedes' principle]]) is equivalent to the weight of the fluid that would otherwise occupy the volume of the object, i.e. the [[Displacement (fluid)|displaced]] fluid.

== C ==

* '''[[Cabin pressurization]]''' – is a process in which conditioned air is pumped into the [[aircraft cabin|cabin]] of an aircraft or [[spacecraft]], in order to create a safe and comfortable environment for passengers and crew flying at high altitudes. For aircraft, this air is usually [[Bleed air|bled off]] from the [[gas turbine|gas turbine engines]] at the compressor stage, and for spacecraft, it is carried in high-pressure, often [[liquid oxygen|cryogenic]] tanks. The air is cooled, humidified, and mixed with recirculated air if necessary, before it is distributed to the cabin by one or more [[Environmental control system (aircraft)|environmental control systems]].<ref>{{cite web | url=http://blogs.howstuffworks.com/2011/04/12/how-airplane-cabin-pressurization-works-keeping-you-comfortable-in-the-death-zone-at-33000-feet/ | title=How Airplane Cabin Pressurization Works | publisher=How Stuff Works | date=April 12, 2011 | access-date=December 31, 2012 | author=Brain, Marshall | url-status=dead | archive-url=https://web.archive.org/web/20130115141028/http://blogs.howstuffworks.com/2011/04/12/how-airplane-cabin-pressurization-works-keeping-you-comfortable-in-the-death-zone-at-33000-feet/ | archive-date=January 15, 2013 }}</ref> The cabin pressure is regulated by the outflow valve.
* '''[[Cable lacing]]''' – is a method for tying [[Cable harness|wiring harness]]es and cable looms, traditionally used in [[telecommunication]], naval, and aerospace applications.  This old [[cable management]] technique, taught to generations of [[Lineman (technician)|linemen]],<ref name="popmech1905">{{citation|title=Cable Sewing Knots|journal=Popular Mechanics|date=May 1905|volume=7|number=5|issn=0032-4558|page=550|publisher=Hearst Magazines|url=https://books.google.com/books?id=oN8DAAAAMBAJ&pg=PA550|quote=Every lineman should know how to sew these knots.}}</ref> is still used in some modern applications since it does not create obstructions along the length of the cable, avoiding the handling problems of cables groomed by plastic or [[Hook-and-loop fastener|hook-and-loop]] [[cable tie]]s.
* '''[[Camber (aerodynamics)|Camber]]''' – the asymmetric curves on the top and bottom, or front and back, of an aerofoil
* '''[[Canard (aeronautics)|Canard]]''' – is an [[aeronautics|aeronautical]] arrangement wherein a small forewing or foreplane is placed forward of the main wing of a [[fixed-wing aircraft]].  The term "canard" may be used to describe the aircraft itself, the [[wing configuration]] or the foreplane.<ref>Wragg, D.; ''Historical Dictionary of Aviation'', History Press (2008), Page 79.</ref><ref>Clancy, L.; ''Aerodynamics'', Halsted (1975), Page 293.</ref><ref>{{citation |last=Crane |first=Dale |title=Dictionary of Aeronautical Terms |edition=3rd |page=86 |publisher=Aviation Supplies & Academics |year=1997 |isbn=978-1-56027-287-8}}.</ref>
* '''[[Centennial challenges]]''' – 
* '''[[Center of gravity]]''' – A body's center of gravity is the point around which the [[resultant force|resultant torque]] due to gravity forces vanishes. Where a gravity field can be considered to be uniform, the mass-center and the center-of-gravity will be the same. However, for satellites in orbit around a planet, in the absence of other torques being applied to a satellite, the slight variation (gradient) in gravitational field between closer-to (stronger) and further-from (weaker) the planet can lead to a torque that will tend to align the satellite such that its long axis is vertical. In such a case, it is important to make the distinction between the center-of-gravity and the mass-center. Any horizontal offset between the two will result in an applied torque.
* '''[[Center of mass]]''' – In [[physics]], the '''center of mass''' of a distribution of [[mass]] in space is the unique point where the [[weight function|weighted]] relative [[position (vector)|position]] of the distributed mass sums to zero, or the point where if a force is applied it moves in the direction of the force without rotating. The distribution of mass is balanced around the center of mass and the average of the weighted position coordinates of the distributed mass defines its coordinates.
* '''[[Center of pressure (fluid mechanics)|Center of pressure]]''' – is the point where the total sum of a [[pressure]] field acts on a body, causing a [[force]] to act through that point.
* '''[[Centrifugal compressor]]''' – '''Centrifugal compressors''', sometimes called '''radial compressors''', are a sub-class of dynamic axisymmetric work-absorbing [[turbomachinery]].<ref>Shepard, Dennis G. (1956). Principles of Turbomachinery. McMillan. {{ISBN|978-0-471-85546-0}}. LCCN 56002849.</ref> They achieve a pressure rise by adding [[kinetic energy]]/[[velocity]] to a continuous flow of [[fluid]] through the rotor or [[impeller]]. This kinetic energy is then converted to an increase in [[potential energy]]/static pressure by slowing the [[fluid dynamics|flow]] through a diffuser. The pressure rise in the impeller is in most cases almost equal to the rise in the diffuser.
* '''[[Chord (aeronautics)|Chord]]''' – is the imaginary straight line joining the leading and trailing edges of an [[aerofoil]].  The ''chord length'' is the distance between the [[trailing edge]] and the point on the leading edge where the chord intersects the [[leading edge]].<ref name="Clancy5">[[L. J. Clancy]] (1975), ''Aerodynamics'', Section 5.2, Pitman Publishing Limited, London. {{ISBN|0-273-01120-0}}</ref><ref>Houghton, E. L.; Carpenter, P.W. (2003). Butterworth Heinmann, ed. Aerodynamics for Engineering Students (5th ed.). {{ISBN|0-7506-5111-3}}. p.18</ref>
* '''[[Clean configuration]]''' – is the flight configuration of a [[fixed-wing aircraft]] when its external equipment is retracted to minimize drag and thus maximize [[airspeed]] for a given power setting.
* '''[[Cockpit]]''' – or '''flight deck''', is the area, usually near the front of an [[aircraft]] or [[spacecraft]], from which a [[Pilot in command|pilot]] controls the aircraft.
* '''[[Collimated beam]]''' – A '''collimated beam''' of [[light]] or other [[electromagnetic radiation]] has parallel [[ray (optics)|rays]], and therefore will spread minimally as it propagates. A perfectly collimated [[light beam]], with no [[beam divergence|divergence]], would not disperse with distance. Such a beam cannot be created, due to [[diffraction]].<ref>{{cite book |url=http://file.lasersaur.com/docs-thirdparty/Lasers.pdf |title=Melles Griot Catalog |chapter=Introduction to Laser Technology |author=<!-- Staff writer(s); no by-line --> |page=36.6 |date=n.d. |publisher=Melles Griot |access-date=25 August 2018}}</ref>
* '''[[Comet]]''' – is an icy, [[small Solar System body]] that, when passing close to the [[Sun]], warms and begins to release gases, a process called [[outgassing]]. This produces a visible atmosphere or [[Coma (cometary)|coma]], and sometimes also a [[Comet tail|tail]].
* '''[[Compressibility]]''' – In [[thermodynamics]] and [[fluid mechanics]], '''compressibility''' (also known as the coefficient of compressibility<ref>{{cite web|url=http://glossary.ametsoc.org/wiki/Coefficient_of_compressibility|title=Coefficient of compressibility - AMS Glossary|website=Glossary.AMetSoc.org|access-date=3 May 2017}}</ref> or isothermal compressibility<ref>{{cite web|url=http://petrowiki.org/Isothermal_compressibility_of_gases|title=Isothermal compressibility of gases -|website=Petrowiki.org|date=3 June 2015|access-date=3 May 2017}}</ref>) is a [[Measure (mathematics)|measure]] of the relative volume change of a [[fluid]] or [[solid]] as a response to a [[pressure]] (or mean [[stress (physics)|stress]]) change. In its simple form, the compressibility <math>\beta </math> may be expressed as
: <math>\beta=-\frac{1}{V}\frac{\partial V}{\partial p}</math>, where ''V'' is [[Volume (thermodynamics)|volume]] and ''p'' is pressure. The choice to define compressibility as the [[opposite (mathematics)|opposite]] of the fraction makes compressibility positive in the (usual) case that an increase in pressure induces a reduction in volume.  t is also known as reciprocal of bulk modulus(k) of elasticity of a fluid.
* '''[[Compression (physics)|Compression]]''' – In [[mechanics]], '''compression''' is the application of balanced inward ("pushing") forces to different points on a material or structure, that is, forces with no net sum or [[torque]] directed so as to reduce its size in one or more directions.<ref name="Beer">Ferdinand Pierre Beer, Elwood Russell Johnston, John T. DeWolf (1992), "Mechanics of Materials". (Book) McGraw-Hill Professional, {{ISBN|0-07-112939-1}}</ref> It is contrasted with [[tension (physics)|tension]] or traction, the application of balanced outward ("pulling") forces; and with [[shear stress|shearing]] forces, directed so as to displace layers of the material parallel to each other.  The [[compressive strength]] of materials and structures is an important engineering consideration.
* '''[[Compressor map]]''' – is a diagram showing significant performance parameters for a rotating compressor, and how they vary with changing ambient conditions of pressure and temperature.
* '''[[Computational fluid dynamics]]''' – ('''CFD'''), is a branch of [[fluid mechanics]] that uses [[numerical analysis]] and [[data structure]]s to analyze and solve problems that involve [[fluid dynamics|fluid flows]].  Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid ([[liquid]]s and [[gas]]es) with surfaces defined by [[Boundary value problem#Boundary value conditions|boundary conditions]]. With high-speed [[supercomputer]]s, better solutions can be achieved, and are often required to solve the largest and most complex problems.
* '''[[Conservation of momentum]]''' – The total momentum of objects involved in a collision remains constant regardless of friction and permanent deformation that may occur during the collision. The law of conservation of momentum can be used to analyse the interactions between objects, even in the presence of friction and other non-conservative forces. Conservation of momentum is a consequence of Newton's laws of motion.
* '''[[Constant speed drive]]''' – ('''CSD'''), is a type of [[transmission (mechanics)|transmission]] that takes an input shaft rotating at a wide range of speeds, delivering this power to an output shaft that rotates at a constant speed, despite the varying input. They are used to drive mechanisms, typically [[electrical generator]]s, that require a constant input speed.  The term is most commonly applied to [[hydrokinetic transmission|hydraulic transmissions]] found on the [[accessory drive]]s of [[gas turbine]] engines, such as aircraft [[jet engine]]s. On modern aircraft, the CSD is often combined with a generator into a single unit known as an '''integrated drive generator''' ('''IDG''').
* '''[[Control engineering]]''' – or '''control systems engineering''', is an [[engineering]] discipline that applies [[automatic control]] theory to design systems with desired behaviors in [[Control theory|control]] environments.<ref name="Case Western Reserve University">{{cite web|title=Systems & Control Engineering FAQ {{!}} Electrical Engineering and Computer Science|url=https://engineering.case.edu/eecs/node/213|website=engineering.case.edu|publisher=Case Western Reserve University|access-date=27 June 2017|language=en|date=20 November 2015}}</ref> The discipline of controls overlaps and is usually taught along with [[electrical engineering]] at many institutions around the world.<ref name="Case Western Reserve University" />
* '''Controllability''' – 
* '''[[Crew Exploration Vehicle]]''' – 
* '''[[Critical mach]]''' – In [[aerodynamics]], the '''critical Mach number (Mcr or M* )''' of an [[aircraft]] is the lowest [[Mach number]] at which the airflow over some point of the aircraft reaches the [[speed of sound]], but does not exceed it.<ref>Clancy, L.J. ''Aerodynamics'', Section 11.6</ref> At the '''lower critical Mach number''', airflow around the entire aircraft is subsonic.  At the '''upper critical Mach number''', airflow around the entire aircraft is supersonic.<ref name="RATHAKRISHNAN2013">{{cite book|author=E. Rathakrishnan|title=Gas Dynamics|url=https://books.google.com/books?id=uY31AAAAQBAJ&pg=PA278|date=3 September 2013|publisher=PHI Learning Pvt. Ltd.|isbn=978-81-203-4839-4|page=278}}</ref>
* '''[[Cylinder stress]]''' – In [[mechanics]], a '''cylinder stress''' is a [[stress (physics)|stress]] distribution with [[rotational symmetry]]; that is, which remains unchanged if the stressed object is rotated about some fixed axis.

== D ==

* '''[[Damage tolerance]]''' – is a property of a structure relating to its ability to sustain defects safely until repair can be effected. The approach to engineering design to account for damage tolerance is based on the assumption that flaws can exist in any structure and such flaws propagate with usage.
* '''[[Decalage]]''' – Decalage on a [[fixed-wing aircraft]] is the angle difference between the upper and lower wings of a [[biplane]], i.e. the acute angle contained between the [[Chord (aircraft)|chords]] of the wings in question.  Decalage is said to be positive when the upper wing has a higher [[angle of incidence (aerodynamics)|angle of incidence]] than the lower wing, and negative when the lower wing's incidence is greater than that of the upper wing. Positive decalage results in greater lift from the upper wing than the lower wing, the difference increasing with the amount of decalage.<ref>[http://aerade.cranfield.ac.uk/ara/1927/naca-tn-269.pdf NACA technical report No.269] {{webarchive|url=https://web.archive.org/web/20110716225431/http://aerade.cranfield.ac.uk/ara/1927/naca-tn-269.pdf |date=2011-07-16 }} ''The Distribution of Loads Between the Wings of a Biplane Having Decalage'' (November 1927), p.18. Retrieved on 9 February 2009.</ref>
* '''[[De Laval nozzle]]''' – (or '''convergent-divergent nozzle''', '''CD nozzle''' or '''con-di nozzle'''), is a tube that is pinched in the middle, making a carefully balanced, asymmetric [[hourglass]] shape. It is used to accelerate a hot, pressurized [[gas]] passing through it to a higher [[supersonic]] speed in the axial (thrust) direction, by converting the heat energy of the flow into [[kinetic energy]]. Because of this, the [[nozzle]] is widely used in some types of [[steam turbines]] and [[rocket engine nozzle]]s. It also sees use in supersonic [[jet engines]].
* '''[[Dead reckoning]]''' – In [[navigation]], dead reckoning is the process of calculating one's current position by using a previously determined position, or [[Fix (position)|fix]], and advancing that position based upon known or estimated speeds over elapsed time and course.
* '''[[Deflection (engineering)|Deflection]]''' – is the degree to which a structural element is displaced under a [[force|load]]. It may refer to an angle or a distance.
* '''[[Deformation (engineering)]]''' – In [[materials science]], deformation refers to any changes in the shape or size of an object due to an applied [[force (physics)|force]] (the deformation energy, in this case, is transferred through work) or a change in temperature (the deformation energy, in this case, is transferred through heat).
* '''[[Deformation (mechanics)]]''' – in [[continuum mechanics]] is the transformation of a body from a ''reference'' configuration to a ''current'' configuration.<ref name="Truesdell">{{cite book|last1=Truesdell |first1=C. |last2=Noll |first2=W. |year=2004 |title=The non-linear field theories of mechanics |url=https://archive.org/details/nonlinearfieldth00true_338 |url-access=limited |edition=3rd |publisher=Springer |page=[https://archive.org/details/nonlinearfieldth00true_338/page/n47 48]}}</ref> A configuration is a set containing the positions of all particles of the body.  A deformation may be caused by [[structural load|external loads]],<ref name="wu">{{cite book|first=H.-C. |last=Wu |title=Continuum Mechanics and Plasticity |publisher=CRC Press |date=2005 |isbn=1-58488-363-4}}</ref> [[body force]]s (such as [[gravity]] or [[electromagnetic force]]s), or changes in temperature, moisture content, or chemical reactions, etc.
* '''[[Delta-v]]''' – (literally "[[Delta (letter)#Upper case|change]] in [[velocity]]"), symbolised as '''∆''v''''' and pronounced ''delta-vee'', as used in [[flight dynamics (spacecraft)|spacecraft flight dynamics]], is a measure of the [[impulse (physics)|impulse]] that is needed to perform a maneuver such as launch from, or landing on a planet or moon, or in-space [[orbital maneuver]]. It is a [[scalar (mathematics)|scalar]] that has the units of [[speed]]. As used in this context, it is ''not'' the same as the [[delta-v (physics)|physical change in velocity]] of the vehicle.
* '''[[Delta-v budget]]''' – is an estimate of the total [[delta-v|delta-''v'']] required for a [[space mission]]. It is calculated as the sum of the delta-v required for the [[Spacecraft propulsion|propulsive]] [[orbital maneuver|maneuver]]s during the mission, and as input to the [[Tsiolkovsky rocket equation]], determines how much propellant is required for a vehicle of given mass and propulsion system.
* '''[[Delta wing]]''' – is a [[wing]] shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter [[delta (letter)|delta]] (Δ).  Although long studied, it did not find significant applications until the [[jet age]], when it proved suitable for high-speed subsonic and supersonic flight.
* '''[[Density]]''' – 
* '''[[Departure resistance]]''' – is a quality of an [[aircraft]] which enables it to remain in controlled flight and resist entering potentially dangerous less-controlled maneuvers such as [[spin (flight)|spin]].
* '''[[Derivative]]''' – The derivative of a [[function of a real variable]] measures the sensitivity to change of the function value (output value) with respect to a change in its argument (input value). Derivatives are a fundamental tool of [[calculus]].  For example, the derivative of the position of a moving object with respect to [[time]] is the object's [[velocity]]: this measures how quickly the position of the object changes when time advances.
* '''[[Digital Datcom]]''' – The [[United States]] [[United States Air Force|Air Force]] Stability and Control Digital DATCOM is a computer program that implements the methods contained in the [[USAF Stability and Control DATCOM]] to calculate the static stability, control and dynamic derivative characteristics of [[fixed-wing aircraft]].  Digital DATCOM requires an input file containing a geometric description of an aircraft, and outputs its corresponding dimensionless stability derivatives according to the specified flight conditions.  The values obtained can be used to calculate meaningful aspects of [[flight dynamics]].
* '''[[Dihedral (aeronautics)|Dihedral]]''' – Dihedral angle is the upward angle from horizontal of the wings or tailplane of a [[fixed-wing aircraft]].  "Anhedral angle" is the name given to negative dihedral angle, that is, when there is a ''downward'' angle from horizontal of the wings or tailplane of a fixed-wing aircraft.
* '''[[Disk loading]]''' – In [[fluid dynamics]], disk loading or disc loading is the average [[pressure]] change across an [[actuator disk]], such as an airscrew. Airscrews with a relatively low disk loading are typically called rotors, including [[helicopter]] [[Helicopter rotor|main rotor]]s and [[tail rotor]]s; [[propeller (aircraft)|propeller]]s typically have a higher disk loading.<ref name="isbn0-486-64647-5">{{cite book |author1=Keys, C. N. |author2=Stepniewski, W. Z. |title=Rotary-wing aerodynamics |publisher=Dover Publications |location=New York |year=1984 |pages=3 |isbn=0-486-64647-5 |quote=It is interesting to note that there has always been a strong intuitive association of rotary-wing aircraft with low disc loading which is reflected in the commonly accepted name of rotor given to their lifting airscrews.}}</ref> 
* '''[[Displacement (vector)]]''' – 
* '''[[Distance measuring equipment]]''' – (DME), is a radio navigation technology that measures the [[slant range]] (distance) between an aircraft and a ground station by timing the [[propagation delay]] of radio signals in the frequency band between 960 and 1215 megahertz (MHz).  Line-of-visibility between the aircraft and ground station is required.  An interrogator (airborne) initiates an exchange by transmitting a pulse pair, on an assigned ‘channel’, to the transponder ground station.  The channel assignment specifies the carrier frequency and the spacing between the pulses.  After a known delay, the transponder replies by transmitting a pulse pair on a frequency that is offset from the interrogation frequency by 63&nbsp;MHz and having specified separation.<ref name="ICAO">''Annex 10 to the Convention on International Civil Aviation, Volume I – Radio Navigation Aids''; International Civil Aviation Organization; International Standards and Recommended Practices.</ref>
* '''[[Distance measuring equipment|DME]]''' – distance measuring equipment.
* '''[[DO-178B]]''' – 
* '''[[DO-254]]''' – 
* '''[[Drag (physics)]]''' – In [[fluid dynamics]], drag (sometimes called air resistance, a type of [[friction]], or fluid resistance, another type of friction or fluid friction) is a [[force]] acting opposite to the relative motion of any object moving with respect to a surrounding fluid.<ref>{{cite web|url=http://www.merriam-webster.com/dictionary/drag|title=Definition of DRAG|website=www.merriam-webster.com|date=19 May 2023 }}</ref> This can exist between two fluid layers (or surfaces) or a fluid and a [[solid]] surface. Unlike other resistive forces, such as dry [[friction]], which are nearly independent of velocity, drag forces depend on velocity.<ref>French (1970), p. 211, Eq. 7-20</ref><ref name=NASAdrag>{{cite web|title=What is Drag?|url=http://www.grc.nasa.gov/WWW/k-12/airplane/drag1.html|access-date=2019-08-26|archive-url=https://web.archive.org/web/20100524003905/http://www.grc.nasa.gov/WWW/K-12/airplane/drag1.html|archive-date=2010-05-24|url-status=dead}}</ref>  Drag force is proportional to the velocity for a [[laminar flow]] and the squared velocity for a [[turbulent flow]]. Even though the ultimate cause of a drag is viscous friction, the turbulent drag is independent of [[viscosity]].<ref>{{cite book | author=G. Falkovich| year=2011 | title=Fluid Mechanics (A short course for physicists)|url=http://www.cambridge.org/gb/knowledge/isbn/item6173728/?site_locale=en_GB | publisher=Cambridge University Press | isbn=978-1-107-00575-4 }}</ref>  Drag forces always decrease fluid velocity relative to the solid object in the fluid's [[Pathline|path]].
* '''[[Drag coefficient]]''' – In [[fluid dynamics]], the drag coefficient (commonly denoted as: <math>\scriptstyle C_\mathrm d\,</math>, <math>\scriptstyle C_\mathrm x\,</math> or <math>\scriptstyle C_\mathrm w\,</math>) is a [[dimensionless quantity]] that is used to quantify the [[drag (physics)|drag]] or resistance of an object in a fluid environment, such as air or water. It is used in the [[drag equation]] in which a lower drag coefficient indicates the object will have less [[Aerodynamics|aerodynamic]] or [[Hydrodynamics|hydrodynamic]] drag. The drag coefficient is always associated with a particular surface area.<ref>McCormick, Barnes W. (1979): ''Aerodynamics, Aeronautics, and Flight Mechanics''. p. 24, John Wiley & Sons, Inc., New York, {{ISBN|0-471-03032-5}}</ref>
* '''[[Drag equation]]''' – In [[fluid dynamics]], the drag equation is a formula used to calculate the force of [[drag (physics)|drag]] experienced by an object due to movement through a fully enclosing [[fluid]]. The equation is:
::<math>F_D\, =\, \tfrac12\, \rho\, u^2\, C_D\, A</math>
:::<math>F_D</math> is the drag [[force]], which is by definition the force component in the direction of the flow velocity,
:::<math>\rho</math> is the [[mass density]] of the fluid,<ref>Note that for the [[Earth's atmosphere]], the air density can be found using the [[barometric formula]]. Air is 1.293 kg/m<sup>3</sup> at 0°C and 1  [[atmosphere (unit)|atmosphere]]</ref>
:::<math>u</math> is the [[flow velocity]] relative to the object,
:::<math>A</math> is the reference [[area]], and
:::<math>C_D</math> is the [[drag coefficient]] – a [[dimensionless number|dimensionless]] [[physical coefficient|coefficient]] related to the object's geometry and taking into account both [[skin friction]] and [[form drag]]. In general, <math>C_D</math> depends on the [[Reynolds number]].
* '''[[Drop test]]''' – is a method of testing the in-flight characteristics of [[prototype]] or [[experimental aircraft|experimental]] [[aircraft]] and [[spacecraft]] by raising the test vehicle to a specific altitude and then releasing it.  Test flights involving powered aircraft, particularly [[rocket-powered aircraft]], may be referred to as drop launches due to the [[Rocket launch|launch]] of the aircraft's rockets after release from its carrier aircraft.
* '''[[Dual mode propulsion rocket]]''' – Dual mode [[Spacecraft propulsion|propulsion]] systems combine the high efficiency of [[bipropellant rocket]]s with the reliability and simplicity of [[monopropellant rocket]]s. It is based upon the use of two [[rocket fuel]]s, [[liquid hydrogen]] and more dense hydrocarbon fuels, like RP, which are all burned with [[liquid oxygen]].<ref name="Napolitano2013">{{cite book|author=L. G. Napolitano|title=Applications of Space Developments: Selected Papers from the XXXI International Astronautical Congress, Tokyo, 21 – 28 September 1980|url=https://books.google.com/books?id=qdogBQAAQBAJ&pg=PA134|date=22 October 2013|publisher=Elsevier Science|isbn=978-1-4831-5976-8|pages=134–}}</ref>
* '''[[Ductility]]''' – is a measure of a material's ability to undergo significant plastic deformation before rupture, which may be expressed as percent elongation or percent area reduction from a tensile test.

