View source for Sub-orbital spaceflight

{{short description|Spaceflight where the spacecraft does not go into orbit}}
[[File:Riding on a Sounding Rocket.webm|thumb|Video of sub-orbital spaceflight of [[Black Brant IX]] sounding rocket]]
{| class="wikitable floatright" style="text-align:center;"
|+ Sub-orbital human spaceflight ([[Fédération Aéronautique Internationale|FAI]]-defined [[space border]])
|-
! Name !! Year !! Flights  !! Location
|-
| [[Mercury-Redstone 3]] <br /> [[Mercury-Redstone 4]] || 1961 || 2 || [[Cape Canaveral]]
|-
| [[X-15 Flight 90]] <br /> [[X-15 Flight 91]] || 1963 || 2 || [[Edwards AFB]]
|-
| [[Soyuz 18a]] || 1975 || 1 || [[Baikonur Cosmodrome]]
|-
| [[SpaceShipOne flight 15P|SpaceShipOne Flight 15P]]<br /> [[SpaceShipOne flight 16P|SpaceShipOne Flight 16P]]<br /> [[SpaceShipOne flight 17P|SpaceShipOne Flight 17P]] || 2004 || 3 || [[Mojave Air and Space Port]]
|-
| [[Blue Origin NS-16]]<ref name=sn20210720>{{cite news |url=https://spacenews.com/blue-origin-launches-bezos-on-first-crewed-new-shepard-flight/ |title=Blue Origin launches Bezos on first crewed New Shepard flight |last=Foust|first=Jeff |work=[[SpaceNews]] |date=20 July 2021 |access-date=20 Jul 2021 }}</ref><br /> [[Blue Origin NS-18]]<br /> [[Blue Origin NS-19]] || 2021 || 3 || rowspan="3" | [[Corn Ranch]]
|-
| [[Blue Origin NS-20]]<br /> [[Blue Origin NS-21]]
[[Blue Origin NS-22]]
| 2022 || 3
|-
|[[Blue Origin NS-25]]<br /> [[Blue Origin NS-26]]
|2024
|2
|}

{| class="wikitable floatright" style="text-align:center;"
|+ Sub-orbital human spaceflight (United States-defined [[space border]]; excluding those above)
|-
! Name !! Year !! Flights  !! Location
|-
| [[X-15 Flight 62]] || 1962 || 1 ||rowspan="6" | [[Edwards AFB]]
|-
| [[North American X-15#Highest flights|X-15 Flight 77]] <br /> [[X-15 Flight 87]] || 1963 || 2
|-
| [[North American X-15#Highest flights|X-15 Flight 138]] <br /> [[North American X-15#Highest flights|X-15 Flight 143]] <br /> [[North American X-15#Highest flights|X-15 Flight 150]] <br /> [[North American X-15#Highest flights|X-15 Flight 153]] || 1965 || 4
|-
| [[North American X-15#Highest flights|X-15 Flight 174]] || 1966 || 1
|-
| [[North American X-15#Highest flights|X-15 Flight 190]] <br /> [[X-15 Flight 3-65-97|X-15 Flight 191]] || 1967 || 2
|-
| [[North American X-15#Highest flights|X-15 Flight 197]] || 1968 || 1
|-
| [[Soyuz MS-10]] || 2018 || 1 || [[Baikonur Cosmodrome]]
|-
| [[VSS Unity VP-03|VSS ''Unity'' VP-03]] || 2018 || 1 ||rowspan="2" | [[Mojave Air and Space Port]]
|-
| [[VSS Unity VF-01|VSS ''Unity'' VF-01]] || 2019 || 1
|-
|[[VSS Unity Unity21|VSS ''Unity'' Unity21]]<br />[[Virgin Galactic Unity 22|VSS ''Unity'' Unity22]]
|2021
|2
|[[Spaceport America]]
|-
|[[Virgin Galactic Unity 25|VSS ''Unity'' Unity25]]<br />[[Galactic 01]]<br />[[Galactic 02]]<br />[[Galactic 03]]<br />[[Galactic 04]]<br />[[Galactic 05]]
|2023
|6
|[[Spaceport America]]
|-
|[[Galactic 06]]<br />[[Galactic 07]]
|2024
|2
|[[Spaceport America]]
|}

A '''sub-orbital spaceflight''' is a [[spaceflight]] in which the [[spacecraft]] reaches [[outer space]], but its [[trajectory]] intersects the surface of the [[primary (astronomy)|gravitating body]] from which it was launched. Hence, it will not complete one [[orbit]]al revolution, will not become an [[artificial satellite]] nor will it reach [[escape velocity]].