== E ==

* '''[[Atmosphere of Earth|Earth's atmosphere]]''' – The atmosphere of Earth is the layer of [[gas]]es, commonly known as '''air''', that surrounds the planet [[Earth]] and is retained by [[gravity of Earth|Earth's gravity]]. The atmosphere of Earth protects [[life]] on Earth by creating [[atmospheric pressure|pressure]] allowing for [[liquid water]] to exist on the Earth's [[planetary surface|surface]], absorbing [[ultraviolet]] [[solar radiation]], warming the surface through heat retention ([[greenhouse effect]]), and reducing temperature extremes between [[daytime|day]] and [[night]] (the [[diurnal temperature variation]]).
* '''[[Eccentric anomaly]]''' – In [[orbital mechanics]], the eccentric anomaly is an [[keplerian element|angular parameter]] that defines the position of a body that is moving along an [[ellipse|elliptic]] [[Kepler orbit]]. The eccentric anomaly is one of three angular parameters ("anomalies") that define a position along an orbit, the other two being the [[true anomaly]] and the [[mean anomaly]].
* '''[[Eccentricity vector]]''' – In [[celestial mechanics]], the eccentricity vector of a [[Kepler orbit]] is the [[dimensionless]] [[vector (geometric)|vector]] with direction pointing from [[apoapsis]] to [[periapsis]] and with magnitude equal to the orbit's scalar [[orbital eccentricity|eccentricity]]. For Kepler orbits the eccentricity vector is a constant of motion. Its main use is in the analysis of almost circular orbits, as perturbing (non-Keplerian) forces on an actual orbit will cause the [[Osculating orbit|osculating]] eccentricity vector to change continuously. For the eccentricity and [[argument of periapsis]] parameters, eccentricity zero (circular orbit) corresponds to a singularity. The magnitude of the eccentricity vector represents the eccentricity of the orbit. Note that the velocity and position vectors need to be relative to the inertial frame of the central body.
* '''[[Eigenvector slew]]''' – In aerospace engineering, especially those areas dealing with [[spacecraft]], the eigenvector slew is a method to calculate a steering correction (called a '''[[Slew (spacecraft)|slew]]''') by rotating the spacecraft around '''one''' fixed axis, or a [[gimbal]].  This corresponds in general to the fastest and most efficient way to reach the desired target orientation as there is only one acceleration phase and one braking phase for the angular rate. If this fixed axis is not a [[Principal axis (mechanics)|principal axis]] a time varying torque must be applied to force the spacecraft to rotate as desired, though. Also the [[Gyroscope|gyroscopic]] effect of [[momentum wheels]] must be compensated for.
* '''[[Electrostatic ion thruster]]''' – is a form of [[electrically powered spacecraft propulsion|electric propulsion]] used for [[spacecraft propulsion]]. It creates [[thrust]] by accelerating [[ion]]s using [[electricity]].
* '''[[Elevator (aeronautics)|Elevator]]''' – is a [[flight control surfaces|flight control surface]], usually at the rear of an [[aircraft]], which control the aircraft's [[flight dynamics|pitch]], and therefore the [[angle of attack]] and the lift of the wing. The elevators are usually hinged to the [[tailplane]] or horizontal [[stabilizer (aircraft)|stabilizer]].
* '''[[Elliptic partial differential equation]]''' – 
* '''[[Empennage]]''' – The empennage ({{IPAc-en|ˌ|ɑː|m|p|ᵻ|ˈ|n|ɑː|ʒ}} or {{IPAc-en|ˈ|ɛ|m|p|ᵻ|n|ɪ|dʒ}}), also known as the '''tail''' or '''tail assembly''', is a structure at the rear of an aircraft that provides stability during flight, in a way similar to the feathers on an [[arrow]].<ref name="Cran2">Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', p. 194. Aviation Supplies & Academics, 1997. {{ISBN|1-56027-287-2}}</ref><ref name="GroundUp">Aviation Publishers Co. Limited, ''From the Ground Up'', p. 10 (27th revised edition) {{ISBN|0-9690054-9-0}}</ref><ref name="airlines">{{cite web|url = http://www.airlines.org/ATAResources/Handbook/Pages/AirlineHandbookChapter5HowAircraftFly.aspx |title=ATA Airline Handbook Chapter 5: How Aircraft Fly|access-date = 5 March 2013|last = Air Transport Association|author-link = Air Transport Association|date = 10 November 2011|archive-url=https://web.archive.org/web/20111110141033/http://www.airlines.org/ATAResources/Handbook/Pages/AirlineHandbookChapter5HowAircraftFly.aspx|archive-date=10 November 2011}}</ref> The term derives from the [[French language]] verb ''empenner'' which means "[[Fletching|to feather]] an arrow".<ref name="OxfordEtymology">{{cite web|title=Empennage|url=http://oxforddictionaries.com/definition/english/empennage|archive-url=https://web.archive.org/web/20120722152506/http://oxforddictionaries.com/definition/english/empennage|url-status=dead|archive-date=July 22, 2012|publisher=Oxford Dictionaries|work=Oxford Dictionaries Online|access-date=5 March 2013}}</ref> Most aircraft feature an empennage incorporating vertical and horizontal stabilising surfaces which stabilise the [[flight dynamics]] of [[Yaw (rotation)|yaw]] and [[pitch (flight)|pitch]],<ref name="Cran2" /><ref name="GroundUp" /> as well as housing [[flight control surface|control surface]]s.
* '''[[Enstrophy]]''' – In [[fluid dynamics]], the enstrophy {{mathcal|E}} can be interpreted as another type of [[potential density]]; or, more concretely, the quantity directly related to the [[kinetic energy]] in the flow model that corresponds to [[dissipation]] effects in the fluid. It is particularly useful in the study of [[turbulence|turbulent flows]], and is often identified in the study of [[Electrostatic ion thruster|thruster]]s as well as the field of [[combustion]] theory.

::Given a domain <math>\Omega \subseteq \R^n</math> and a once-weakly differentiable vector field <math>u \in H^1(\R^n)^n</math> which represents a fluid flow, such as a solution to the [[Navier–Stokes equations|Navier-Stokes equations]], its enstrophy is given by:<ref>{{Cite book|url=https://www.worldcat.org/oclc/56416088|title=Navier-Stokes equations and turbulence|date=2001|publisher=Cambridge University Press|first=Ciprian |last=Foiaş|isbn=0-511-03936-0|location=Cambridge|pages=28–29|oclc=56416088}}</ref>

::<math>\mathcal{E}(u) := \int_\Omega |\nabla \mathbf{u}|^2 \, dx</math>

::Where <math> |\nabla \mathbf{u}|^2 = \sum_{i,j=1}^n \left| \partial_i u^j \right|^2 </math>. This is quantity is the same as the squared [[seminorm]] <math>|\mathbf{u}|_{H^1(\Omega)^n}^2</math>of the solution in the [[Sobolev space]] ::::<math>H^1(\Omega)^n</math>.

::In the case that the flow is [[Incompressible flow|incompressible]], or equivalently that <math> \nabla \cdot \mathbf{u} = 0 </math>, the enstrophy can be described as the integral of the square of the [[vorticity]] <math> \mathbf{\omega} </math>,<ref>Doering, C. R. and Gibbon, J. D. (1995). ''Applied Analysis of the Navier-Stokes Equations'', p. 11, Cambridge University Press, Cambridge. {{ISBN|052144568-X}}.</ref>

::<math> \mathcal{E}(\boldsymbol \omega) \equiv \int_\Omega |\boldsymbol \omega|^2 \,dx </math>

::or, in terms of the [[flow velocity]],

::<math> \mathcal{E}(\mathbf{u}) \equiv \int_{S} |\nabla \times \mathbf u|^2 \,dS \,. </math>

::In the context of the incompressible Navier-Stokes equations, enstrophy appears in the following useful result<ref name=":0" />

::<math> \frac{d}{dt} \left( \frac{1}{2} \int_\Omega |\mathbf{u}|^2 \right) = - \nu \mathcal{E}(\mathbf{u}) </math>

::The quantity in parentheses on the left is the energy in the flow, so the result says that energy declines proportional to the [[Viscosity|kinematic viscosity]] <math> \nu </math> times the enstrophy.

* '''[[Equations of motion]]''' – In [[physics]], equations of motion are [[equation]]s that describe the behavior of a [[physical system]] in terms of its [[Motion (physics)|motion]] as a [[function (mathematics)|function]] of time.<ref name="Physics 1991">''Encyclopaedia of Physics'' (second Edition), [[Rita G. Lerner|R.G. Lerner]], G.L. Trigg, VHC Publishers, 1991, ISBN (Verlagsgesellschaft) 3-527-26954-1 (VHC Inc.) 0-89573-752-3</ref> More specifically, the equations of motion describe the behavior of a physical system as a set of mathematical functions in terms of dynamic variables. These variables are usually spatial coordinates and time, but may include [[momentum]] components. The most general choice are [[generalized coordinates]] which can be any convenient variables characteristic of the physical system.<ref name="Analytical Mechanics 2008">''Analytical Mechanics'', L.N. Hand, J.D. Finch, Cambridge University Press, 2008, {{ISBN|978-0-521-57572-0}}</ref> The functions are defined in a [[Euclidean space]] in [[classical mechanics]], but are replaced by [[curved space]]s in [[Theory of relativity|relativity]]. If the [[Dynamics (mechanics)|dynamics]] of a system is known, the equations are the solutions for the [[differential equations]] describing the motion of the dynamics.
* '''[[ESA]]''' – European Space Agency
* '''ET''' – [[Space Shuttle external tank|(Space Shuttle) external tank]]
* '''[[Euler angles]]''' – are three angles introduced by [[Leonhard Euler]] to describe the [[Orientation (geometry)|orientation]] of a [[rigid body]] with respect to a fixed [[coordinate system]].<ref name="Euler">Novi Commentarii academiae scientiarum Petropolitanae 20, 1776, pp. 189–207 (E478) [https://math.dartmouth.edu/~euler/docs/originals/E478.pdf PDF]</ref>  They can also represent the orientation of a mobile [[frame of reference]] in physics or the orientation of a general [[Basis (linear algebra)|basis]] in [[dimension|3-dimensional]] linear algebra. Alternative forms were later introduced by [[Peter Guthrie Tait]] and [[George H. Bryan]] intended for use in aeronautics and engineering.
* '''[[European Space Agency]]''' – 
* '''[[Expander cycle (rocket)]]''' – is a power cycle of a [[bipropellant rocket]] [[engine]]. In this cycle, the fuel is used to cool the engine's combustion chamber, picking up heat and changing phase. The now heated and gaseous fuel then powers the turbine that drives the engine's fuel and oxidizer pumps before being injected into the combustion chamber and burned for thrust.

== F ==

* '''[[Fatigue (material)|Fatigue]]''' – In [[materials science]], fatigue is the weakening of a material caused by repeatedly applied loads. It is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum [[stress (physics)|stress]] values that cause such damage may be much less than the strength of the material typically quoted as the [[tensile strength|ultimate tensile stress limit]], or the [[tensile strength|yield stress limit]].
* '''[[Field-emission electric propulsion]]''' – (FEEP), is an advanced electrostatic space propulsion concept, a form of [[ion thruster]], that uses a liquid [[metal]] as a propellant – usually either [[caesium]], [[indium]], or [[mercury (element)|mercury]].
* '''[[Fixed-wing aircraft]]''' – is a heavier-than-air [[Aircraft|flying machine]], such as an [[airplane]], which is capable of [[flight]] using [[wing]]s that generate [[Lift (force)|lift]] caused by the aircraft's forward [[airspeed]] and the [[wing configuration|shape of the wings]]. Fixed-wing aircraft are distinct from [[rotorcraft|rotary-wing aircraft]] (in which the wings form a [[Helicopter rotor|rotor]] mounted on a spinning shaft or "mast"), and [[ornithopter]]s (in which the wings [[bird flight#Flapping flight|flap]] in a manner similar to that of a [[bird]]). The wings of a fixed-wing aircraft are not necessarily rigid; kites, [[hang glider]]s, [[variable-sweep wing]] aircraft and airplanes that use [[wing morphing]] are all examples of fixed-wing aircraft.
* '''Flange''' – 
* '''[[Flap (aeronautics)|Flap]]''' – is a [[high-lift device]] used to reduce the [[stall (flight)|stalling speed]] of an [[aircraft]] [[wing]] at a given weight. Flaps are usually mounted on the wing trailing edges of a [[fixed-wing aircraft]]. Flaps are used to reduce the take-off distance and the landing distance. Flaps also cause an increase in [[Drag (physics)|drag]] so they are retracted when not needed.
* '''[[Flight control surfaces]]''' – are aerodynamic devices allowing a pilot to adjust and control the aircraft's flight [[Aircraft attitude|attitude]].
* '''[[Aircraft flight control system|Flight control system (aircraft)]]''' – A conventional [[Fixed-wing aircraft|fixed-wing]] '''aircraft flight control system''' consists of [[flight control surfaces]], the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight. [[Aircraft engine controls]] are also considered as flight controls as they change speed.
* '''[[Helicopter flight controls|Flight control system (helicopter)]]''' – A [[helicopter]] [[aviator|pilot]] manipulates the '''helicopter flight controls''' to achieve and maintain controlled aerodynamic [[flight]].<ref>Gablehouse, Charles (1969) ''Helicopters and Autogiros: a History of Rotating-Wing and V/STOL Aviation.'' Lippincott. p.206</ref> Changes to the [[aircraft flight control system]] transmit mechanically to the rotor, producing aerodynamic effects on the rotor blades that make the helicopter move in a deliberate way. To tilt forward and back (pitch) or sideways (roll) requires that the controls alter the [[angle of attack]] of the main rotor blades ''cyclically'' during rotation, creating differing amounts of [[lift (force)]] at different points in the cycle. To increase or decrease overall lift requires that the controls alter the [[angle of attack]] for all blades ''collectively'' by equal amounts at the same time, resulting in ascent, descent, acceleration and deceleration.
* '''[[Flight dynamics]]''' – is the study of the performance, stability, and control of vehicles [[flight|flying]] through the air or in [[outer space]].<ref>{{Citation | last = Stengel | first = Robert F. | title = Aircraft Flight Dynamics (MAE 331) course summary | year = 2010 | url = http://www.princeton.edu/~stengel/MAE331.html | access-date = November 16, 2011 }}
</ref> It is concerned with how forces acting on the vehicle determine its [[velocity]] and [[Spacecraft attitude control|attitude]] with respect to time.  For a [[fixed-wing aircraft]], its changing [[Orientation (geometry)|orientation]] with respect to the local air flow is represented by two critical angles, the angle of attack of the wing ("alpha") and the angle of attack of the vertical tail, known as the [[slip (aerodynamics)|sideslip]] angle ("beta"). A sideslip angle will arise if an aircraft yaws about its centre of gravity and if the aircraft sideslips bodily, i.e. the centre of gravity moves sideways.<ref>Flightwise - Volume 2 - Aircraft Stability And Control, Chris Carpenter 1997, Airlife Publishing Ltd., {{ISBN|1 85310 870 7}}, p.145</ref> These angles are important because they are the principal source of changes in the aerodynamic forces and moments applied to the aircraft.  Spacecraft flight dynamics involve three main forces: propulsive (rocket engine), gravitational, and atmospheric resistance.<ref name="auto">Depending on the vehicle's mass distribution, the effects of gravitational force may also be affected by attitude (and vice versa), but to a much lesser extent.</ref> Propulsive force and atmospheric resistance have significantly less influence over a given spacecraft compared to gravitational forces.
* '''[[Flight management system]]''' – A flight management system (FMS) is a fundamental component of a modern airliner's [[avionics]]. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern civilian aircraft no longer carry [[flight engineer]]s or [[navigator]]s. A primary function is in-flight management of the flight plan. Using various sensors (such as [[GPS]] and [[Inertial navigation system|INS]] often backed up by [[radio navigation]]) to determine the aircraft's position, the FMS can guide the aircraft along the flight plan. From the cockpit, the FMS is normally controlled through a [[Control Display Unit]] (CDU) which incorporates a small screen and keyboard or touchscreen. The FMS sends the flight plan for display to the [[Electronic Flight Instrument System]] (EFIS), Navigation Display (ND), or Multifunction Display (MFD). The FMS can be summarised as being a dual system consisting of the '''Flight Management Computer (FMC)''', CDU and a cross talk bus.
* '''[[Floatstick]]''' – is a device to measure [[fuel]] levels in modern large [[aircraft]]. It consists of a closed tube rising from the bottom of the fuel tank.  Surrounding the tube is a ring-shaped float, and inside it is a graduated rod indicating fuel capacity.  The float and the top of the rod contain [[magnet]]s.  The rod is withdrawn from the bottom of the [[wing]] until the magnets stick, the distance it is withdrawn indicating the level of the fuel.  When not in use, the stick is secured within the tube.
* '''[[Fluid]]''' – In [[physics]], a fluid is a [[liquid]], [[gas]], or other material that continuously [[Deformation (physics)|deforms]] (flows) under an applied [[shear stress]], or external force.<ref>{{cite web |title=Fluid {{!}} Definition, Models, Newtonian Fluids, Non-Newtonian Fluids, & Facts |url=https://www.britannica.com/science/fluid-physics |website=Encyclopedia Britannica |access-date=2 June 2021 |language=en}}</ref> They have zero [[shear modulus]], or, in simpler terms, are [[Matter|substances]] which cannot resist any [[shear force]] applied to them. 
* '''[[Fluid dynamics]]''' – In [[physics]] and [[engineering]], fluid dynamics  is a subdiscipline of [[fluid mechanics]] that describes the flow of [[fluid]]s—[[liquid]]s and [[gas]]es.  It has several subdisciplines, including [[aerodynamics]] (the study of air and other gases in motion) and '''hydrodynamics''' (the study of liquids in motion).  Fluid dynamics has a wide range of applications, including calculating [[force]]s and [[moment (physics)|moment]]s on [[aircraft]], determining the [[mass flow rate]] of [[petroleum]] through [[pipeline transport|pipelines]], [[weather forecasting|predicting weather pattern]]s, and understanding [[nebula]]e in [[interstellar space]].
* '''[[Fluid mechanics]]''' – is the branch of [[physics]] concerned with the [[mechanics]] of [[fluid]]s ([[liquid]]s, [[gas]]es, and [[plasma (physics)|plasma]]s) and the [[force]]s on them.<ref name="White, Frank M. 2011">White, Frank M. (2011). Fluid Mechanics (7th ed.). McGraw-Hill. ISBN 978-0-07-352934-9.</ref>  It has applications in a wide range of disciplines, including [[mechanical engineering|mechanical]], [[civil engineering|civil]], [[chemical engineering|chemical]] and [[biomedical engineering]], [[geophysics]], [[oceanography]], [[meteorology]], [[astrophysics]], and [[biology]].  It can be divided into [[fluid statics]], the study of fluids at rest; and [[fluid dynamics]], the study of the effect of forces on fluid motion.<ref name="White, Frank M. 2011"/>
* '''[[Fluid statics]]''' – or '''hydrostatics''', is the branch of [[fluid mechanics]] that studies the condition of the equilibrium of a floating body and submerged body "[[fluid]]s at [[hydrostatic equilibrium]]<ref name="en.wikibooks.org">{{Cite web|title=Fluid Mechanics/Fluid Statics/mentals of Fluid Statics - Wikibooks, open books for an open world|url=https://en.wikibooks.org/wiki/Fluid_Mechanics/Fluid_Statics/Fundamentals_of_Fluid_Statics#Hydrostatic_Equilibrium|access-date=2021-04-01|website=en.wikibooks.org|language=en}}</ref> and the pressure in a fluid, or exerted by a fluid, on an immersed body".<ref name="MW dictionary def">{{cite web |title=Hydrostatics |url=https://www.merriam-webster.com/dictionary/hydrostatics |website=Merriam-Webster |access-date=11 September 2018}}</ref>
* '''[[Flight management system|FMS]]''' – Flight management system.
* '''[[Force]]''' – In [[physics]], a force is any influence that, when unopposed, will change the [[motion (physics)|motion]] of an [[Physical object|object]]. A force can cause an object with [[mass]] to change its [[velocity]] (which includes to begin moving from a [[Newton's first law|state of rest]]), i.e., to [[accelerate]]. Force can also be described intuitively as a push or a pull. A force has both [[Euclidean vector#Length|magnitude]] and [[Direction (geometry, geography)|direction]], making it a [[Vector (geometric)|vector]] quantity.  It is measured in the [[SI unit]] of [[newton (unit)|newton (N)]]. Force is represented by the symbol {{math|'''F'''}} (formerly {{math|'''P'''}}).
* '''[[Freefall]]''' – In [[Classical mechanics|Newtonian physics]], free fall is any motion of a [[physical body|body]] where [[gravity]] is the only [[force]] acting upon it.  In the context of [[general relativity]], where gravitation is reduced to a [[space-time curvature]], a body in free fall has no force acting on it.  An object in the technical sense of the term "free fall" may not necessarily be falling down in the usual sense of the term. An object moving upwards might not normally be considered to be falling, but if it is subject to only the force of gravity, it is said to be in free fall.  The [[Moon]] is thus in free fall around the [[Earth]], though its [[orbital speed]] keeps it in [[orbit of the Moon|very far orbit]] from the [[Earth's surface]].  In a roughly uniform [[gravitational field]], in the absence of any other forces, gravitation acts on each part of the body roughly equally.  When there is no [[normal force]] exerted between a body (e.g. an [[astronaut]] in orbit) and its surrounding objects, it will result in the sensation of [[weightlessness]], a condition that also occurs when the gravitational field is weak (such as when far away from any source of gravity).
* '''[[Fuselage]]''' – In [[aeronautics]], the fuselage ({{IPAc-en|ˈ|f|juː|z|əl|ɑː|ʒ}}; from the [[French language|French]] ''fuselé'' "spindle-shaped") is an [[aircraft]]'s main body section. It holds [[Aircrew|crew]], passengers, or [[cargo]]. In single-engine aircraft, it will usually contain an [[Aircraft engine|engine]], as well, although in some [[amphibious aircraft]] the single engine is mounted on a [[hardpoint|pylon]] attached to the fuselage, which in turn is used as a floating [[Hull (watercraft)|hull]]. The fuselage also serves to position the [[Flight control surfaces|control]] and [[Stabilizer (aeronautics)|stabilization surfaces]] in specific relationships to [[Surface lift|lifting surfaces]], which is required for aircraft stability and maneuverability.
* '''[[Future Air Navigation System]]''' – (FANS), is an [[avionics]] system which provides direct data link communication between the pilot and the [[air traffic controller]]. The communications include air traffic control clearances, pilot requests and position reporting.<ref>{{Cite web |url=http://icrat.org/seminarContent/seminar4/papers/p_181_S.pdf |title=An Assessment of Flight Crew Experiences with FANS-1 ATC Data Link |access-date=2021-09-23 |archive-date=2021-10-17 |archive-url=https://web.archive.org/web/20211017194828/http://icrat.org/seminarContent/seminar4/papers/p_181_S.pdf |url-status=dead }}</ref>
* '''[[Flying wing]]''' – is a [[tailless aircraft|tailless]] [[fixed-wing aircraft]] that has no definite [[fuselage]], with its crew, payload, fuel, and equipment housed inside the main wing structure. A flying wing may have various small protuberances such as pods, [[nacelle]]s, blisters, booms, or [[vertical stabilizer]]s.<ref name="Crane">Crane, Dale: ''Dictionary of Aeronautical Terms'', third edition, p. 224. Aviation Supplies & Academics, 1997. {{ISBN|1-56027-287-2}}.</ref>

== G ==

* '''[[Galaxy]]''' – is a [[gravitation]]ally bound system of [[star]]s, [[stellar remnant]]s, [[interstellar medium|interstellar gas]], [[cosmic dust|dust]], and [[dark matter]].<ref>Sparke, L. S.; Gallagher, J. S. III (2000). Galaxies in the Universe: An Introduction. Cambridge University Press. ISBN 978-0-521-59740-1. Archived from the original on March 24, 2021. Retrieved July 25, 2018.</ref><ref>Hupp, E.; Roy, S.; Watzke, M. (August 12, 2006). "NASA Finds Direct Proof of Dark Matter". NASA. Archived from the original on March 28, 2020. Retrieved April 17, 2007.</ref> The word is derived from the [[Ancient Greek|Greek]] ''{{transliteration|grc|galaxias}}'' ({{lang|grc|γαλαξίας}}), literally "milky", a reference to the [[Milky Way]]. Galaxies range in size from [[dwarf galaxy|dwarfs]] with just a few hundred million ({{10^|8}}) stars to [[IC 1101|giants]] with one hundred [[Orders of magnitude (numbers)#1012|trillion]] ({{10^|14}}) stars,<ref>Uson, J. M.; Boughn, S. P.; Kuhn, J. R. (1990). "The central galaxy in Abell 2029 – An old supergiant". Science. 250 (4980): 539–540. Bibcode:1990Sci...250..539U. doi:10.1126/science.250.4980.539. PMID 17751483. S2CID 23362384.</ref> each orbiting its galaxy's [[center of mass]].  Galaxies are categorized according to their visual [[morphology (astronomy)|morphology]] as [[elliptical galaxy|elliptical]],<ref>Hoover, A. (June 16, 2003). "UF Astronomers: Universe Slightly Simpler Than Expected". Hubble News Desk. Archived from the original on July 20, 2011. Retrieved March 4, 2011.
Based upon: Graham, A. W.; Guzman, R. (2003). "HST Photometry of Dwarf Elliptical Galaxies in Coma, and an Explanation for the Alleged Structural Dichotomy between Dwarf and Bright Elliptical Galaxies". The Astronomical Journal. 125 (6): 2936–2950. arXiv:astro-ph/0303391. Bibcode:2003AJ....125.2936G. doi:10.1086/374992. S2CID 13284968.</ref> [[Spiral galaxy|spiral]], or [[irregular galaxy|irregular]].<ref>Jarrett, T. H. "Near-Infrared Galaxy Morphology Atlas". California Institute of Technology. Archived from the original on August 2, 2012. Retrieved January 9, 2007.</ref> 
* '''[[Gas-generator cycle (rocket)]]''' – is a power cycle of a pumped liquid [[bipropellant rocket]] [[rocket engine|engine]]. Part of the unburned propellant is burned in a [[gas generator]] (or preburner) and the resulting hot gas is used to power the propellant pumps before being exhausted overboard, and lost. Because of this loss, this type of engine is termed '''open cycle'''.
* '''[[Geostationary orbit]]''' – also referred to as a '''geosynchronous equatorial orbit'''<ref group=lower-alpha>''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources.</ref> ('''GEO'''), is a [[circular orbit|circular]] [[geosynchronous orbit]] {{convert|35786|km|mi|abbr=off}} in altitude above Earth's [[equator]] (42,164 kilometers in radius from Earth's center) and following the [[retrograde and prograde motion|direction]] of [[Earth's rotation]].  An object in such an orbit has an [[orbital period]] equal to the Earth's rotational period, one [[sidereal day]], and so to ground observers it appears motionless, in a fixed position in the sky.
* '''[[Geosynchronous orbit]]''' –  (sometimes abbreviated GSO) is an Earth-centered [[orbit]] with an [[orbital period]] that matches [[Earth's rotation]] on its axis, 23 hours, 56 minutes, and 4 seconds (one [[sidereal day]]). The synchronization of rotation and orbital period means that, for an observer on Earth's surface, an object in geosynchronous orbit returns to exactly the same position in the sky after a period of one sidereal day. Over the course of a day, the object's position in the sky may remain still or trace out a path, [[Analemma#Of geosynchronous satellites|typically in a figure-8 form]], whose precise characteristics depend on the orbit's [[orbital inclination|inclination]] and [[orbital eccentricity|eccentricity]]. A circular geosynchronous orbit has a constant altitude of {{convert|35786|km|mi|0|abbr=on}}, and all geosynchronous orbits share that semi-major axis.  A special case of geosynchronous orbit is the [[geostationary orbit]], which is a circular geosynchronous orbit in Earth's [[celestial equator|equatorial plane]]. A satellite in a geostationary orbit remains in the same position in the sky to observers on the surface.
* '''[[Glide ratio]]''' – As the aircraft [[fuselage]] and control surfaces will also add drag and possibly some lift, it is fair to consider the lift-to-drag ratio (or L/D ratio) of the aircraft as a whole. As it turns out, the [[Gliding (flight)#Glide ratio|glide ratio]], which is the ratio of an (unpowered) aircraft's forward motion to its descent, is (when flown at constant speed) numerically equal to the aircraft's L/D. This is especially of interest in the design and operation of high performance [[sailplane]]s, which can have glide ratios almost 60 to 1 (60 units of distance forward for each unit of descent) in the best cases, but with 30:1 being considered good performance for general recreational use. Achieving a glider's best L/D in practice requires precise control of airspeed and smooth and restrained operation of the controls to reduce drag from deflected control surfaces. In zero wind conditions, L/D will equal distance traveled divided by altitude lost. Achieving the maximum distance for altitude lost in wind conditions requires further modification of the best airspeed, as does alternating cruising and thermaling.  To achieve high speed across country, glider pilots anticipating strong thermals often load their gliders (sailplanes) with [[Gliding competitions#Water ballast|water ballast]]: the increased [[wing loading]] means optimum glide ratio at greater airspeed, but at the cost of climbing more slowly in thermals.  The maximum L/D is not dependent on weight or wing loading, but with greater wing loading the maximum L/D occurs at a faster airspeed.  Also, the faster airspeed means the aircraft will fly at greater [[Reynolds number]] and this will usually bring about a lower [[zero-lift drag coefficient]].
* '''[[Glider (aircraft)|Glider]]''' – is a [[fixed-wing aircraft]] that is supported in flight by the dynamic reaction of the air against its lifting surfaces, and whose [[gliding flight|free flight]] does not depend on an engine.<ref>[http://www.faa.gov/library/manuals/aircraft/glider_handbook/media/faa-h-8083-13.pdf FAA Glider handbook] {{webarchive|url=https://web.archive.org/web/20090206073836/http://www.faa.gov/library/manuals/aircraft/glider_handbook/media/faa-h-8083-13.pdf |date=2009-02-06 }}</ref> Most gliders do not have an engine, although [[motor-glider]]s have small engines for extending their flight when necessary by sustaining the altitude (normally a sailplane relies on rising air to maintain altitude) with some being powerful enough to take off [[Motor glider|self-launch]].
* '''[[Global Positioning System]]''' – (GPS), originally '''Navstar GPS''',<ref>(1) "GPS: Global Positioning System (or Navstar Global Positioning System)" Wide Area Augmentation System (WAAS) Performance Standard, Section B.3, Abbreviations and Acronyms.<br />(2) {{cite web |url=http://www.gps.gov/technical/ps/2008-WAAS-performance-standard.pdf |title=GLOBAL POSITIONING SYSTEM WIDE AREA AUGMENTATION SYSTEM (WAAS) PERFORMANCE STANDARD|archiveurl=https://web.archive.org/web/20170427033332/http://www.gps.gov/technical/ps/2008-WAAS-performance-standard.pdf|archivedate=April 27, 2017|date=January 3, 2012}}</ref> is a [[Radionavigation-satellite service|satellite-based radionavigation]] system owned by the [[United States government]] and operated by the [[United States Space Force]].<ref>{{cite web |url=http://www.gps.gov/technical/ps/2008-SPS-performance-standard.pdf |title=Global Positioning System Standard Positioning Service Performance Standard : 4th Edition, September 2008 |access-date=April 21, 2017 |archive-url=https://web.archive.org/web/20170427025348/http://www.gps.gov/technical/ps/2008-SPS-performance-standard.pdf |archive-date=April 27, 2017 |url-status=live }}</ref> It is one of the [[satellite navigation|global navigation satellite systems]] (GNSS) that provides [[geolocation]] and [[Time transfer|time information]] to a [[Satellite navigation device|GPS receiver]] anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites.<ref>{{cite web|title=What is a GPS?|website=[[Library of Congress]]|url=https://www.loc.gov/rr/scitech/mysteries/global.html|access-date=January 28, 2018|archive-url=https://web.archive.org/web/20180131184150/http://www.loc.gov/rr/scitech/mysteries/global.html|archive-date=January 31, 2018|url-status=live}}</ref> Obstacles such as mountains and buildings can block the relatively weak [[GPS signals]].
* '''[[Goddard problem]]''' – In [[rocket]]ry, the Goddard problem is to optimize the peak [[altitude]] of a rocket, ascending vertically, and taking into account [[atmospheric drag]] and the [[gravitational field]]. This was first posed by [[Robert H. Goddard]] in his 1919 publication, "A Method of Reaching Extreme Altitudes".<ref>{{cite web |url=http://www.dept.aoe.vt.edu/~cliff/aoe5244_99/week_13_a.pdf |title=Goddard Problem (slides) |author= E.M. Cliff |access-date=2010-04-29 |url-status=live |archive-url=https://web.archive.org/web/20100624035050/http://www.aoe.vt.edu/~cliff/aoe5244_99/week_13_a.pdf |archive-date=2010-06-24}}</ref><ref>{{cite report |url= https://apps.dtic.mil/sti/citations/AD0409855 |archive-url= https://web.archive.org/web/20210927132400/https://apps.dtic.mil/sti/citations/AD0409855 |url-status= live |archive-date= September 27, 2021 |title=A Solution of the Goddard Problem |author= Boris Garfinkel}}</ref>
* '''[[GPS]]''' – Global Positioning System
* '''[[Gravitational constant]]''' – The gravitational constant (also known as the '''universal gravitational constant''', the '''Newtonian constant of gravitation''', or the '''Cavendish gravitational constant'''),{{efn|"Newtonian constant of gravitation" is the name introduced for ''G'' by Boys (1894). Use of the term by  T.E. Stern (1928) was misquoted as "Newton's constant of gravitation" in ''Pure Science Reviewed for Profound and Unsophisticated Students'' (1930), in what is apparently the first use of that term. Use of "Newton's constant" (without specifying "gravitation" or "gravity") is more recent, as "Newton's constant" was also
used for the [[heat transfer coefficient]] in [[Newton's law of cooling]], but has by now become quite common, e.g.
Calmet et al, ''Quantum Black Holes'' (2013), p. 93;  P. de Aquino, ''Beyond Standard Model Phenomenology at the LHC'' (2013), p. 3.  The name "Cavendish gravitational constant", sometimes "Newton–Cavendish gravitational constant", appears to have been common in the 1970s to 1980s, especially in (translations from) Soviet-era Russian literature, e.g. Sagitov (1970 [1969]), ''Soviet Physics: Uspekhi'' 30 (1987), Issues 1–6, p. 342 [etc.].
"Cavendish constant" and "Cavendish gravitational constant" is also used in Charles W. Misner, Kip S. Thorne, John Archibald Wheeler, "Gravitation",  (1973), 1126f.  Colloquial use of "Big G", as opposed to "[[little g]]" for gravitational acceleration dates to the 1960s (R.W.  Fairbridge, ''The encyclopedia of atmospheric sciences and astrogeology'', 1967, p. 436; note use of "Big G's" vs. "little g's" as early as the 1940s of the [[Einstein tensor]] ''G''<sub>''μν''</sub> vs. the [[metric tensor]] ''g''<sub>''μν''</sub>, ''Scientific, medical, and technical books published in the United States of America: a selected list of titles in print with annotations: supplement of books published 1945–1948'', Committee on American Scientific and Technical Bibliography National Research Council, 1950, p. 26).|name=|group=}} denoted by the letter {{math|''G''}}, is an [[empirical]] [[physical constant]] involved in the calculation of [[gravitational]] effects in [[Sir Isaac Newton]]'s [[Newton's law of universal gravitation|law of universal gravitation]] and in [[Albert Einstein]]'s [[general relativity|general theory of relativity]].  In Newton's law, it is the proportionality constant connecting the [[gravitational force]] between two bodies with the product of their [[mass]]es and the [[inverse-square law|inverse square]] of their [[distance]]. In the [[Einstein field equations]], it quantifies the relation between the geometry of spacetime and the energy&ndash;momentum tensor (also referred to as the [[stress–energy tensor]]).  The measured value of the constant is known with some certainty to four significant digits. In [[SI units]], its value is approximately <!--{{math|''G''}} = -->{{physconst|G|after=.|round=3}}  The modern notation of Newton's law involving {{math|''G''}} was introduced in the 1890s by [[C. V. Boys]]. The first implicit measurement with an accuracy within about 1% is attributed to [[Henry Cavendish]] in a [[Cavendish experiment|1798 experiment]].{{efn|Cavendish determined the value of ''G'' indirectly, by reporting a value for the [[Earth's mass]], or the average density of Earth, as {{val|5.448|u=g.cm-3}}.|name=|group=}}
* '''[[Gravitational slingshot]]''' – In [[orbital mechanics]] and [[aerospace engineering]], a gravitational [[slingshot]], '''gravity assist maneuver''', or '''swing-by''' is the use of the relative movement (e.g. orbit around the [[Sun]]) and [[gravity]] of a [[planet]] or other [[astronomical object]] to alter the [[Course (navigation)|path]] and [[speed]] of a [[spacecraft]], typically to save [[propellant]] and reduce expense.  Gravity assistance can be used to [[accelerate]] a spacecraft, that is, to increase or decrease its speed or redirect its path. The "assist" is provided by the motion of the gravitating body as it pulls on the spacecraft.<ref name="basics-traject">{{cite web |url=https://solarsystem.nasa.gov/basics/chapter4-1 |title=Section 1: Environment, Chapter 4: Trajectories |series=Basics of Space Flight |publisher=NASA |access-date=21 July 2018}}</ref> 
* '''[[Gravity]]''' – ({{Etymology|lat|gravitas|weight}}<ref>{{Cite web |url=https://browse.dict.cc/latin-english/gravitas.html |title=dict.cc dictionary :: gravitas :: English-Latin translation |access-date=11 September 2018 |archive-date=13 August 2021 |archive-url=https://web.archive.org/web/20210813203625/https://browse.dict.cc/latin-english/gravitas.html |url-status=live }}</ref>), or '''gravitation''', is a [[list of natural phenomena|natural phenomenon]] by which all things with [[mass]] or [[energy]]—including [[planet]]s, [[star]]s, [[galaxy|galaxies]], and even [[electromagnetic radiation|light]]<ref name="Comins">{{cite book
 | last1  = Comins
 | first1  = Neil F.
 | last2  = Kaufmann
 | first2  = William J.
 | title  = Discovering the Universe: From the Stars to the Planets
 | publisher  = MacMillan
 | date  = 2008
 | pages  = 347
 | url  = https://books.google.com/books?id=J1d9HJHlISkC&pg=PA347
 | isbn  = 978-1429230421
 | bibcode  = 2009dufs.book.....C
 | access-date  = 8 May 2018
 | archive-date  = 25 January 2020
 | archive-url  = https://web.archive.org/web/20200125200736/https://books.google.com/books?id=J1d9HJHlISkC&pg=PA347
 | url-status  = live
 }}</ref>—are attracted to (or ''gravitate'' toward) one another.  [[Gravity of Earth|On Earth]], gravity gives [[weight]] to [[physical object]]s, and the [[gravitation of the Moon|Moon's gravity]] causes the [[tide]]s of the oceans. The gravitational attraction of the original gaseous matter present in the [[Universe]] caused it to begin [[coalescence (physics)|coalescing]] and [[star formation|forming stars]] and caused the stars to group together into galaxies, so gravity is responsible for many of the large-scale structures in the Universe. Gravity has an infinite range, although its effects become weaker as objects get further away.