For example, the path of an object launched from [[Earth]] that reaches the [[Kármán line]] (about {{cvt|83|km|mi|0|disp=sqbr}} – {{cvt|100|km|mi|0|disp=sqbr}}<ref>{{Cite journal | url=https://scholar.smu.edu/cgi/viewcontent.cgi?article=1126&context=jalc | title=The Vertical Limit of State Sovereignty | journal=Journal of Air Law and Commerce | volume=72 | issue=1 | first=Dean N. | last=Reinhardt | year=2007 }}</ref> above [[sea level]]), and then falls back to Earth, is considered a sub-orbital spaceflight. Some sub-orbital flights have been undertaken to test spacecraft and [[launch vehicle]]s later intended for [[orbital spaceflight]]. Other vehicles are specifically designed only for sub-orbital flight; examples include crewed vehicles, such as the [[North American X-15|X-15]] and [[SpaceShipTwo]], and uncrewed ones, such as [[intercontinental ballistic missile|ICBMs]] and [[sounding rocket]]s.

Flights which attain sufficient velocity to go into [[low Earth orbit]], and then [[de-orbit]] before completing their first full orbit, are not considered sub-orbital. Examples of this include flights of the [[Fractional Orbital Bombardment System]].

A flight that does not reach space is still sometimes called sub-orbital, but cannot officially be classified as a "sub-orbital spaceflight". Usually a rocket is used, but some experimental sub-orbital spaceflights have also been achieved via the use of [[space gun]]s.<ref>{{cite web |url=http://www.astronautix.com/fam/martlet.htm |title=Martlet |url-status=dead |archive-url=https://web.archive.org/web/20100926022558/http://www.astronautix.com/fam/martlet.htm |archive-date=2010-09-26}}</ref>

==Altitude requirement==
[[Image:Newton Cannon.svg|thumb|right|[[Newton's cannonball|Isaac Newton's Cannonball]]. Paths A and B depict a sub-orbital trajectory.]]
By definition, a sub-orbital spaceflight reaches an [[altitude]] higher than {{convert|100|km|abbr=on}} above [[sea level]]. This altitude, known as the Kármán line, was chosen by the [[Fédération Aéronautique Internationale]] because it is roughly the point where a vehicle flying fast enough to support itself with [[aerodynamic lift]] from the [[Earth's atmosphere]] would be flying faster than [[orbital speed]].<ref>{{cite web|url=http://www.fai.org/icare-records/100km-altitude-boundary-for-astronautics|title=100 km Altitude Boundary for Astronautics|publisher=[[Fédération Aéronautique Internationale]]|archive-url=https://web.archive.org/web/20110809093537/http://www.fai.org/astronautics/100km.asp|archive-date=2011-08-09|url-status=dead|access-date=2017-09-14}}</ref> The US military and [[NASA]] award [[Astronaut Badge|astronaut wings]] to those flying above {{convert|50|mi|abbr=on}},<ref>{{cite web|url=http://www.nasa.gov/centers/dryden/news/NewsReleases/2005/05-57.html|title=X-15 Space Pioneers Now Honored as Astronauts|first=Mary|last=Whelan|date=5 June 2013|website=nasa.gov|access-date=4 May 2018|url-status=live|archive-url=https://web.archive.org/web/20170611194526/https://www.nasa.gov/centers/dryden/news/NewsReleases/2005/05-57.html|archive-date=11 June 2017}}</ref> although the [[U.S. State Department]] does not show a distinct boundary between atmospheric flight and [[spaceflight]].<ref>{{cite web|url=https://2009-2017.state.gov/s/l/22718.htm|title=85. U.S. Statement, Definition and Delimitation of Outer Space And The Character And Utilization Of The Geostationary Orbit, Legal Subcommittee of the United Nations Committee on the Peaceful Uses of Outer Space at its 40th Session in Vienna from April|website=state.gov|access-date=4 May 2018}}</ref>

==Orbit==
During [[freefall]] the trajectory is part of an [[elliptic orbit]] as given by the [[orbit equation]]. The [[perigee]] distance is less than the [[radius of the Earth]] ''R'' including atmosphere, hence the [[ellipse]] intersects the Earth, and hence the spacecraft will fail to complete an orbit. The major axis is vertical, the [[semi-major axis]] ''a'' is more than ''R''/2. The [[specific orbital energy]] <math>\epsilon</math> is given by:

<math display="block">\varepsilon = -{\mu \over {2a}} > -{\mu \over {R}}\,\!</math>

where <math>\mu\,\!</math> is the [[standard gravitational parameter]].