== H ==

* '''[[Hall effect thruster]]''' – In [[spacecraft propulsion]], a Hall-effect thruster (HET) is a type of [[ion thruster]] in which the [[propellant]] is accelerated by an [[electric field]]. Hall-effect thrusters (based on the discovery by [[Edwin Hall]]) are sometimes referred to as '''Hall thrusters''' or '''Hall-current thrusters'''. [[Hall effect|Hall-effect]] thrusters use a [[magnetic field]] to limit the electrons' axial motion and then use them to ionize propellant, efficiently accelerate the [[ion]]s to produce [[thrust]], and neutralize the ions in the plume. The Hall-effect thruster is classed as a moderate [[specific impulse]] (1,600{{nbsp}}s) space propulsion technology and has benefited from considerable theoretical and experimental research since the 1960s.<ref>{{cite report|last=Hofer, Richard R.|title=Development and Characterization of High-Efficiency, High-Specific Impulse Xenon Hall Thrusters|work=NASA/CR—2004-21309|date=June 2004|publisher=NASA STI Program|hdl=2060/20040084644}}</ref>
* '''[[Heat shield]]''' – A heat shield is designed to protect an object from overheating by dissipating, reflecting, absorbing heat, or simply gradually burn and fall away from the aircraft, pulling the excess heat with it. The term is most often used in reference to [[exhaust heat management]] and to systems for dissipation of heat due to friction.
* '''[[Helicopter]]''' – is a type of [[rotorcraft]] in which [[Lift (force)|lift]] and [[thrust]] are supplied by horizontally-spinning [[Helicopter rotor|rotor]]s. This allows the helicopter to take off and land vertically, to [[hover (helicopter)|hover]], and to fly forward, backward and laterally. These attributes allow helicopters to be used in congested or isolated areas where [[fixed-wing aircraft]] and many forms of [[VTOL]] (Vertical TakeOff and Landing) aircraft cannot perform.
* '''[[Hypersonic speed#Classification of Mach regimes|High-hypersonic]]''' – 
* '''[[Hohmann transfer orbit]]''' – In [[orbital mechanics]], the Hohmann transfer orbit ({{IPAc-en|ˈ|h|oʊ|m|ə|n}}) is an [[elliptical orbit]] used to transfer between two [[circular orbit]]s of different radii around a central body in the same [[Plane (geometry)|plane]]. The Hohmann transfer often uses the lowest possible amount of [[propellant]] in traveling between these orbits, but [[bi-elliptic transfer]]s can use less in some cases.
* '''[[Hybrid rocket]]''' – A hybrid-propellant rocket is a [[rocket]] with a [[rocket motor]] that uses [[rocket propellants]] in two different phases: [[solid rocket propellant|one solid]] and the other either gas or [[liquid rocket propellant|liquid]]. The hybrid rocket concept can be traced back to at least the 1930s.<ref>{{cite web |title=GIRD-09 |publisher=Encyclopedia Astronautix |url=http://www.astronautix.com/g/gird-09.html |archive-url=https://web.archive.org/web/20161221091441/http://www.astronautix.com/g/gird-09.html |url-status=dead |archive-date=December 21, 2016 |access-date=June 25, 2017}}</ref>
* '''[[Hydrodynamics]]''' – In [[physics]] and [[engineering]], '''fluid dynamics'''  is a subdiscipline of [[fluid mechanics]] that describes the flow of [[fluid]]s—[[liquid]]s and [[gas]]es.  It has several subdisciplines, including [[aerodynamics]] (the study of air and other gases in motion) and '''hydrodynamics''' (the study of liquids in motion).  Fluid dynamics has a wide range of applications, including calculating [[force]]s and [[moment (physics)|moment]]s on [[aircraft]], determining the [[mass flow rate]] of [[petroleum]] through [[pipeline transport|pipelines]], [[weather forecasting|predicting weather pattern]]s, understanding [[nebula]]e in [[interstellar space]] and [[Nuclear weapon design|modelling fission weapon detonation]].
* '''[[Hydrostatics]]''' – '''Fluid statics''' or '''hydrostatics''' is the branch of [[fluid mechanics]] that studies the condition of the equilibrium of a floating body and submerged body "[[fluid]]s at [[hydrostatic equilibrium]]<ref name="en.wikibooks.org"/> and the pressure in a fluid, or exerted by a fluid, on an immersed body".<ref name="MW dictionary def"/>  It encompasses the study of the conditions under which fluids are at rest in [[Mechanical equilibrium|stable equilibrium]] as opposed to [[fluid dynamics]], the study of fluids in motion. Hydrostatics is a subcategory of fluid statics, which is the study of all fluids, both compressible or incompressible, at rest.
* '''[[Hyperbolic partial differential equation]]''' – In [[mathematics]], a hyperbolic partial differential equation of order <math>n</math> is a [[partial differential equation]] (PDE) that, roughly speaking, has a well-posed [[initial value problem]] for the first <math>n-1</math> derivatives. More precisely, the [[Cauchy problem]] can be locally solved for arbitrary initial data along any non-characteristic [[hypersurface]].  Many of the equations of [[mechanics]] are hyperbolic, and so the study of hyperbolic equations is of substantial contemporary interest. The model hyperbolic equation is the [[wave equation]].  In one spatial dimension, this is
::<math>\frac{\partial^2 u}{\partial t^2} = c^2 \frac{\partial^2 u}{\partial x^2} </math>
:The equation has the property that, if ''u'' and its first time derivative are arbitrarily specified initial data on the line {{nowrap|1=''t'' = 0}} (with sufficient smoothness properties), then there exists a solution for all time ''t''.
* '''[[Hypersonic speed]]''' – In [[aerodynamics]], a hypersonic speed is one that greatly exceeds the [[speed of sound]], often stated as starting at speeds of [[speed of sound|Mach]] 5 and above.<ref>{{cite book | title=Atmospheric Flight in the Twentieth Century | editor=Galison, P. |editor2=Roland, A. | publisher=Springer | year=2000 | url=https://books.google.com/books?id=qfrOBgAAQBAJ | isbn=978-94-011-4379-0 | page=90}}</ref>  The precise [[Mach number]] at which a craft can be said to be flying at hypersonic speed varies, since individual physical changes in the airflow (like molecular [[Dissociation (chemistry)|dissociation]] and [[ionization]]) occur at different speeds; these effects collectively become important around Mach 5–10. The hypersonic regime can also be alternatively defined as speeds where specific heat capacity changes with the temperature of the flow as kinetic energy of the moving object is converted into heat.<ref>{{cite web
|url=https://www.grc.nasa.gov/WWW/BGH/realspec.html
|title=Specific Heat Capacity, Calorically Imperfect Gas
|publisher=[[NASA]]
|access-date=2019-12-27
}}</ref>
* '''[[Hypoxia (medical)|Hypoxia]]''' – is a condition<ref>{{Cite book|title=Common Surgical Diseases|last1=Samuel|first1=Jacob|last2=Franklin|first2=Cory|date=2008|location= New York|publisher=Springer|isbn=978-0387752457|pages=391–94|language=en|doi=10.1007/978-0-387-75246-4_97}}</ref>  in which the body or a region of the body is deprived of adequate [[oxygen]] supply at the [[tissue (biology)|tissue]] level. Hypoxia may be classified as either ''generalized'', affecting the whole body, or ''local'', affecting a region of the body.<ref>Das, K. K., Honnutagi, R., Mullur, L., Reddy, R. C., Das, S., Majid, D. S. A., & Biradar, M. S. (2019). "Heavy metals and low-oxygen microenvironment{{snd}}its impact on liver metabolism and dietary supplementation". In ''Dietary Interventions in Liver Disease''. pp. 315–32. Academic Press.</ref> Although hypoxia is often a [[pathological]] condition, variations in arterial oxygen concentrations can be part of the normal physiology, for example, during [[hypoventilation training]] or strenuous physical exercise.

== I ==

* '''[[Specific impulse|Impulse]]''' – Specific impulse (usually abbreviated ''I''<sub>sp</sub>) is a measure of how efficiently a [[rocket engine|rocket]] uses propellant or a [[jet engine]] uses fuel. For engines whose reaction mass is only the fuel they carry, specific impulse is exactly proportional to exhaust gas velocity.
* '''[[Indicated airspeed]]''' – (IAS), is the [[airspeed]] read directly from the [[airspeed indicator]] (ASI) on an aircraft, driven by the [[pitot-static system]].<ref name="LJC3.9">Clancy, L.J. (1975), ''Aerodynamics'', Section 3.9, Pitman Publishing Limited, London. {{ISBN|0-273-01120-0}}</ref> It uses the difference between total pressure and static pressure, provided by the system, to either mechanically or electronically measure [[dynamic pressure]]. The dynamic pressure includes terms for both density and airspeed. Since the airspeed indicator cannot know the density, it is by design calibrated to assume the [[International Standard Atmosphere|sea level standard]] atmospheric density when calculating airspeed. Since the actual density will vary considerably from this assumed value as the aircraft changes altitude, IAS varies considerably from [[true airspeed]] (TAS), the relative velocity between the aircraft and the surrounding air mass. [[Calibrated airspeed]] (CAS) is the IAS corrected for instrument and [[position error]].<ref name="LJC3.9" />  An aircraft's indicated airspeed in knots is typically abbreviated ''KIAS'' for "[[Knot (unit)|Knots]]-Indicated Air Speed" (vs. ''KCAS'' for [[calibrated airspeed]] and ''KTAS'' for [[true airspeed]]).
* '''[[Instrument landing system]]''' – In [[aviation]], the instrument landing system (ILS) is a [[radio navigation]] system that provides short-range guidance to [[aircraft]] to allow them to approach a [[runway]] at night or in bad weather. In its original form, it allows an aircraft to approach until it is {{convert|200|feet}} over the ground, within a {{convert|1/2|mi|m}} of the runway. At that point the runway should be visible to the pilot; if it is not, they perform a [[missed approach]]. Bringing the aircraft this close to the runway dramatically improves the weather conditions in which a safe [[landing]] can be made. Later versions of the system, or "categories", have further reduced the minimum altitudes.
* '''[[Interplanetary Transport Network]]''' – (ITN)<ref name=Ross-SA-2006>{{cite journal |last=Ross |url=http://www2.esm.vt.edu/~sdross/papers/AmericanScientist2006.pdf |first=S. D. |date=2006 |doi=10.1511/2006.59.994 |title=The Interplanetary Transport Network |journal=[[American Scientist]] |volume=94 |issue=3 |pages=230–237 |access-date=2021-09-30 |archive-date=2013-10-20 |archive-url=https://web.archive.org/web/20131020185722/http://www2.esm.vt.edu/~sdross/papers/AmericanScientist2006.pdf |url-status=dead }}</ref> is a collection of [[gravitation]]ally determined pathways through the [[Solar System]] that require very little [[energy]] for an object to follow.  The ITN makes particular use of [[Lagrange points]] as locations where [[trajectories]] through [[Outer space|space]] can be redirected using little or no energy. These points have the peculiar property of allowing objects to [[orbit]] around them, despite lacking an object to orbit. While it would use little energy, transport along the network would take a long time.<ref>{{Cite web |url=http://www2.esm.vt.edu/~sdross/superhighway/description.html |title=The Interplanetary Superhighway; Shane Ross; Virginia Tech. |access-date=2021-09-30 |archive-date=2019-06-15 |archive-url=https://web.archive.org/web/20190615004515/http://www2.esm.vt.edu/~sdross/superhighway/description.html |url-status=dead }}</ref>
* '''[[Interplanetary travel]]''' – '''Interplanetary spaceflight''' or interplanetary travel is the [[Human spaceflight|crewed]] or [[Uncrewed spacecraft|uncrewed]] travel between [[stars]] and [[planets]], usually within a single [[planetary system]].<ref>Interplanetary Flight: an introduction to astronautics. London: Temple Press, [[Arthur C. Clarke]], 1950</ref>
* '''[[Interstellar travel]]''' – refers to the currently theoretical idea of [[interstellar probe]]s or crewed spacecraft moving between [[star]]s or [[planetary system]]s in a galaxy. Interstellar travel would be much more difficult than [[interplanetary spaceflight]]. Whereas the distances between the [[planet]]s in the [[Solar System]] are less than 30 [[astronomical unit]]s (AU), the distances between stars are typically hundreds of thousands of AU, and usually expressed in [[light-year]]s. Because of the vastness of those distances, practical interstellar travel based on known physics would need to occur at a high percentage of the [[speed of light]]; even so, travel times would be long, at least decades and perhaps millennia or longer.<ref name="Mauldin">{{Cite book|last=Mauldin|first=John H.|url=https://archive.org/details/prospectsforinte0000maul|url-access=registration|quote=Interstellar travel.|title=Prospects for interstellar travel|date=May 1992|publisher=Published for the American Astronautical Society by Univelt|language=en}}</ref>
* '''[[Ion thruster]]''' – An ion thruster, '''ion drive''', or '''ion engine''' is a form of [[electrically powered spacecraft propulsion|electric propulsion]] used for [[spacecraft propulsion]]. It creates [[thrust]] by accelerating [[ion]]s using [[electricity]].
* '''[[ISRO]]''' – The '''Indian Space Research Organisation'''{{efn|[[ISO 15919]]: {{transliteration|hi|ISO|Bhāratīya Antarikṣ Anusandhān Saṅgaṭhan}}  {{transliteration|hi|ISO|Bhāratīya Antrikṣ Anusandhān Saṅgaṭhan}}}} ('''ISRO''' {{IPAc-en|ˈ|ɪ|s|r|oʊ}}) or ([[International Alphabet of Sanskrit Transliteration|IAST]] : '''Bhāratīya Antrikṣ Anusandhān Saṅgaṭhan''') is the [[Government space agency|national space agency]] of [[India]], headquartered in [[Bengaluru]]. It operates under the [[Department of Space]] (DOS) which is directly overseen by the [[Prime Minister of India]], while [[Chairman of ISRO]] acts as executive of DOS as well. ISRO is the primary agency in India to perform tasks related to space based applications, [[space exploration]] and development of related technologies.<ref name="isro_aboutus">{{cite web|url = http://www.isro.gov.in/about-isro/vision-and-mission-statements|title = ISRO – Vision and Mission Statements|publisher = ISRO|access-date = 27 August 2015|archive-url = https://web.archive.org/web/20150904080053/http://www.isro.gov.in/about-isro/vision-and-mission-statements|archive-date = 4 September 2015|url-status = live}}</ref> It is one of six government space agencies in the world which possess full launch capabilities, deploy [[Cryogenic rocket engine|cryogenic engines]], launch [[List of Solar System probes|extraterrestrial missions]] and operate large fleets of artificial satellites.<ref name="Cryo14">{{Cite news|author=TE Narasimhan|date=2014-01-07|title=ISRO on cloud nine as India joins "cryo club"|url=https://wap.business-standard.com/article/current-affairs/isro-on-cloud-nine-as-india-joins-cryo-club-114010700023_1.html|newspaper=Business Standard|location=Chennai|access-date=2021-03-12}}</ref><ref>{{cite book|last1=Harvey|first1=Brian|last2=Smid|first2=Henk H. F.|last3=Pirard|first3=Theo|title=Emerging Space Powers: The New Space Programs of Asia, the Middle East and South-America|url=https://books.google.com/books?id=XD1ZaYbiWwMC&pg=PA144|year=2011|publisher=Springer Science & Business Media|isbn=978-1-4419-0874-2|pages=144–|access-date=14 April 2019|archive-date=12 October 2017|archive-url=https://web.archive.org/web/20171012092733/https://books.google.com/books?id=XD1ZaYbiWwMC|url-status=live}}</ref>{{efn|[[CNSA]] (China), [[European Space Agency|ESA]] (most of Europe), ISRO, (India), [[JAXA]] (Japan), [[NASA]] (United States) and [[Roscosmos]] (Russia) are space agencies with full launch capabilities.}}

== J ==

* '''[[Jet engine]]''' – is a type of [[reaction engine]] discharging a fast-moving [[jet (fluid)|jet]] that generates [[thrust]] by [[jet propulsion]].

== K ==

* '''[[Keel effect]]''' – In [[aeronautics]], the keel effect (also known as the ''pendulum effect'' or ''pendulum stability''<ref name="Hitchens2015">{{cite book|last1=Hitchens|first1=Frank|title=The Encyclopedia of Aerodynamics|date=2015|publisher=Andrews UK Limited|isbn=9781785383250|url=https://books.google.com/books?id=Zjv0CgAAQBAJ&q=keel+effect&pg=PT369|accessdate=13 September 2017|language=en}}</ref>) is the result of the sideforce-generating surfaces being above (or below) the [[center of mass]] (which coincides with the [[center of gravity (aircraft)|center of gravity]]) in an aircraft. Along with [[dihedral (aeronautics)|dihedral]], [[sweepback]], and [[weight distribution]], keel effect is one of the four main design considerations in aircraft [[Flight dynamics (aircraft)#Lateral modes|lateral stability]].<ref name="FAA2017">{{cite book|last1=Administration|first1=Federal Aviation|title=Pilot's Handbook of Aeronautical Knowledge|date=2017|publisher=Skyhorse Publishing, Inc.|isbn=9781510726185|url=https://books.google.com/books?id=L5TfDQAAQBAJ&q=%22Keel+effect%22&pg=PT266|accessdate=13 September 2017|language=en}}</ref>
* '''[[Kepler's laws of planetary motion]]''' – In [[astronomy]], '''Kepler's laws of planetary motion''', published by [[Johannes Kepler]] between 1609 and 1619, describe the orbits of [[planet]]s around the [[Sun]]. The laws modified the [[Copernican heliocentrism|heliocentric theory]] of [[Nicolaus Copernicus]], replacing its circular [[orbit]]s and [[epicycles]] with elliptical trajectories, and explaining how planetary velocities vary. The three laws state that:
:# The orbit of a planet is an [[ellipse]] with the Sun at one of the two foci.
:# A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
:# The square of a planet's [[orbital period]] is proportional to the cube of the length of the [[Semi-major and semi-minor axes|semi-major axis]] of its orbit.

:The elliptical orbits of planets were indicated by calculations of the orbit of [[Mars]]. From this, Kepler inferred that other bodies in the [[Solar System]], including those farther away from the Sun, also have elliptical orbits. The second law helps to establish that when a planet is closer to the Sun, it travels faster. The third law expresses that the farther a planet is from the Sun, the slower its orbital speed, and vice versa.

:[[Isaac Newton]] showed in 1687 that relationships like Kepler's would apply in the Solar System as a consequence of his own [[Newton's laws of motion|laws of motion]] and [[Newton's law of universal gravitation|law of universal gravitation]].
* '''[[Kessler syndrome]]''' – (also called the '''Kessler effect''',<ref name="aaRtY">{{cite web |url=http://articles.cnn.com/2002-05-03/tech/orbit.debris_1_low-earth-orbits-space-junk-international-space-station?_s=PM:TECH |title=Scientist: Space weapons pose debris threat| first= Richard |last= Stenger |website= [[CNN]].com |date=2002-05-03 |access-date= 2011-03-17 |url-status=dead |archive-url= https://web.archive.org/web/20120930100948/http://articles.cnn.com/2002-05-03/tech/orbit.debris_1_low-earth-orbits-space-junk-international-space-station?_s=PM:TECH |archive-date=2012-09-30}}</ref><ref name="h8L67">{{cite web|url=https://www.theatlantic.com/past/docs/issues/98jul/junk.htm |title=The Danger of Space Junk – 98.07 |work= [[The Atlantic]]| first= Steve| last= Olson| date= July 1998| via=TheAtlantic.com |access-date=2020-06-18}}</ref> '''collisional cascading''', or '''ablation cascade'''), proposed by [[NASA]] scientist [[Donald J. Kessler]] in 1978, is a theoretical scenario in which the density of objects in [[low Earth orbit]] (LEO) due to [[space pollution]] is high enough that collisions between objects could cause a cascade in which each collision generates [[space debris]] that increases the likelihood of further collisions.<ref name="kessler">{{cite journal | first1= Donald J.| last1= Kessler |first2= Burton G.| last2= Cour-Palais | title=Collision Frequency of Artificial Satellites: The Creation of a Debris Belt | journal=Journal of Geophysical Research | year=1978 | volume=83 | issue= A6 | pages=2637–2646 | doi=10.1029/JA083iA06p02637|bibcode = 1978JGR....83.2637K}}</ref> One implication is that the distribution of debris in orbit could render space activities and the use of [[satellite]]s in specific orbital ranges difficult for many generations.<ref name="kessler" />
* '''[[Kinetic energy]]''' – In [[physics]], the '''kinetic energy''' of an object is the [[energy]] that it possesses due to its [[motion (physics)|motion]].<ref>{{cite book | title=Textbook of Engineering Physics (Part I) | first1=Mahesh C. | last1=Jain | year=2009 | isbn=978-81-203-3862-3 | page=9 | publisher=PHI Learning Pvt. | url=https://books.google.com/books?id=wKeDYbTuiPAC | access-date=2018-06-21 | archive-date=2020-08-04 | archive-url=https://web.archive.org/web/20200804012822/https://books.google.com/books?id=wKeDYbTuiPAC | url-status=live }}, [https://books.google.com/books?id=wKeDYbTuiPAC&q=kinetic&pg=PA9 Chapter 1, p. 9] {{Webarchive|url=https://web.archive.org/web/20200804012414/https://books.google.com/books?id=wKeDYbTuiPAC&pg=PA9#v=snippet&q=kinetic&f=false |date=2020-08-04 }}</ref>  It is defined as the [[work (physics)|work]] needed to accelerate a body of a given mass from rest to its stated [[velocity]]. Having gained this energy during its [[acceleration]], the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body when decelerating from its current speed to a state of rest.  In [[classical mechanics]], the kinetic energy of a non-rotating object of [[mass]] ''m'' traveling at a [[speed]] ''v'' is <math display="inline"> \frac{1}{2}mv^2</math>. In [[Special relativity|relativistic mechanics]], this is a good approximation only when ''v'' is much less than the [[speed of light]].
* '''[[Kite]]''' – is a [[tether]]ed [[heavier than air flight|heavier-than-air]] or lighter-than-air craft with [[wing]] surfaces that react against the air to create [[Lift (force)|lift]] and [[Drag (physics)|drag]] forces.<ref>[[Kytoon]]</ref> A kite consists of wings, tethers and anchors. Kites often have a bridle and tail to guide the face of the kite so the wind can lift it.<ref>{{Cite book|title = The Magnificent Book of Kites: Explorations in Design, Construction, Enjoyment & Flight|last = Eden|first = Maxwell|publisher = Sterling Publishing Company, Inc.|year = 2002|isbn = 9781402700941|location = New York|pages = 18}}</ref> Some kite designs don't need a bridle; [[box kite]]s can have a single attachment point. A kite may have fixed or moving anchors that can balance the kite. One technical definition is that a kite is “a collection of tether-coupled wing sets“.<ref>{{cite web|url=http://www.energykitesystems.net/akiteis.html|title=What is a kite? A kite is ________. Definition of "kite" in the world.}}</ref> The name derives from its resemblance to a hovering [[kite (bird)|bird]].<ref>{{cite web|url=https://www.etymonline.com/word/kite|title=Etymology online}}</ref>
* '''[[Kutta condition]]''' – is a principle in steady-flow [[fluid dynamics]], especially [[aerodynamics]], that is applicable to solid bodies with sharp corners, such as the [[trailing edge]]s of [[airfoil]]s.  It is named for [[Germany|German]] [[mathematician]] and aerodynamicist [[Martin Kutta]].

:Kuethe and Schetzer state the Kutta condition as follows:<ref>A.M. Kuethe and J.D. Schetzer (1959) Foundations of Aerodynamics, 2nd edition, John Wiley & Sons ISBN 0-471-50952-3</ref>{{rp|§ 4.11}}
::A body with a sharp trailing edge which is moving through a fluid will create about itself a [[circulation (fluid dynamics)|circulation]] of sufficient strength to hold the rear [[stagnation point]] at the trailing edge.

:In fluid flow around a body with a sharp corner, the Kutta condition refers to the flow pattern in which fluid approaches the corner from above and below, meets at the corner, and then flows away from the body. None of the fluid flows around the sharp corner.

:The Kutta condition is significant when using the [[Kutta–Joukowski theorem]] to calculate the lift created by an airfoil with a sharp trailing edge. The value of [[circulation (fluid dynamics)|circulation]] of the flow around the airfoil must be that value that would cause the Kutta condition to exist.
* '''[[Kutta–Joukowski theorem]]''' – is a fundamental theorem in [[aerodynamics]] used for the calculation of lift of an [[airfoil]] and any two-dimensional bodies including circular cylinders translating into a uniform fluid at a constant speed large enough so that the flow seen in the body-fixed frame is steady and unseparated. The theorem relates the [[lift (force)|lift]] generated by an airfoil to the speed of the airfoil through the fluid, the density of the fluid and the [[circulation (fluid dynamics)|circulation]] around the airfoil. The circulation is defined as the line integral around a closed-loop enclosing the airfoil of the component of the velocity of the fluid [[tangent]] to the loop.<ref>{{cite book |last=Anderson |first=J. D. Jr. |title=Introduction to Flight |chapter=Pressure, Temperature, and Density Altitudes |publisher=McGraw-Hill |location=New York |edition=3rd |year=1989 |isbn=0-07-001641-0 |pages=100–103 }}</ref> It is named after [[Martin Kutta]] and [[Nikolay Zhukovsky (scientist)|Nikolai Zhukovsky]] (or Joukowski) who first developed its key ideas in the early 20th century. Kutta–Joukowski theorem is an [[Inviscid flow|inviscid theory]], but it is a good approximation for real viscous flow in typical aerodynamic applications.<ref>{{cite journal |last1=Liu |first1=L. Q. |last2=Zhu |first2=J. Y. |last3=Wu |first3=J. Z. |title=Lift and drag in two-dimensional steady viscous and compressible flow |journal=Journal of Fluid Mechanics |year=2015 |volume=784 |pages=304–341 |doi=10.1017/jfm.2015.584 |bibcode=2015JFM...784..304L |s2cid=125643946 }}</ref>

== L ==

* '''[[Lander (spacecraft)|Lander]]''' – [[spacecraft]] designed to soft-land intact or almost undamaged on the surface of a [[celestial body]] and eventually take-off from it
* '''[[Landing]]''' – is the last part of a [[flight]], where an [[aircraft]], or [[spacecraft]] returns to the ground. When the flying object returns to water, the process is called '''alighting''', although it is commonly called "landing", "touchdown"{{ref|td|a}} or "[[Splashdown (spacecraft landing)|splashdown]]" as well. A normal aircraft flight would include several parts of flight including [[taxiing|taxi]], [[takeoff]], [[climb (aeronautics)|climb]], [[Cruise (flight)|cruise]], [[descent (aircraft)|descent]] and landing.
* '''[[Landing gear]]''' – is the undercarriage of an [[aircraft]] or [[spacecraft]] and may be used for either [[takeoff]] or [[landing]]. For aircraft it is generally needed for both.  Also, for aircraft, the landing gear supports the craft when it is not flying, allowing it to take off, land, and taxi without damage. Wheeled landing gear is the most common, with [[ski]]s or [[Seaplane|floats]] needed to operate from snow/ice/water and skids for vertical operation on land. Faster aircraft have retractable undercarriages, which fold away during flight to reduce [[drag (physics)|drag]].
* '''[[Lagrangian mechanics]]''' – Introduced by the Italian-French mathematician and astronomer [[Joseph-Louis Lagrange]] in 1788, '''Lagrangian mechanics''' is a formulation of [[classical mechanics]] and is founded on the [[principle of least action|stationary action principle]].

:Lagrangian mechanics defines a mechanical system to be a pair <math>(M,L)</math> of a [[configuration space (physics)|configuration space]] <math>M</math> and a smooth function <math>L = L(q,v,t)</math> called ''Lagrangian''. By convention, <math>L = T - V,</math> where <math>T</math> and <math>V</math> are the [[Kinetic energy|kinetic]] and [[Potential energy|potential]] energy of the system, respectively. Here <math>q \in M,</math> and <math>v</math> is the velocity vector at <math>q</math> <math>(v</math> is tangential to <math>M).</math> (For those familiar with [[tangent bundle]]s, <math>L : TM \times \mathbb{R}_t \to \mathbb{R},</math> and <math>v\in T_qM).</math>

:Given the time instants <math>t_1</math> and <math>t_2,</math> Lagrangian mechanics postulates that a smooth path <math>x_0: [t_1,t_2] \to M</math> describes the time evolution of the given system if and only if <math>x_0</math> is a ''stationary point'' of the [[Action (physics)|action functional]]

::<math>
{\cal S}[x]\, \stackrel{\text{def}}{=}\, \int^{t_2}_{t_1} L(x(t),{\dot x}(t),t)\, dt.
</math>

:If <math>M</math> is an open subset of <math>\mathbb{R}^n</math> and <math>t_1,</math> <math>t_2</math> are finite, then the smooth path <math>x_0</math> is a stationary point of <math>{\cal S}</math> if all its directional derivatives at <math>x_0</math> vanish, i.e., for every smooth <math>\delta : [t_1,t_2] \to \mathbb{R}^n,</math>

:<math>
\delta {\cal S}\ \stackrel{\text{def}}{=}\ \frac{d}{d\varepsilon}\Biggl|_{\varepsilon=0} {\cal S}\left[x_0+\varepsilon \delta\right] = 0.
</math>

:The function <math>\delta(t)</math> on the right-hand side is called ''perturbation'' or ''[[virtual displacement]]''. The directional derivative <math>\delta {\cal S}</math> on the left is known as ''variation'' in physics and [[Gateaux derivative]] in mathematics.

:Lagrangian mechanics has been extended to allow for non-[[Conservative force|conservative]] forces.
* '''[[Lagrangian point]]''' – In [[celestial mechanics]], the Lagrange points {{IPAc-en|l|ə|ˈ|ɡ|r|ɑː|n|dʒ}} (also '''Lagrangian points''', '''L-points''', or '''libration points''') are points near two large [[orbit]]ing bodies. Normally, the two objects exert an unbalanced gravitational force at a point, altering the orbit of whatever is at that point. At the Lagrange points, the [[gravitation]]al forces of the two large bodies and the [[centrifugal force]] balance each other.<ref>{{Cite web|url=https://scienceworld.wolfram.com/physics/LagrangePoints.html|title=Lagrange Points|first=Eric|last=Weisstein|website=Eric Weisstein's World of Physics}}</ref> This can make Lagrange points an excellent location for satellites, as few [[Orbital station-keeping|orbit corrections]] are needed to maintain the desired orbit. Small objects placed in orbit at Lagrange points are in equilibrium in at least two directions relative to the [[center of mass]] of the large bodies.
* '''[[Laser broom]]''' – is a proposed ground-based [[laser]] [[beam-powered propulsion]] system whose purpose is to sweep [[space debris]] out of the path of other [[artificial satellites]] such as the [[International Space Station]]. It would heat one side of an object enough to change its orbit and make it hit the atmosphere sooner. Space researchers have proposed that a laser broom may help mitigate [[Kessler syndrome]], a theoretical runaway cascade of collision events between orbiting objects.<ref>Dr Claude Phipps (2011). "Removing Orbital Debris with Lasers". Advances in Space Research. 49 (9): 1283–1300. arXiv:1110.3835. Bibcode:2012AdSpR..49.1283P. doi:10.1016/j.asr.2012.02.003.</ref>  Space-based laser broom systems using a laser mounted on a satellite or space station have also been proposed.<ref name="7BFkR">{{Cite journal|date=2014-08-01|title=Cleaning space debris with a space-based laser system|journal=Chinese Journal of Aeronautics|language=en|volume=27|issue=4|pages=805–811|doi=10.1016/j.cja.2014.05.002|issn=1000-9361|doi-access=free|last1=Shen|first1=Shuangyan|last2=Jin|first2=Xing|last3=Hao|first3=Chang|bibcode=2014ChJAn..27..805S }}</ref><ref name="w4XYT">{{Cite journal|date=2018-02-01|title=Impacts of orbital elements of space-based laser station on small scale space debris removal|url=https://www.sciencedirect.com/science/article/abs/pii/S0030402617312068|journal=Optik|language=en|volume=154|pages=83–92|doi=10.1016/j.ijleo.2017.10.008|issn=0030-4026|last1=Wen|first1=Quan|last2=Yang|first2=Liwei|last3=Zhao|first3=Shanghong|last4=Fang|first4=Yingwu|last5=Wang|first5=Yi|last6=Hou|first6=Rui|bibcode=2018Optik.154...83W}}</ref><ref name="DUUkb">{{Cite web|last1=Lin|last2=Singer|date=February 15, 2018|title=Is China's space laser for real?|url=https://www.popsci.com/china-space-laser/|access-date=2021-04-10|website=Popular Science|language=en-US}}</ref><ref name="JkyEc">{{Cite magazine|last=Venton|first=Danielle|date=May 12, 2015|title=The Mad Plan to Clean Up Space Junk With a Laser Cannon|language=en-us|magazine=Wired|url=https://www.wired.com/2015/05/laser-cannon-space-debris/|access-date=2021-04-10|issn=1059-1028}}</ref>
* '''[[Neptec Design Group#Laser Camera System|Laser Camera System]]''' – (LCS), is short-range, high precision autosynchronous triangulation scanner. The camera uses a laser to measure the distance between itself and points on a target and is able to create a three-dimensional representation of the area it has scanned.
* '''[[Latus rectum]]''' – is the [[Chord (geometry)|chord]] parallel to the directrix and passing through a focus; its half-length is the semi-latus rectum ({{math|''ℓ''}}).
* '''[[Launch window]]''' – In the context of [[spaceflight]], launch period is the collection of days and '''launch window''' is the time period on a given day during which a particular [[rocket]] must be launched in order to reach its intended target.<ref>{{cite web|last1=Walsh|first1=Kris|title=Launch Period vs. Launch Window|url=https://genesismission.jpl.nasa.gov/educate/scimodule/kriswalshsoundfiles/launch_period.html|website=Genesis Mission|publisher=NASA JPL|access-date=3 May 2018}}</ref><ref>{{cite report|last1=Sergeyevsky|first1=Andrey|title=Interplanetary Mission Design Handbook, Volume I, Part 2|publisher=NASA JPL|ref=JPL PUBLICATION 82-43|date=September 15, 1983|citeseerx=10.1.1.693.6602}}</ref> If the rocket is not launched within a given window, it has to wait for the window on the next day of the period.<ref>{{Cite web |url=https://www.nasa.gov/missions/highlights/schedule101.html |title=What is a launch window? |access-date=2021-10-08 |archive-date=2023-04-11 |archive-url=https://web.archive.org/web/20230411124048/https://www.nasa.gov/missions/highlights/schedule101.html |url-status=dead }}</ref> Launch periods and launch windows are very dependent on both the rocket's capability and the orbit to which it is going.<ref>{{cite web|title=Introduction to the GMAT Software|url=https://indico.esa.int/indico/event/111/session/2/material/0/0.pdf|publisher=NASA Goddard Space Flight Center|access-date=3 May 2018|date=Oct 29, 2014|archive-date=3 May 2018|archive-url=https://web.archive.org/web/20180503111409/https://indico.esa.int/indico/event/111/session/2/material/0/0.pdf|url-status=dead}}</ref><ref>{{cite web|title=Document Requirements Description|url=http://emits.sso.esa.int/emits-doc/ALCATEL/EXM-MS-RS-ESA-00010_ExoMarsDocumentRequirementsDiscription.pdf|website=ExoMars Project|publisher=European Space Agency|access-date=3 May 2018|date=16 July 2007}}</ref>
* '''[[Leading edge]]''' – The leading edge of an [[airfoil]] surface such as a [[wing]] is its foremost edge and is therefore the part which first meets the oncoming air.<ref name="Craneb">Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 305. Aviation Supplies & Academics, 1997. {{ISBN|1-56027-287-2}}</ref><ref name=Kumar>{{cite book |title=An Illustrated Dictionary of Aviation |last=Kumar |first=Bharat |year=2005|publisher= McGraw Hill|location=New York |isbn=0-07-139606-3}}</ref>
* '''[[Lift (force)|Lift]]''' – 
* '''[[Lift coefficient]]''' – is a [[Dimensionless quantity|dimensionless]] [[coefficient]] that relates the [[Lift (force)|lift]] generated by a [[lifting body]] to the [[fluid density]] around the body, the [[fluid velocity]] and an associated reference area. A lifting body is a [[foil (fluid mechanics)|foil]] or a complete foil-bearing body such as a [[fixed-wing aircraft]]. ''C''<sub>L</sub> is a function of the angle of the body to the flow, its [[Reynolds number]] and its [[Mach number]]. The lift coefficient ''c''<sub>l</sub> refers to the dynamic lift characteristics of a [[two-dimensional]] foil section, with the reference area replaced by the foil [[Chord (aircraft)|chord]].<ref name="Clancy">{{cite book|last=Clancy|first=L. J.|title=Aerodynamics|year=1975|publisher=John Wiley & Sons|location=New York|at=Sections 4.15 & 5.4}}</ref><ref name="TWS1">[[Ira H. Abbott|Abbott, Ira H.]], and Doenhoff, Albert E. von: ''Theory of Wing Sections''. Section 1.2</ref>
* '''[[Lightcraft]]''' – The Lightcraft is a [[spacecraft|space-]] or [[aircraft|air-]][[vehicle]] driven by [[beam-powered propulsion]], the energy source powering the craft being external. It was conceptualized by aerospace engineering professor [[Leik Myrabo]] at [[Rensselaer Polytechnic Institute]] in 1976,<ref name="Myrabo 1976">
{{cite journal
 | author = Myrabo, L.N.
 | author-link = Leik Myrabo
 | date = 1976
 | title = MHD propulsion by absorption of laser radiation
 | journal = Journal of Spacecraft and Rockets
 | volume = 13
 | issue = 8
 | url = http://ayuba.fr/pdf/myrabo1976.pdf
 | doi = 10.2514/3.27919
 | pages=466–472
 | bibcode = 1976JSpRo..13..466M
 }}
</ref> who developed the concept further with working prototypes,<ref name="Myrabo 1st test">{{cite conference
 |last1=Myrabo |first1=Leik N.
 |last2=Messitt |first2=Donald G.
 |last3=Mead Jr. |first3=Franklin B.
 |title=Ground and flight tests of a laser propelled vehicle
 |date=January 1998
 |conference=36th AIAA Aerospace Sciences Meeting and Exhibit
 |location=Reno, NV
 |book-title=AIAA-98-1001
 |url=http://ayuba.fr/pdf/myrabo1998a.pdf
 |doi=10.2514/6.1998-1001
}}</ref> funded in the 1980s by the [[Strategic Defense Initiative]] organization, and the decade after by the ''Advanced Concept Division'' of the [[United States Air Force|US Air Force]] [[Air Force Research Laboratory|AFRL]], [[NASA]]'s [[Marshall Space Flight Center|MFSC]] and the [[Lawrence Livermore National Laboratory]].<ref name="Popular Mechanics 1995">{{cite magazine
 |last1=Pope |first1=Gregory T.
 |title=Fly by microwaves
 |date=September 1995
 |magazine=Popular Mechanics
 |pages=44–45
 |url=http://ayuba.fr/pdf/popmech1995.pdf
 }}</ref><ref name="Wired">{{cite magazine
 |last1=Demerjian |first1=Ave
 |title=Laser-powered aircraft are the future of flight. Maybe 
 |date=20 February 2009
 |magazine=Wired
 |url=https://www.wired.com/2009/02/beamed-energy-i/
 |access-date=2018-04-05
}}</ref><ref name="PopSci">{{cite web
 |last1=Hsu |first1=Jeremy
 |title=Laser-Powered Lightcraft 'At the Cusp of Commercial Reality'
 |date=29 July 2009
 |website=Popular Science
 |url=http://www.popsci.com/military-aviation-amp-space/article/2009-07/high-powered-lightcraft-experiments-hint-future-space-travel
 |access-date=2018-04-05
}}</ref>
* '''[[Lighter than air]]''' – A '''lifting gas''' or '''lighter than air gas''' is a gas that has a lower density than normal atmospheric gases and rises above them as a result. It is required for [[aerostats]] to create [[buoyancy]], particularly in [[aerostat|lighter-than-air aircraft]], which include [[balloon (aircraft)|free balloons]], [[moored balloon]]s, and [[airships]]. Only certain lighter than air gases are suitable as lifting gases. Dry air has a density of about 1.29&nbsp;g/L (gram per liter) at [[standard conditions for temperature and pressure]] (STP) and an average molecular mass of 28.97&nbsp;[[Molar mass|g/mol]],<ref>{{Cite web|url=http://www.engineeringtoolbox.com/molecular-mass-air-d_679.html|title=Air - Molecular Weight|website=www.engineeringtoolbox.com|language=en|access-date=2018-01-16}}</ref> and so lighter than air gases have a density lower than this.
* '''[[Liquid air cycle engine]]''' – (LACE), is a type of [[spacecraft propulsion]] engine that attempts to increase its efficiency by gathering part of its [[oxidizer]] from the [[Earth's atmosphere|atmosphere]]. A liquid air cycle engine uses [[liquid hydrogen]] (LH2) fuel to liquefy the air.
* '''[[Liquid fuel]]''' – Liquid fuels are combustible or energy-generating molecules that can be harnessed to create [[mechanical energy]], usually producing [[kinetic energy]]; they also must take the shape of their container. It is the fumes of liquid fuels that are flammable instead of the fluid.  Most liquid fuels in widespread use are derived from [[fossil fuels]]; however, there are several types, such as [[hydrogen fuel]] (for [[automotive]] uses), ethanol, and [[biodiesel]], which are also categorized as a liquid fuel. Many liquid fuels play a primary role in transportation and the economy.  Liquid fuels are contrasted with [[solid fuel]]s and [[gaseous fuel]]s.
* '''[[Liquid-propellant rocket]]''' – or '''liquid rocket''', utilizes a [[rocket engine]] that uses [[liquid rocket propellant|liquid propellants]]. Liquids are desirable because they have a reasonably high density and high [[Specific impulse|specific impulse (''I''<sub>sp</sub>)]]. This allows the volume of the propellant tanks to be relatively low. It is also possible to use lightweight centrifugal [[turbopump]]s to pump the [[rocket propellant]] from the tanks into the combustion chamber, which means that the propellants can be kept under low pressure. This permits the use of low-mass propellant tanks that do not need to resist the high pressures needed to store significant amounts of gases, resulting in a low [[mass ratio]] for the rocket.{{citation_needed|date=July 2019}}
* '''[[Liquid rocket propellant]]''' – The highest [[specific impulse]] chemical '''rockets''' use '''liquid propellants''' ([[liquid-propellant rocket]]s). They can consist of a single chemical (a '''monopropellant''') or a mix of two chemicals, called [[bipropellants]]. Bipropellants can further be divided into two categories; [[hypergolic propellant]]s, which ignite when the fuel and [[Oxidizing agent|oxidizer]] make contact, and non-hypergolic propellants which require an ignition source.<ref>{{cite book|title=Space Mission Analysis and Design|last1=Larson|first1=W.J.|last2=Wertz|first2=J.R.|date=1992|publisher=Kluver Academic Publishers|location=Boston}}</ref>
* '''[[Lithobraking]]''' – is a landing technique used by uncrewed space vehicles to safely reach the surface of a celestial body while reducing landing speed by impact with the body's surface. 
* '''[[Loiter (aeronautics)|Loiter]]''' – In [[aeronautics]] and [[aviation]], loiter is the phase of flight  consisting of flying over some small region.
* '''[[Low Earth orbit]]''' – (LEO), is an [[geocentric orbit|Earth-centered orbit]] close to the planet, often specified as an [[orbital period]] of 128 minutes or less (making at least 11.25 orbits per day) and an [[orbital eccentricity|eccentricity]] less than 0.25.<ref>{{Cite web|url=https://www.space-track.org/#/recent|title=Current Catalog Files|access-date=July 13, 2018|quote=LEO: Mean Motion > 11.25 & Eccentricity < 0.25|archive-date=June 26, 2018|archive-url=https://web.archive.org/web/20180626190758/https://www.space-track.org/#/recent|url-status=live}}</ref> Most of the artificial objects in [[outer space]] are in LEO, with an altitude never more than about one-third of the [[Earth radius|radius of the Earth]].<ref>{{Cite journal|last1=Sampaio|first1=Jarbas|last2=Wnuk|first2=Edwin|last3=Vilhena de Moraes|first3=Rodolpho|last4=Fernandes|first4=Sandro|date=2014-01-01|title=Resonant Orbital Dynamics in LEO Region: Space Debris in Focus|url=https://www.researchgate.net/publication/273597440|journal=Mathematical Problems in Engineering|volume=2014|page=Figure 1: Histogram of the mean motion of the cataloged objects|doi=10.1155/2014/929810|doi-access=free|access-date=2018-07-13|archive-date=2021-10-01|archive-url=https://web.archive.org/web/20211001030902/https://www.researchgate.net/publication/273597440_Resonant_Orbital_Dynamics_in_LEO_Region_Space_Debris_in_Focus|url-status=live}}</ref>
* '''[[Apollo Lunar Module|Lunar Module]]''' – The '''Apollo Lunar Module''', or simply '''Lunar Module''' ('''LM''' {{IPAc-en|ˈ|l|ɛ|m}}), originally designated the '''Lunar Excursion Module''' ('''LEM'''), was the [[Lunar lander]] [[spacecraft]] that was flown between [[lunar orbit]] and the Moon's surface during the [[United States|United States']] [[Apollo program]]. It was the first crewed spacecraft to operate exclusively in the airless vacuum of space, and remains the only crewed vehicle to land anywhere beyond Earth.
* '''[[Lunar space elevator]]''' – or '''lunar spacelift''', is a proposed transportation system for moving a mechanical climbing vehicle up and down a ribbon-shaped tethered cable that is set between the surface of the [[Moon]] "at the bottom" and a docking port suspended tens of thousands of kilometers above in space at the top.