Almost always ''a'' < ''R'', corresponding to a lower <math>\epsilon</math> than the minimum for a full orbit, which is <math>-{\mu \over {2R}}\,\!</math>

Thus the net extra specific energy needed compared to just raising the spacecraft into space is between 0 and <math>\mu \over{2R}\,\!</math>.

==Speed, range, and altitude==
To minimize the required [[delta-v]] (an [[astrodynamics|astrodynamical]] measure which strongly determines the required [[fuel]]), the high-altitude part of the flight is made with the [[rocket]]s off (this is technically called free-fall even for the upward part of the trajectory). (Compare with [[Oberth effect]].) The maximum [[speed]] in a flight is attained at the lowest altitude of this free-fall trajectory, both at the start and at the end of it.{{cn|date=May 2024}}

If one's goal is simply to "reach space", for example in competing for the [[Ansari X Prize]], horizontal motion is not needed. In this case the lowest required delta-v, to reach 100&nbsp;km altitude, is about 1.4&nbsp;[[km/s]]. Moving slower, with less free-fall, would require more delta-v.{{cn|date=May 2024}}

Compare this with orbital spaceflights: a low Earth orbit (LEO), with an altitude of about 300&nbsp;km, needs a speed around 7.7&nbsp;km/s, requiring a delta-v of about 9.2&nbsp;km/s. (If there were no atmospheric drag the theoretical minimum delta-v would be 8.1&nbsp;km/s to put a craft into a 300-kilometer high orbit starting from a stationary point like the South Pole. The theoretical minimum can be up to 0.46&nbsp;km/s less if launching eastward from near the equator.){{cn|date=May 2024}}

For sub-orbital spaceflights covering a horizontal distance the maximum speed and required delta-v are in between those of a vertical flight and a LEO. The maximum speed at the lower ends of the trajectory are now composed of a horizontal and a vertical component. The higher the horizontal [[distance]] covered, the greater the horizontal speed will be. (The vertical velocity will increase with distance for short distances but will decrease with distance at longer distances.) For the [[V-2 rocket]], just reaching space but with a range of about 330&nbsp;km, the maximum speed was 1.6&nbsp;km/s. [[Scaled Composites SpaceShipTwo]] which is under development will have a similar free-fall orbit but the announced maximum speed is 1.1&nbsp;km/s (perhaps because of engine shut-off at a higher altitude).{{cn|date=May 2024}}{{update inline|date=June 2024}}

For larger ranges, due to the elliptic orbit the maximum altitude can be much more than for a LEO. On a 10,000-kilometer intercontinental flight, such as that of an intercontinental ballistic missile or possible future [[commercial spaceflight]], the maximum speed is about 7&nbsp;km/s, and the maximum altitude may be more than 1300&nbsp;km.
Any [[spaceflight]] that returns to the surface, including sub-orbital ones, will undergo [[atmospheric reentry]]. The speed at the start of the reentry is basically the maximum speed of the flight. The [[aerodynamic heating]] caused will vary accordingly: it is much less for a flight with a maximum speed of only 1&nbsp;km/s than for one with a maximum speed of 7 or 8&nbsp;km/s.{{cn|date=May 2024}}

The minimum delta-v and the corresponding maximum altitude for a given range can be calculated, ''d'', assuming a spherical Earth of circumference {{val|40000|u=km}} and neglecting the Earth's rotation and atmosphere. Let θ be half the angle that the projectile is to go around the Earth, so in degrees it is 45°×''d''/{{val|10000|u=km}}. The minimum-delta-v trajectory corresponds to an ellipse with one focus at the centre of the Earth and the other at the point halfway between the launch point and the destination point (somewhere inside the Earth). (This is the orbit that minimizes the semi-major axis, which is equal to the sum of the distances from a point on the orbit to the two foci. Minimizing the semi-major axis minimizes the [[specific orbital energy]] and thus the delta-v, which is the speed of launch.) Geometrical arguments lead then to the following (with ''R'' being the radius of the Earth, about 6370&nbsp;km):

<math display="block">\text{major axis} = (1 + \sin\theta)R</math>

<math display="block">\text{minor axis} = R\sqrt{2\left(\sin\theta + \sin^2\theta\right)} = \sqrt{R\sin(\theta)\text{semi-major axis}}</math>

<math display="block">\text{distance of apogee from centre of Earth} = \frac{R}{2}(1 + \sin\theta + \cos\theta)</math>

<math display="block">\text{altitude of apogee above surface} = \left(\frac{\sin\theta}{2} - \sin^2\frac{\theta}{2}\right)R = \left(\frac{1}{\sqrt{2}}\sin\left(\theta + \frac{\pi}{4}\right) - \frac{1}{2}\right)R</math>

The altitude of apogee is maximized (at about 1320&nbsp;km) for a trajectory going one quarter of the way around the Earth ({{val|10000|u=km}}). Longer ranges will have lower apogees in the minimal-delta-v solution.