== M ==

* '''[[Mach number]]''' – In [[fluid dynamics]], the Mach number is a [[dimensionless quantity]] representing the ratio of [[flow velocity]] past a [[Boundary (thermodynamic)|boundary]] to the local [[speed of sound]].<ref name="Young_et_al">{{cite book|last=Young|first=Donald F.|title=A Brief Introduction to Fluid Mechanics|year=2010|publisher=John Wiley & Sons|isbn=978-0-470-59679-1|edition=5|author2=Bruce R. Munson |author3=Theodore H. Okiishi |author4=Wade W. Huebsch |page=95}}</ref><ref name="Graebel">{{cite book|last=Graebel|first=W.P.|title=Engineering Fluid Mechanics|url=https://archive.org/details/engineeringfluid00grae|url-access=limited|year=2001|publisher=Taylor & Francis|isbn=978-1-56032-733-2 |page=[https://archive.org/details/engineeringfluid00grae/page/n29 16]}}</ref>
* '''[[Magnetic sail]]''' – or '''magsail''', is a proposed method of [[spacecraft propulsion]] which would use a static magnetic field to deflect [[charged particle]]s radiated by the [[Sun]] as a [[plasma (physics)|plasma]] wind, and thus impart momentum to accelerate the spacecraft.<ref>D. G. Andrews and R. Zubrin, "Magnetic Sails and Interstellar Travel", Paper IAF-88-553, 1988</ref><ref>[[Robert Zubrin|R. Zubrin]]. (1999) ''Entering Space: Creating a Spacefaring Civilization''. New York: Jeremy P. Tarcher/Putnam. {{ISBN|0-87477-975-8}}.</ref>   A magnetic sail could also thrust directly against planetary and solar [[magnetosphere]]s.
* '''[[Magnetoplasmadynamic thruster]]''' – A magnetoplasmadynamic (MPD) thruster ('''MPDT''') is a form of [[electrically powered spacecraft propulsion]] which uses the [[Lorentz force]] (the force on a charged particle by an electromagnetic field) to generate thrust. It is sometimes referred  to as Lorentz Force Accelerator (LFA) or (mostly in Japan) MPD arcjet.
* '''[[Mass]]''' – is both a [[physical property|property]] of a [[physical body]] and a [[measure (mathematics)|measure]] of its [[Inertia|resistance]] to [[acceleration]] (rate of change of [[velocity]] with respect to time) when a [[net force]] is applied.<ref>{{Cite web | url=http://dictionary.reference.com/browse/mass | title=The definition of mass}}</ref> An object's mass also determines the [[Force|strength]] of its [[gravitation]]al attraction to other bodies.  The [[SI base unit]] of mass is the [[kilogram]] (kg). In [[physics]], mass is not the same as [[weight]], even though mass is often determined by measuring the object's weight using a [[spring scale]], rather than [[Weighing scale#Balance scales|balance scale]] comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass. This is because weight is a force, while mass is the property that (along with gravity) determines the strength of this force.
* '''[[Mass driver]]''' – or '''electromagnetic catapult''', is a proposed method of [[non-rocket spacelaunch]] which would use a [[linear motor]] to [[Acceleration|accelerate]] and catapult [[Payload (air and space craft)|payload]]s up to high speeds.  All existing and contemplated mass drivers use coils of wire energized by electricity to make [[electromagnet]]s. Sequential firing of a row of electromagnets accelerates the payload along a path. After leaving the path, the payload continues to move due to [[momentum]].
* '''[[Mechanics of fluids]]''' – 
* '''[[Membrane mirror]]''' – 
* '''[[Metre per second]]''' – 
* '''[[Mini-magnetospheric plasma propulsion]]''' – 
* '''[[Moment of inertia]]''' – otherwise known as the '''mass moment of inertia''', '''angular mass''', '''second moment of mass''', or most accurately, '''rotational inertia''', of a [[rigid body]] is a quantity that determines the [[torque]] needed for a desired [[angular acceleration]] about a rotational axis, akin to how [[mass]] determines the [[force]] needed for a desired [[acceleration]]. It depends on the body's mass distribution and the axis chosen, with larger moments requiring more torque to change the body's rate of rotation.
* '''[[Momentum]]''' – In [[Newtonian mechanics]], '''linear momentum''', '''translational momentum''', or simply '''momentum''' is the product of the [[mass]] and [[velocity]] of an object. It is a [[Euclidean vector|vector]] quantity, possessing a magnitude and a direction. If {{math|''m''}} is an object's mass and {{math|'''v'''}} is its velocity (also a vector quantity), then the object's momentum {{math|'''p'''}} is

::<math>\mathbf{p} = m \mathbf{v}.</math>

:In the [[International System of Units]] (SI), the [[unit of measurement]] of momentum is the [[kilogram]] [[metre per second]] (kg⋅m/s), which is equivalent to the [[newton-second]].
* '''[[Momentum wheel]]''' – 
* '''[[Monopropellant rocket]]''' – or '''monochemical rocket''', is a [[rocket]] that uses a single [[chemical]] as its [[propellant]].
* '''[[Motion]]''' – In [[physics]], motion is the phenomenon in which an object changes its [[position (mathematics)|position]]. Motion is mathematically described in terms of [[Displacement (mathematics)|displacement]], [[distance]], [[velocity]], [[acceleration]], [[speed]], and [[time]]. The motion of a body is observed by attaching a [[frame of reference]] to an observer and measuring the change in position of the body relative to that frame with change in time. The branch of physics describing the motion of objects without reference to its cause is [[kinematics]]; the branch studying forces and their effect on motion is [[dynamics (mechanics)|dynamics]].
* '''[[Multistage rocket]]''' – or '''step rocket'''<ref>{{Cite web|title=Brief History of Rockets|url=https://www.grc.nasa.gov/www/k-12/TRC/Rockets/history_of_rockets.html}}</ref> is a [[launch vehicle]] that uses two or more [[rocket]] ''stages'', each of which contains its own [[Rocket engine|engines]] and [[Rocket propellant|propellant]]. A ''tandem'' or ''serial'' stage is mounted on top of another stage; a ''parallel'' stage is attached alongside another stage. The result is effectively two or more rockets stacked on top of or attached next to each other. Two-stage rockets are quite common, but rockets with as many as five separate stages have been successfully launched.

== N ==

* '''[[National Advisory Committee for Aeronautics|NACA]]''' – [[United States]] National Advisory Committee for Aeronautics, replaced by [[NASA]] in 1958.
* '''[[NASA]]''' – [[United States]] National Aeronautics and Space Administration.
* '''[[Navier–Stokes equations]]''' – In [[physics]], the Navier–Stokes equations({{IPAc-en|n|æ|v|ˈ|j|eː|_|s|t|əʊ|k|s}}) are certain [[partial differential equation]]s which describe the motion of [[viscous fluid]] substances, named after French engineer and physicist [[Claude-Louis Navier]] and Anglo-Irish physicist and mathematician [[Sir George Stokes, 1st Baronet|George Gabriel Stokes]].  They were developed over several decades of progressively building the theories, from 1822 (Navier) to 1842–1850 (Stokes).

:The Navier–Stokes equations mathematically express [[conservation of momentum]] and [[conservation of mass]] for [[Newtonian fluid]]s. They are sometimes accompanied by an [[equation of state]] relating [[pressure]], [[temperature]]  and [[density]].<ref>{{cite book |title=Understanding Aerodynamics: Arguing from the Real Physics |first=Doug |last=McLean |publisher=John Wiley & Sons |year=2012 |chapter=Continuum Fluid Mechanics and the Navier-Stokes Equations |pages=13&ndash;78 |isbn=9781119967514 |quote=The main relationships comprising the NS equations are the basic conservation laws for mass, momentum, and energy. To have a complete equation set we also need an equation of state relating temperature, pressure, and density... |chapter-url=https://books.google.com/books?id=UE3sxu28R0wC&pg=PA13 }}</ref> They arise from applying [[Newton's second law|Isaac Newton's second law]] to [[Fluid dynamics|fluid motion]], together with the assumption that the [[stress (mechanics)|stress]] in the fluid is the sum of a [[diffusion|diffusing]] [[viscosity|viscous]] term (proportional to the [[gradient]] of velocity) and a [[pressure]] term—hence describing ''viscous flow''. The difference between them and the closely related [[Euler equations (fluid dynamics)|Euler equations]] is that Navier–Stokes equations take viscosity into account while the Euler equations model only [[inviscid flow]]. As a result, the Navier–Stokes are a [[parabolic equation]] and therefore have better analytic properties, at the expense of having less mathematical structure (e.g. they are never [[completely integrable]]).
* '''[[Newton (unit)]]''' – The newton (symbol: '''N''') is the [[International System of Units]] (SI) [[SI derived unit|derived unit]] of [[force]]. It is named after [[Isaac Newton]] in recognition of his work on [[classical mechanics]], specifically [[Newton's laws of motion#Newton's second law|Newton's second law of motion]].

:A newton is defined as 1 kg⋅m/s{{sup|2}}, which is the force which gives a mass of 1 kilogram an acceleration of 1 metre per second, per second.
* '''[[Newton's law of universal gravitation]]''' – is usually stated as that every [[particle]] attracts every other particle in the universe with a [[force]] that is [[Proportionality (mathematics)#Direct proportionality|directly proportional]] to the product of their masses and [[Proportionality (mathematics)#Inverse proportionality|inversely proportional]] to the square of the distance between their centers.<ref group="note">It was shown separately that separated spherically symmetrical masses attract and are attracted [[Shell theorem|as if all their mass were concentrated at their centers]].</ref> The publication of the theory has become known as the "[[Unification (physics)|first great unification]]", as it marked the unification of the previously described phenomena of gravity on Earth with known astronomical behaviors.<ref>{{cite book|author=Fritz Rohrlich|title=From Paradox to Reality: Our Basic Concepts of the Physical World|url=https://books.google.com/books?id=3TqA1394OVcC&pg=PA28|date=25 August 1989|publisher=Cambridge University Press|isbn=978-0-521-37605-1|pages=28–}}</ref><ref>{{cite book|author=Klaus Mainzer|title=Symmetries of Nature: A Handbook for Philosophy of Nature and Science|url=https://books.google.com/books?id=QekhAAAAQBAJ&pg=PA8|date=2 December 2013|publisher=Walter de Gruyter|isbn=978-3-11-088693-1|pages=8–}}</ref><ref>{{Cite web|url=https://www.encyclopedia.com/science/science-magazines/physics-fundamental-forces-and-synthesis-theory|title=Physics: Fundamental Forces and the Synthesis of Theory &#124; Encyclopedia.com|website=www.encyclopedia.com}}</ref>

:This is a general [[physical law]] derived from [[empirical observation]]s by what [[Isaac Newton]] called [[inductive reasoning]].<ref>Isaac Newton: "In [experimental] philosophy particular propositions are inferred from the phenomena and afterwards rendered general by induction": "[[Philosophiae Naturalis Principia Mathematica|Principia]]", Book 3, General Scholium, at p.392 in Volume 2 of Andrew Motte's English translation published 1729.</ref> It is a part of [[classical mechanics]] and was formulated in Newton's work ''[[Philosophiæ Naturalis Principia Mathematica]]'' ("the ''Principia''"), first published on 5 July 1687. When Newton presented Book 1 of the unpublished text in April 1686 to the [[Royal Society]], [[Robert Hooke]] made a claim that Newton had obtained the inverse square law from him.

:In today's language, the law states that every [[Point particle|point]] [[mass]] attracts every other point mass by a [[force]] acting along the [[Line (mathematics)|line]] intersecting the two points. The force is [[Proportionality (mathematics)|proportional]] to the [[Product (mathematics)|product]] of the two masses, and inversely proportional to the [[Square (algebra)|square]] of the distance between them.<ref name=Newton1>Proposition 75, Theorem 35: p. 956 – I.Bernard Cohen and Anne Whitman, translators: [[Isaac Newton]], ''The Principia'': [[Mathematical Principles of Natural Philosophy]]. Preceded by ''A Guide to Newton's Principia'', by I.Bernard Cohen. University of California Press 1999 {{ISBN|0-520-08816-6}} {{ISBN|0-520-08817-4}}</ref>

:The equation for universal gravitation thus takes the form:
:<math>F=G\frac{m_1m_2}{r^2},</math>
:where ''F'' is the gravitational force acting between two objects, ''m<sub>1</sub>'' and ''m<sub>2</sub>'' are the masses of the objects, ''r'' is the distance between the [[Center of mass|centers of their masses]], and ''G'' is the [[gravitational constant]].

* '''[[Newton's laws of motion]]''' – are three [[Scientific law|law]]s of [[classical mechanics]] that describe the relationship between the [[motion]] of an object and the [[force]]s acting on it. These laws can be paraphrased as follows:<ref name="Thornton">{{cite book |last1=Thornton |first1=Stephen T. |last2=Marion |first2=Jerry B. |title=Classical Dynamics of Particles and Systems |year=2004 |publisher=Brooke Cole |isbn=0-534-40896-6 |page=49 |edition=5th}}</ref>

:''Law 1''. A body continues in its state of rest, or in uniform motion in a straight line, unless acted upon by a force.

:''Law 2''. A body acted upon by a force moves in such a manner that the time rate of change of [[momentum]] equals the force.

:''Law 3''. If two bodies exert forces on each other, these forces are equal in magnitude and opposite in direction.

:The three laws of motion were first stated by [[Isaac Newton]] in his ''[[Philosophiæ Naturalis Principia Mathematica]]'' (''Mathematical Principles of Natural Philosophy''), first published in 1687.<ref name=Principia>See the ''Principia'' on line at [https://archive.org/details/newtonspmathema00newtrich Andrew Motte Translation]</ref> Newton used them to explain and investigate the motion of many physical objects and systems, which laid the foundation for Newtonian mechanics.<ref name="Motte">{{Cite web|title=Axioms, or Laws of Motion|url=https://gravitee.tripod.com/axioms.htm|access-date=2021-02-14|website=gravitee.tripod.com}}</ref>

* '''[[Nose cone design]]''' – Given the problem of the [[aerodynamic]] [[design]] of the [[nose cone]] section of any vehicle or body meant to travel through a [[compressible fluid]] medium (such as a [[rocket]] or [[aircraft]],  [[missile]] or [[bullet]]), an important problem is the determination of the [[nose cone]] geometrical shape for optimum performance. For many applications, such a task requires the definition of a [[solid of revolution]] shape that experiences minimal resistance to rapid motion through such a fluid medium.
* '''[[Nozzle]]''' – is a device designed to control the direction or characteristics of a [[fluid]] flow (especially to increase velocity) as it exits (or enters) an enclosed chamber or [[pipe (material)|pipe]].   A nozzle is often a pipe or tube of varying cross-sectional area, and it can be used to direct or modify the flow of a fluid ([[liquid]] or [[gas]]). Nozzles are frequently used to control the rate of flow, speed, direction, mass, shape, and/or the pressure of the stream that emerges from them. In a nozzle, the velocity of fluid increases at the expense of its pressure energy.

== O ==

* '''[[Orbit]]''' – In [[physics]], an orbit is the [[gravitationally]] curved [[trajectory]] of an [[physical body|object]],<ref>[http://www.britannica.com/EBchecked/topic/431123/orbit orbit (astronomy) – Britannica Online Encyclopedia]</ref> such as the trajectory of a [[planet]] around a star or a [[natural satellite]] around a planet. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. To a close approximation, planets and satellites follow [[elliptic orbit]]s, with the [[barycenter|center of mass]] being orbited at a focal point of the ellipse,<ref>[http://spaceplace.nasa.gov/barycenter/ The Space Place :: What's a Barycenter]</ref> as described by [[Kepler's laws of planetary motion]].  For most situations, orbital motion is adequately approximated by [[Newtonian mechanics]], which explains [[Newton's law of universal gravitation|gravity]] as a force obeying an [[inverse-square law]].<ref>Kuhn, ''The Copernican Revolution'', pp. 238, 246–252</ref> However, [[Albert Einstein]]'s [[general theory of relativity]], which accounts for gravity as due to curvature of [[spacetime]], with orbits following [[geodesic]]s, provides a more accurate calculation and understanding of the exact mechanics of orbital motion.
* '''[[Orbit phasing]]''' – In astrodynamics, orbit phasing is the adjustment of the time-position of spacecraft along its orbit, usually described as adjusting the orbiting spacecraft's true anomaly.<ref>{{Cite web |url=http://ccar.colorado.edu/asen5050/projects/projects_2012/bartkowicz/website/orbital_mechanics_4.html |title=Orbital Mechanics |access-date=2013-12-13 |archive-url=https://web.archive.org/web/20131216153857/http://ccar.colorado.edu/asen5050/projects/projects_2012/bartkowicz/website/orbital_mechanics_4.html |archive-date=2013-12-16 |url-status=dead }}</ref> Orbital phasing is primarily used in scenarios where a spacecraft in a given orbit must be moved to a different location within the same orbit. The change in position within the orbit is usually defined as the phase angle, ϕ, and is the change in true anomaly required between the spacecraft's current position to the final position.
* '''[[Orbital eccentricity]]''' – In [[astrodynamics]], the orbital eccentricity of an [[astronomical object]] is a [[dimensionless quantity|dimensionless parameter]] that determines the amount by which its [[orbit]] around another body deviates from a perfect [[circle]]. A value of 0 is a [[circular orbit]], values between 0 and 1 form an [[elliptic orbit]], 1 is a [[parabola|parabolic]] [[escape orbit]], and greater than 1 is a [[hyperbola]]. The term derives its name from the parameters of [[conic section]]s, as every [[Kepler orbit]] is a conic section. It is normally used for the isolated [[two-body problem]], but extensions exist for objects following a rosette orbit through the galaxy.
* '''[[Orbital elements]]''' – are the [[parameter]]s required to uniquely identify a specific [[orbit]]. In [[celestial mechanics]] these elements are  considered in [[two-body system]]s using a [[Kepler orbit]]. There are many different ways to mathematically describe the same orbit, but certain schemes, each consisting of a set of six parameters, are commonly used in [[astronomy]] and [[orbital mechanics]].  A real orbit and its elements change over time due to gravitational [[perturbation (astronomy)|perturbations]] by other objects and the effects of [[general relativity]]. A Kepler orbit is an idealized, mathematical approximation of the orbit at a particular time.
* '''[[Orbital inclination]]''' – measures the tilt of an object's [[orbit]] around a celestial body.  It is expressed as the [[angle]] between a [[Plane of reference|reference plane]] and the [[orbital plane]] or [[Axis of rotation|axis]] of direction of the orbiting object.
* '''[[Orbital inclination change]]''' – is an [[orbital maneuver]] aimed at changing the [[inclination]] of an orbiting body's [[orbit]]. This maneuver is also known as an '''orbital plane change''' as the plane of the orbit is tipped. This maneuver requires a change in the orbital velocity vector ([[delta v]]) at the [[orbital nodes]] (i.e. the point where the initial and desired orbits intersect, the line of orbital nodes is defined by the intersection of the two orbital planes).
* '''[[Orbital maneuver]]''' – In [[spaceflight]], an orbital maneuver (otherwise known as a '''burn''') is the use of [[spacecraft propulsion|propulsion]] systems to change the [[orbit]] of a [[spacecraft]].
* '''[[Orbital mechanics]]''' – or '''astrodynamics''', is the application of [[ballistics]] and [[celestial mechanics]] to the practical problems concerning the motion of [[rocket]]s and other [[spacecraft]]. The motion of these objects is usually calculated from [[Newton's laws of motion]] and [[Newton's law of universal gravitation|law of universal gravitation]]. Orbital mechanics is a core discipline within [[space exploration|space-mission]] design and control.
* '''[[Orbital node]]''' – is either of the two points where an [[orbit]] [[intersection (Euclidean geometry)|intersects]] a [[plane of reference]] to which it is inclined.<ref name="col">{{cite encyclopedia |url=http://www.bartleby.com/65/no/node.html |title=node |encyclopedia=[[Columbia Encyclopedia]] |edition=6th |location=New York |publisher=[[Columbia University Press]] |year=2004 |access-date=May 17, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070309221338/http://www.bartleby.com/65/no/node.html |archive-date=March 9, 2007 }}</ref> A [[non-inclined orbit]], which is [[coplanarity|contained]] in the reference plane, has no nodes.
* '''[[Orbital period]]''' – (also '''revolution period'''), is the time a given [[astronomical object]] takes to complete one [[orbit]] around another object, and applies in [[astronomy]] usually to [[planet]]s or [[asteroid]]s orbiting the [[Sun]], [[moons]] orbiting planets, [[exoplanets]] orbiting other [[star]]s, or [[binary star]]s.
* '''[[Orbital station-keeping]]''' – In [[astrodynamics]], orbital station-keeping is keeping a [[spacecraft]] at a fixed distance from another spacecraft. It requires a series of [[orbital maneuver]]s made with [[Spacecraft propulsion|thruster burns]] to keep the active craft in the same orbit as its target. For many [[low Earth orbit]] satellites, the effects of [[Orbital perturbation analysis (spacecraft)|non-Keplerian]] forces, i.e. the deviations of the gravitational force of the Earth from that of a [[Shell theorem|homogeneous sphere]], gravitational forces from Sun/Moon, [[solar radiation pressure]] and air [[Drag (physics)|drag]], must be counteracted.
* '''[[Orbiter Boom Sensor System]]''' –  (OBSS), was a 50-foot (15.24 m) boom carried on board NASA's Space Shuttles. The boom was grappled by the Canadarm and served as an extension of the arm, doubling its length to a combined total of 100 feet (30 m).[1] At the far end of the boom was an instrumentation package of cameras and lasers used to scan the leading edges of the wings, the nose cap, and the crew compartment after each lift-off and before each landing. If flight engineers suspected potential damage to other areas, as evidenced in imagery captured during lift-off or the rendezvous pitch maneuver, then additional regions could be scanned.
* '''[[Osculating orbit]]''' – In [[astronomy]], and in particular in [[astrodynamics]], the osculating orbit of an object in space at a given moment in time is the gravitational [[Kepler orbit]] (i.e. an [[elliptic orbit|elliptic]] or other conic one) that it would have around its [[primary (astronomy)|central body]] if [[perturbation (astronomy)|perturbations]] were absent.<ref>{{cite book |first=Forest R. |last=Moulton |title=Introduction to Celestial Mechanics |orig-year=1902 |publisher=Dover |year=1970 |pages=322–23 |isbn=0486646874 |edition=2nd revised |location=[[Mineola, New York]]}}</ref> That is, it is the orbit that coincides with the current [[orbital state vectors]] (position and [[velocity]]).

== P ==

* '''[[Parallel axis theorem]]''' – also known as '''Huygens&ndash;Steiner theorem''', or just as '''Steiner's theorem''',<ref>{{cite book | title=Introduction to theoretical physics | author=Arthur Erich Haas | year=1928}}</ref> named after [[Christiaan Huygens]] and [[Jakob Steiner]], can be used to determine the [[moment of inertia]] or the [[second moment of area]] of a [[rigid body]] about any axis, given the body's moment of inertia about a [[Parallel (geometry)|parallel]] axis through the object's [[center of gravity]] and the [[perpendicular]] [[distance]] between the axes.
* '''[[Parasitic drag]]''' – also known as '''profile drag''',<ref name="Anderson">{{cite book |last1=Anderson |first1=John D. Jr. |title=Fundamentals of aerodynamics |date=1991 |publisher=McGraw-Hill |location=New York |isbn=0-07-001679-8 |edition=2nd}}</ref>{{rp|254}}<ref name="Anderson Introduction">{{cite book |last1=Anderson |first1=John D. Jr. |title=Introduction to flight |date=2016 |publisher=McGraw Hill Education |location=New York, NY |isbn=978-0-07-802767-3 |page=242 |edition=Eighth}}</ref>{{rp|256}} is a type of [[Drag (physics)#Aerodynamics|aerodynamic drag]] that acts on any object when the object is moving through a fluid. Parasitic drag is a combination of form drag and [[skin friction drag]].<ref>Clancy, L.J. (1975). ''Aerodynamics'', Sub-section 5.9. Pitman Publishing. {{ISBN|0 273 01120 0}}</ref><ref name="Anderson"/>{{rp|641–642}} It affects all objects regardless of whether they are capable of generating [[lift (force)|lift]].  Total drag on an aircraft is made up of parasitic drag and [[lift-induced drag]]. Parasitic drag is so named because it is not useful, whereas lift-induced drag is the result of an [[airfoil]] generating lift. Parasitic drag comprises all types of drag except lift-induced drag.<ref name="PHAK">{{cite book |title=Pilot's Handbook of Aeronautical Knowledge |publisher=FAA |page=Chapter 5, Aerodynamics of flight |url=https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/07_phak_ch5.pdf}}</ref>
* '''[[Perpendicular axes theorem]]''' – states that the [[moment of inertia]] of a [[planar lamina]] (i.e. 2-D body) about an axis perpendicular to the [[Plane (geometry)|plane]] of the lamina is equal to the sum of the moments of inertia of the lamina about the two axes at right angles to each other, in its own plane intersecting each other at the point where the perpendicular axis passes through it.

:Define perpendicular axes <math>x</math>, <math>y</math>, and <math>z</math> (which meet at origin <math>O</math>) so that the body lies in the <math>xy</math> plane, and the <math>z</math> axis is perpendicular to the plane of the body.  Let ''I''<sub>''x''</sub>, ''I''<sub>''y''</sub> and ''I''<sub>''z''</sub> be moments of inertia about axis ''x'', ''y'', ''z'' respectively. Then the perpendicular axis theorem states that<ref>{{cite book |title=Physics |author=Paul A. Tipler |chapter=Ch. 12: Rotation of a Rigid Body about a Fixed Axis |publisher=Worth Publishers Inc. |isbn=0-87901-041-X |year=1976 |url-access=registration |url=https://archive.org/details/physics00tipl }}</ref>

::<math>I_z = I_x + I_y</math>

:This rule can be applied with the [[parallel axis theorem]] and the [[stretch rule]] to find polar moments of inertia for a variety of shapes.

:If a planar object (or prism, by the [[stretch rule]]) has rotational symmetry such that <math>I_x</math> and <math>I_y</math> are equal,<ref>{{cite book
|first= Joaquin
|last= Obregon
|title= Mechanical Simmetry
|isbn = 978-1-4772-3372-6
|year= 2012
|publisher= AuthorHouse
|url = https://www.researchgate.net/publication/273061569
}}</ref>
:then the perpendicular axes theorem provides the useful relationship:

::<math>I_z = 2I_x = 2I_y</math>
* '''Pitch Angle''' – 
* '''[[Plasma (physics)]]''' – ({{ety|grc|πλάσμα|moldable substance}})<ref name="πλάσμα">[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dpla%2Fsma πλάσμα] {{webarchive|url=https://web.archive.org/web/20130618012819/http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dpla%2Fsma |date=18 June 2013 }}, Henry George Liddell, Robert Scott, ''A Greek English Lexicon'', on Perseus</ref> is one of the [[State of matter#Four fundamental states|four fundamental states of matter]]. It consists of a gas of [[ion]]s{{Snd}}atoms or molecules which have at least one orbital [[electron]] stripped (or an extra electron attached) and, thus, an electric charge.  It is the most abundant form of [[Baryon#Baryonic matter|ordinary matter]] in the [[universe]],<ref name="Itptma2013a">{{cite book
|last1=Chu

|first1=P.K.|last2=Lu
|first2=XinPel
|date=2013
|title=Low Temperature Plasma Technology: Methods and Applications
| page=3
|publisher=CRC Press
|isbn=978-1-4665-0990-0}}</ref> being mostly associated with [[star]]s,<ref name="Piel2010">{{Cite book
|last =Piel
|first=A.
|date=2010
|title= Plasma Physics: An Introduction to Laboratory, Space, and Fusion Plasmas
|pages= 4–5
|publisher=[[Springer Nature|Springer]]
|url=https://books.google.com/books?id=9cA0DwAAQBAJ&pg=PR8
|isbn=978-3-642-10491-6
|url-status=live
|archive-url=https://web.archive.org/web/20160105142523/https://books.google.com/books?hl=en
|archive-date=5 January 2016
 |df = dmy-all
}}</ref> including the [[Sun]].<ref name="Phillips1995">
{{Cite book
|last=Phillips
|first=K. J. H.
|date=1995
|title=Guide to the Sun
|page=295
|publisher=[[Cambridge University Press]]
|url=https://books.google.com/books?id=idwBChjVP0gC&q=Guide+to+the+Sun+phillips
|isbn=978-0-521-39788-9
|url-status=live
|archive-url= https://web.archive.org/web/20180115215631/https://books.google.com/books?id=idwBChjVP0gC&printsec=frontcover&dq=Guide+to+the+Sun+phillips&hl=en&sa=X&ved=0ahUKEwiBj4Gbj5bXAhXrrVQKHfnAAKUQ6AEIKDAA
|archive-date=15 January 2018
|df=dmy-all}}</ref><ref name="Aschwanden2004">{{cite book
|last=Aschwanden
|first=M. J.
|year=2004
|title=Physics of the Solar Corona. An Introduction
|publisher=Praxis Publishing
|isbn=978-3-540-22321-4}}</ref>  It extends to the rarefied [[intracluster medium]] and possibly to [[Outer space#Intergalactic space|intergalactic regions]].<ref name="BoPA2015">{{cite book
|last1=Chiuderi
|first1=C.
|last2=Velli
|first2=M.
|date=2015
|title=Basics of Plasma Astrophysics
|page=17
|publisher=[[Springer Nature|Springer]]
|isbn=978-88-470-5280-2}}</ref>
* '''[[Plug nozzle]]''' – is a type of [[nozzle]] which includes a centerbody or plug around which the working fluid flows.  Plug nozzles have applications in aircraft, rockets, and numerous other fluid flow devices.
* '''[[Pogo oscillation]]''' – 
* '''[[Prandtl–Glauert singularity]]''' – 
* '''[[Precession]]''' – 
* '''[[Pressure]]''' – 
* '''[[Pressure altitude]]''' – 
* '''[[Pressure-fed engine (rocket)|Pressure-fed engine]]''' – 
* '''[[Propeller (aircraft)|Propeller]]''' – 
* '''[[Proper orbital elements]]''' – 
* '''[[Pulsed inductive thruster]]''' – 
* '''[[Pulsed plasma thruster]]''' – 
* '''[[Propulsion]]''' –

== Q ==

{{Empty section|date=March 2022}}

== R ==

* '''[[Radar]]''' – system using the reflection from transmitted [[electromagnetic wave]]s to detect the distance and rough shape of an object, working even in [[outer space]], unlike [[sonar]]
* '''[[Radio direction finder]]''' – 
* '''[[Railgun]]''' – 
* '''[[Ram accelerator]]''' – 
* '''[[Ramjet]]''' – 
* '''[[Rate of climb]]''' –
* '''RCS ([[Reaction control system]])''' – set of [[Spacecraft propulsion|rocket thrusters]] used for [[spacecraft]] maneuvers over the craft's three [[Aircraft principal axes|rotation axes]] in [[outer space]]
* '''[[Atmospheric reentry|Reentry]]''' – 
* '''[[Reflection (physics)|Reflection]]''' – 
* '''[[Relativistic rocket]]''' – 
* '''[[Remote Manipulator System]]''' – 
* '''[[Resistojet rocket]]''' – 
* '''[[Reusable launch system]]''' – 
* '''[[Reynolds number]]''' – 
* '''[[RL-10 (rocket engine)]]''' – 
* '''[[Rocket]]''' – 
* '''[[Rocket engine]]''' –
* '''[[Rocket engine nozzle]]''' – 
* '''[[Rocket fuel]]''' – 
* '''[[Rocket launch]]''' – 
* '''[[Rogallo wing]]''' – is a flexible type of [[wing]]. In 1948, [[Francis Rogallo]], a [[NASA]] engineer, and his wife [[Gertrude Rogallo]], invented a self-inflating flexible wing they called the '''Parawing''', also known after them as the "Rogallo Wing" and '''flexible wing'''.<ref>{{cite web|url=https://history.nasa.gov/SP-4308/ch11.htm#382 |title=Rogallo Wing -the story told by NASA |publisher=History.nasa.gov |access-date=2012-12-23}}</ref> NASA considered Rogallo's flexible wing as an alternative recovery system for the [[Project Mercury|Mercury]] and [[Project Gemini|Gemini]] [[space capsule]]s, and for possible use in other spacecraft landings, but the idea was dropped from Gemini in 1964 in favor of [[parachute#Round|conventional parachute]]s.
* '''[[Rudder]]''' –

== S ==

* '''[[Reaction Engines SABRE|SABRE]]''' – 
* '''[[Satellite]]''' – 
* '''[[Saturn (rocket family)]]''' – 
* '''[[Scalar (physics)]]''' – A quantity with magnitude but no direction.
* '''[[Schlieren]]''' – 
* '''[[Schlieren photography]]''' – 
* '''[[Scramjet]]''' – 
* '''[[Second moment of area]]''' – 
* '''[[Shock wave]]''' – 
* '''[[SI]]''' – 
* '''[[Single point of failure]]''' – 
* '''[[Single-stage-to-orbit]]''' – [[spacecraft]] able to fly from a [[celestial body]] (usually the [[Earth]] or the [[Moon]])'s surface to its orbit without using external boosters
* '''[[Skyhook (structure)]]''' – 
* '''[[Slew (spacecraft)|Slew]]''' – 
* '''[[Stream function]]''' – 
* '''[[Streamlines, streaklines, and pathlines|Streamline]]''' – 
* '''[[Photovoltaic module|Solar panel]]''' – 
* '''[[Solar sail]]''' – 
* '''[[Solar thermal rocket]]''' – 
* '''[[Solid of revolution]]''' – 
* '''[[Solid rocket]]''' – 
* '''[[Sound barrier]]''' – 
* '''[[Space activity suit]]''' – 
* '''[[Space elevator]]''' – 
* '''[[Space fountain]]''' – 
* '''[[Space Shuttle program|Space Shuttle]]''' – crewed [[NASA]] [[spacecraft]] used between 1981 and 2011, consisting of a reusable [[spaceplane]] (the [[Space Shuttle orbiter]], capable of [[airplane]]-like landing) attached to an expendable [[Space Shuttle external tank|external tank]] (which disintegrated during [[Atmospheric entry|re-entry]]) and two recoverable [[solid rocket boosters]] (which re-entered the [[Earth]]'s atmosphere and splash-landed)
* '''[[Space Shuttle external tank]]''' – external tank attached to the [[Space Shuttle orbiter|orbiter]] and the [[solid rocket boosters]] in the [[NASA]] [[Space Shuttle program]]
* '''[[Space Shuttle main engine]]''' – 
* '''[[Space Shuttle orbiter]]''' – reusable [[NASA]] [[Vertical, takeoff, horizontal landing|VTHL]] [[spaceplane]] used during the [[Space Shuttle program]] (1981–2011)
* '''[[Space station]]''' – habitable [[artificial satellite]]
* '''[[Space suit]]''' – 
* '''[[Space technology]]''' – 
* '''[[Space transport]]''' – 
* '''[[Spacecraft]]''' – 
* '''[[Spacecraft design]]''' – 
* '''[[Spacecraft propulsion]]''' – 
* '''[[Spaceplane]]''' – vehicle capable of both atmospheric flight according to the laws of [[aerodynamics]] (like an [[aircraft]]) and [[spaceflight]] in [[outer space]] (like a [[spacecraft]])
* '''[[Special relativity]]''' – 
* '''[[Specific impulse]]''' – 
* '''[[Speed of sound]]''' – 
* '''SRB''' – [[solid rocket booster]]
* '''SSTO''' – [[single-stage-to-orbit]]
* '''[[Staged combustion cycle (rocket)]]''' – 
* '''[[Hypersonic speed#Classification of Mach regimes|Subsonic]]''' – inferior to the [[speed of sound]]
* '''[[Hypersonic speed#Classification of Mach regimes|Supersonic]]''' – superior to the [[speed of sound]]
* '''[[Surface of revolution]]''' – 
* '''[[Sweep theory]]''' –

== T ==

* '''[[Tait–Bryan rotations]]''' – 
* '''[[Temperature]]''' – 
* '''[[Terminal velocity]]''' – is the maximum velocity (speed) attainable by an object as it falls through a [[fluid]] ([[air]] is the most common example). It occurs when the sum of the [[Drag (physics)|drag]] force (''F<sub>d</sub>'') and the [[buoyancy]] is equal to the downward force of [[gravity]] (''F<sub>G</sub>'') acting on the object. Since the [[net force]] on the object is zero, the object has zero [[acceleration]].<ref>{{cite web
| publisher = NASA Glenn Research Center
| title = Terminal Velocity
| url = http://www.grc.nasa.gov/WWW/K-12/airplane/termv.html
| access-date = March 4, 2009
| archive-date = February 23, 2009
| archive-url = https://web.archive.org/web/20090223132724/http://www.grc.nasa.gov/WWW/K-12/airplane/termv.html
| url-status = dead
}}</ref>
* '''[[Test target]]''' – 
* '''[[Tether propulsion]]''' – 
* '''[[Space Shuttle thermal protection system|Thermal protection system]]''' – 
* '''[[Thermodynamics]]''' – 
* '''[[Thrust]]''' – 
* '''[[Thruster (disambiguation)|Thruster]]''' – 
* '''[[Torricelli's equation]]''' –   In physics, Torricelli's equation, or Torricelli's formula, is an equation created by [[Evangelista Torricelli]] to find the final [[velocity]] of an object moving with a [[Acceleration#Uniform acceleration|constant acceleration]] along an axis (for example, the x axis) without having a known time interval.

:::The equation itself is:<ref name="Bertoldo2008">{{cite book|author=Leandro Bertoldo|title=Fundamentos do Dinamismo|url=https://books.google.com/books?id=cX1JBQAAQBAJ&pg=PA41|date=2008|location=[[Joinville]]|publisher=[[Clube de Autores]]|pages=41–42|language=Portuguese}}</ref>

:::<math> v_f^2 = v_i^2 + 2a\Delta x \,</math>

:::where
:::*<math>v_f</math> is the object's final [[velocity]] along the x axis on which the acceleration is constant.
:::*<math>v_i</math> is the object's initial velocity along the x axis.
:::*<math>a</math> is the object's [[acceleration]] along the x axis, which is given as a constant.
:::*<math>\Delta x \,</math> is the object's change in position along the x axis, also called [[Displacement (vector)|displacement]].

:::This equation is valid along any axis on which the acceleration is constant.
* '''[[Total air temperature]]''' – In aviation, [[stagnation temperature]] is known as total air temperature and is measured by a [[temperature probe]] mounted on the surface of the aircraft. The probe is designed to bring the air to rest relative to the aircraft. As the air is brought to rest, [[kinetic energy]] is converted to [[internal energy]]. The air is compressed and experiences an [[adiabatic process|adiabatic]] increase in temperature. Therefore, total [[air temperature]] is higher than the static (or ambient) air temperature.  Total air temperature is an essential input to an [[air data computer]] in order to enable the computation of static air temperature and hence [[true airspeed]].
* '''[[Trajectory]]''' – or flight path, is the path that an [[physical body|object]] with [[mass]] in [[Motion (physics)|motion]] follows through [[space]] as a function of time. In [[classical mechanics]], a trajectory is defined by [[Hamiltonian mechanics]] via [[canonical coordinates]]; hence, a complete trajectory is defined by position and [[momentum]], simultaneously.  The mass might be a [[projectile]] or a [[satellite]].<ref>{{cite book |title=The Principles of Physics |first=Rohit |last=Metha |chapter=11 |page=378}}</ref> For example, it can be an [[orbit]] — the path of a [[planet]], [[asteroid]], or [[comet]] as it travels around a [[primary (astronomy)|central mass]].
* '''[[Trailing edge]]''' – 
* '''[[Trans Lunar Injection]]''' – 
* '''[[Transonic]]''' – 
* '''[[Transverse wave]]''' – 
* '''[[Tripropellant rocket]]''' – 
* '''[[Tsiolkovsky rocket equation]]''' – 
* '''[[Turbomachinery]]''' – 
* '''[[Two-stage-to-orbit]]''' –

== U ==

* '''[[UFO]]''' – An unidentified flying object is any perceived aerial phenomenon that cannot be immediately identified or explained. On investigation, most UFOs are [[Identification studies of UFOs|identified]] as known objects or atmospheric phenomena, while a small number remain unexplained.

== V ==

* '''[[V-2 rocket]]''' – The '''V-2''' ({{langx|de|[[V-weapons|Vergeltungswaffe]] 2}}, "Retribution Weapon 2"), with the technical name ''[[Aggregat (rocket family)|Aggregat]] 4'' ('''A4'''), was the world's first long-range<ref>[http://www-pao.ksc.nasa.gov/history/rocket-history.htm "Long-range" in the context of the time. See NASA history article] {{webarchive |url=https://web.archive.org/web/20090107190509/http://www-pao.ksc.nasa.gov/history/rocket-history.htm |date=7 January 2009}}</ref> [[missile guidance|guided]] [[ballistic missile]]. The missile, powered by a [[liquid-propellant rocket]] engine, was developed during the [[Second World War]] in [[Nazi Germany|Germany]] as a "[[V-weapons|vengeance weapon]]" and assigned to attack Allied cities as retaliation for the [[Strategic bombing during World War II#The British later in the war|Allied bombings]] against German cities. The {{nowrap|V-2}} rocket also became the first artificial object to travel into space by crossing the [[Kármán line]] with the vertical launch of [[MW 18014]] on 20 June 1944.<ref>{{cite book |title=The Rocket and the Reich: Peenemünde and the Coming of the Ballistic Missile Era |url=https://archive.org/details/isbn_9780029228951 |url-access=registration |last=Neufeld |first=Michael J. |publisher=The Free Press |year=1995 |location=New York |pages=[https://archive.org/details/isbn_9780029228951/page/158 158], 160–162, 190 |isbn=9780029228951 |access-date=15 November 2019 |archive-url=https://web.archive.org/web/20191028112702/https://archive.org/details/isbn_9780029228951 |archive-date=28 October 2019 |url-status=live }}</ref>
* '''[[Variable specific impulse magnetoplasma rocket]]''' – (VASIMR), is an electrothermal thruster under development for possible use in [[spacecraft propulsion]]. It uses [[radio wave]]s to [[ionization|ionize]] and heat an [[chemically inert|inert]] [[rocket propellant|propellant]], forming a plasma, then a [[magnetic field]] to confine and accelerate the expanding [[Plasma (physics)|plasma]], generating [[thrust]]. It is a [[plasma propulsion engine]], one of several types of spacecraft [[Electrically powered spacecraft propulsion|electric propulsion]] systems.<ref name="VASIMR-Engine">{{cite web |url=http://www.adastrarocket.com/aarc/VASIMR |title=VASIMR |author=Ad Astra Rocket Company |publisher=Ad Astra Rocket Company |access-date=July 9, 2019 |archive-url=https://web.archive.org/web/20190707234837/http://www.adastrarocket.com/aarc/VASIMR |archive-date=July 7, 2019 |url-status=dead }}</ref>
* '''[[Velocity]]''' – The velocity of an object is the [[Time derivative|rate of change]] of its [[Position (vector)|position]] with respect to a [[frame of reference]], and is a function of time. Velocity is equivalent to a specification of an object's [[speed]] and direction of [[motion (physics)|motion]] (e.g. {{val|60|u=[[Kilometres per hour|km/h]]}} to the north). Velocity is a fundamental concept in [[kinematics]], the branch of [[classical mechanics]] that describes the motion of bodies.

:Velocity is a physical [[vector (geometry)|vector]] [[Physical quantity|quantity]]; both magnitude and direction are needed to define it. The [[Scalar (physics)|scalar]] [[absolute value]] ([[Magnitude (mathematics)|magnitude]]) of velocity is called {{em|speed}}, being a coherent derived unit whose quantity is measured in the [[International System of Units|SI]] ([[metric system]]) as [[metres per second]] (m/s or m⋅s<sup>−1</sup>). For example, "5 metres per second" is a scalar, whereas "5 metres per second east" is a vector. If there is a change in speed, direction or both, then the object is said to be undergoing an ''[[acceleration]]''.
* '''[[Viscometer]]''' – (also called '''viscosimeter''') is an instrument used to measure the [[viscosity]] of a [[fluid]]. For liquids with viscosities which vary with [[flow conditioning|flow conditions]], an instrument called a [[rheometer]] is used. Thus, a rheometer can be considered as a special type of viscometer.<ref>{{cite book |last1=Barnes |first1=H. A. |last2=Hutton |first2=J. F. |last3=Walters |first3=K. |title=An introduction to rheology |date=1989 |publisher=Elsevier |location=Amsterdam |isbn=978-0-444-87140-4 |page=12 |edition=5. impr.}}</ref> Viscometers only measure under one flow condition.
* '''[[Viscosity]]''' – The viscosity of a [[fluid]] is a measure of its [[drag (physics)|resistance]] to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, [[syrup]] has a higher viscosity than [[water]].<ref>{{cite book|last=Symon|first=Keith R.|title=Mechanics|url=https://books.google.com/books?id=JVk_4udwNtkC|edition=3rd|year=1971|publisher=Addison-Wesley|isbn=978-0-201-07392-8|access-date=2019-09-18|archive-date=2020-03-11|archive-url=https://web.archive.org/web/20200311030312/https://books.google.com/books?id=JVk_4udwNtkC|url-status=live}}</ref>
* '''[[Vortex generator]]''' – (VG), is an [[aerodynamic]] device, consisting of a small [[wikt:vane|vane]] usually attached to a lifting surface (or [[airfoil]], such as an [[aircraft|aircraft wing]])<ref name="Peppler"/> or a rotor blade of a [[wind turbine]].<ref name="WindTurbineVortexGenerators">[http://www.upwindsolutions.com/upgrades/wind-turbine-vortex-generator/ Wind Turbine Vortex Generators] {{Webarchive|url=https://web.archive.org/web/20150323062821/http://www.upwindsolutions.com/upgrades/wind-turbine-vortex-generator/ |date=2015-03-23 }}, UpWind Solutions.</ref> VGs may also be attached to some part of an aerodynamic vehicle such as an aircraft fuselage or a car.  When the airfoil or the body is in motion relative to the air, the VG creates a [[vortex]],<ref name="Peppler">Peppler, I.L.: ''From The Ground Up'', page 23. Aviation Publishers Co. Limited, Ottawa Ontario, Twenty Seventh Revised Edition, 1996. {{ISBN|0-9690054-9-0}}</ref><ref name="MicroHow">{{cite web|url = http://www.microaero.com/pages/v_howvgswrk.html|title = How Micro VGs Work|access-date = 2008-03-15|last = Micro AeroDynamics|year = 2003}}</ref>  which, by removing some part of the slow-moving boundary layer in contact with the airfoil surface, delays local [[flow separation]] and [[Stall (fluid dynamics)|aerodynamic stalling]], thereby improving the effectiveness of wings and [[Wing configuration#Tailplanes and foreplanes|control surfaces]], such as [[Flap (aeronautics)|flaps]], [[Elevator (aeronautics)|elevators]], [[aileron]]s, and [[rudder]]s.<ref name="MicroHow"/>

== W ==

* '''[[Wave drag]]''' – In [[aeronautics]], wave drag is a component of the [[aerodynamic drag]] on aircraft wings and fuselage, propeller blade tips and [[Shell (projectile)|projectiles]] moving at [[transonic]] and [[supersonic]] speeds, due to the presence of [[shock wave]]s.<ref>{{cite book |last1=Anderson |first1=John D. Jr. |title=Fundamentals of aerodynamics |date=1991 |publisher=McGraw-Hill |location=New York |isbn=0-07-001679-8 |pages=492, 573 |edition=2nd}}</ref> Wave drag is independent of [[viscous effect]]s,<ref name=LJC11.7>Clancy, L.J. (1975), ''Aerodynamics'', Section 11.7</ref> and tends to present itself as a sudden and dramatic increase in drag as the vehicle increases speed to the [[Critical Mach number]]. It is the sudden and dramatic rise of wave drag that leads to the concept of a [[sound barrier]].
* '''[[Weight]]''' – In [[science]] and [[engineering]], the '''weight''' of an object is the [[force]] acting on the object due to [[gravity]].<ref name="Morrison">{{cite journal
|title=Weight and gravity - the need for consistent definitions
|author=Richard C. Morrison
|journal=[[The Physics Teacher]]
|volume=37 |page=51 |date=1999 |issue=1
|doi=10.1119/1.880152
|bibcode = 1999PhTea..37...51M }}</ref><ref name="Galili">{{cite journal
|title=Weight versus gravitational force: historical and educational perspectives
|author=Igal Galili
|journal=International Journal of Science Education
|volume=23 |page=1073 |date=2001 |issue=10
|doi=10.1080/09500690110038585
|bibcode = 2001IJSEd..23.1073G |s2cid=11110675
}}</ref><ref name="Gat">{{cite book |title=Standardization of Technical Terminology: Principles and Practice – ''second volume'' |editor=Richard Alan Strehlow |date=1988 |publisher=[[ASTM International]] |isbn=978-0-8031-1183-7 |chapter=The weight of mass and the mess of weight |last=Gat |first=Uri |pages=45–48 |chapter-url=https://books.google.com/books?id=CoB5w9Km0mUC&pg=PA45}}</ref>
* '''[[Weight function]]''' –  is a mathematical device used when performing a sum, integral, or average to give some elements more "weight" or influence on the result than other elements in the same set. The result of this application of a weight function is a '''weighted sum''' or [[weighted average]]. Weight functions occur frequently in [[statistics]] and [[mathematical analysis|analysis]], and are closely related to the concept of a [[measure (mathematics)|measure]].  Weight functions can be employed in both discrete and continuous settings. They can be used to construct systems of calculus called "weighted calculus"<ref>Jane Grossman, Michael Grossman, Robert Katz. [https://books.google.com/books?as_brr=0&q=%22The+First+Systems+of+Weighted+Differential+and+Integral+Calculus%E2%80%8E%22&btnG=Search+Books, ''The First Systems of Weighted Differential and Integral Calculus''], {{isbn|0-9771170-1-4}}, 1980.</ref> and "meta-calculus".<ref>Jane Grossman.[https://books.google.com/books?q=%22Non-Newtonian+Calculus%22&btnG=Search+Books&as_brr=0, ''Meta-Calculus: Differential and Integral''], {{isbn|0-9771170-2-2}}, 1981.</ref>
* '''[[Wind tunnel]]s''' –  are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft will fly. [[NASA]] uses wind tunnels to test [[scale model]]s of aircraft and spacecraft. Some wind tunnels are large enough to contain full-size versions of vehicles. The wind tunnel moves air around an object, making it seem as if the object is flying.
* '''[[Wing]]''' – is a type of [[fin]] that produces [[Lift (force)|lift]] while moving through air or some other [[fluid]]. Accordingly, wings have [[Streamlines, streaklines, and pathlines|streamlined]] [[Cross section (geometry)|cross-sections]] that are subject to [[aerodynamic force]]s and act as [[airfoil]]s. A wing's [[Aerodynamics|aerodynamic]] efficiency is expressed as its [[lift-to-drag ratio]]. The lift a wing generates at a given speed and [[angle of attack]] can be one to two [[order of magnitude|orders of magnitude]] greater than the total [[drag (physics)|drag]] on the wing. A high lift-to-drag ratio requires a significantly smaller [[thrust]] to propel the wings through the air at sufficient lift.
* '''[[Wright Flyer]]''' – The '''''Wright Flyer''''' (the '''''Kitty Hawk''''',<ref>[https://airandspace.si.edu/collection-objects/1903-wright-flyer/nasm_A19610048000 Smithsonian Air and Space museum collection (click on Long Description)]</ref><ref>[[:File:Wright flyer fragments STS-51-L.jpg|Orville Wright note]]</ref> also known as '''''Flyer'' I''' or '''1903 ''Flyer''''') made the first sustained flight by a manned [[heavier-than-air]] powered and controlled aircraft—an [[airplane]]—on 17 December 1903.<ref name=NASM>{{cite web |title=Wright Brothers |url=https://airandspace.si.edu/learn/highlighted-topics/wright-brothers |website=Smithsonian National Air and Space Museum |access-date=29 September 2021 |archive-date=29 September 2021 |archive-url=https://web.archive.org/web/20210929043536/https://airandspace.si.edu/learn/highlighted-topics/wright-brothers |url-status=dead }}</ref> Invented and flown by [[Wright brothers|Orville and Wilbur Wright]], it marked the beginning of the [[Aviation in the pioneer era|"pioneer era"]] of aviation.
* '''[[Wright Glider]]''' – The [[Wright brothers]] designed, built and flew a series of three manned [[Glider (aircraft)|gliders]] in 1900–1902 as they worked towards achieving powered [[flight]]. They also made preliminary tests with a [[kite]] in 1899. In 1911 Orville conducted tests with a much more sophisticated glider. Neither the kite nor any of the gliders were preserved, but replicas of all have been built.

== X ==

{{Empty section|date=March 2022}}

== Y ==

{{Empty section|date=March 2022}}

== Z ==

{{Empty section|date=March 2022}}

== See also ==

* [[Aerospace engineering]]
* [[List of aviation, aerospace and aeronautical abbreviations]]
* [[Engineering]]
* [[Glossary of engineering]]
* [[National Council of Examiners for Engineering and Surveying]] (NCEES)
* [[Fundamentals of Engineering Examination]]
* [[Principles and Practice of Engineering Examination]] (PE exam)
* [[Graduate Aptitude Test in Engineering]] (GATE)
* [[Glossary of areas of mathematics]]
* [[Glossary of artificial intelligence]]
* [[Glossary of astronomy]]
* [[Glossary of biology]]
* [[Glossary of chemistry terms|Glossary of chemistry]]
* [[Glossary of civil engineering]]
* [[Glossary of economics]]
* [[Glossary of mechanical engineering]]
* [[Glossary of physics]]
* [[Glossary of probability and statistics]]
* [[Glossary of structural engineering]]

== References ==

{{Reflist}}
{{reflist|group=lower-alpha}}
{{reflist|group=note}}

{{Engineering fields}}

{{Glossaries of science and engineering}}

[[Category:Aerospace engineering|*]]
[[Category:Engineering disciplines]]
[[Category:Glossaries of science|aerospace engineering]]
[[Category:Indexes of engineering topics|Aerospace engineering topics]]
[[Category:Glossaries of technology|Aerospace engineering]]
[[Category:Wikipedia glossaries using unordered lists]]