<math display="block">\text{specific kinetic energy at launch} = \frac{\mu}{R} - \frac\mu\text{major axis} = \frac{\mu}{R}\frac{\sin\theta}{1 + \sin\theta}</math>

<math display="block">\Delta v = \text{speed at launch} = \sqrt{2\frac{\mu}{R}\frac{\sin\theta}{1 + \sin\theta}} = \sqrt{2gR\frac{\sin\theta}{1 + \sin\theta}}</math>

(where ''g'' is the acceleration of gravity at the Earth's surface). The Δ''v'' increases with range, leveling off at 7.9&nbsp;km/s as the range approaches {{val|20000|u=km}} (halfway around the world). The minimum-delta-v trajectory for going halfway around the world corresponds to a circular orbit just above the surface (of course in reality it would have to be above the atmosphere). See lower for the time of flight.

An [[intercontinental ballistic missile]] is defined as a missile that can hit a target at least 5500&nbsp;km away, and according to the above formula this requires an initial speed of 6.1&nbsp;km/s. Increasing the speed to 7.9&nbsp;km/s to attain any point on Earth requires a considerably larger missile because the amount of fuel needed goes up exponentially with delta-v (see [[Rocket equation]]).

The initial direction of a minimum-delta-v trajectory points halfway between straight up and straight toward the destination point (which is below the horizon). Again, this is the case if the Earth's rotation is ignored. It is not exactly true for a rotating planet unless the launch takes place at a pole.<ref name="tpticbm">{{cite journal |last1=Blanco |first1=Philip |title=Modeling ICBM Trajectories Around a Rotating Globe with Systems Tool Kit |journal=The Physics Teacher |date=September 2020 |volume=58 |issue=7 |pages=494–496 |doi=10.1119/10.0002070 |bibcode=2020PhTea..58..494B|s2cid=225017449 }}</ref>

==Flight duration==
In a vertical flight of not too high altitudes, the time of the free-fall is both for the upward and for the downward part the maximum speed divided by the [[standard gravity|acceleration of gravity]], so with a maximum speed of 1&nbsp;km/s together 3 minutes and 20 seconds. The duration of the [[flight]] phases before and after the free-fall can vary.{{cn|date=May 2024}}

For an intercontinental flight the [[boost phase]] takes 3 to 5 minutes, the free-fall (midcourse phase) about 25 minutes. For an ICBM the atmospheric reentry phase takes about 2 minutes; this will be longer for any soft landing, such as for a possible future commercial flight.{{cn|date=May 2024}} [[SpaceX_Starship_integrated_flight_test_4|Test flight 4 of the SpaceX 'Starship']] performed such a flight with a lift off from Texas and a simulated soft touchdown in the Indian Ocean 66 minutes after liftoff.

Sub-orbital flights can last from just seconds to days. [[Pioneer 1]] was [[NASA]]'s first [[space probe]], intended to reach the [[Moon]]. A partial failure caused it to instead follow a sub-orbital trajectory, reentering the Earth's atmosphere 43 hours after launch.<ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1958-007A |title=Pioneer 1 - NSSDC ID: 1958-007A |publisher=NASA NSSDC}}</ref>

To calculate the time of flight for a minimum-delta-v trajectory, according to [[Kepler's third law]], the period for the entire orbit (if it did not go through the Earth) would be:

<math display="block">\text{period} = \left(\frac{\text{semi-major axis}}{R}\right)^\frac{3}{2} \times \text{period of low Earth orbit} = \left(\frac{1 + \sin\theta}2\right)^\frac{3}{2}2\pi\sqrt{\frac{R}{g}}</math>

Using [[Kepler's second law]], we multiply this by the portion of the area of the ellipse swept by the line from the centre of the Earth to the projectile:

<math display="block">\text{area fraction} = \frac{1}{\pi}\arcsin\sqrt{\frac{2\sin\theta}{1 + \sin\theta}} + \frac{2\cos\theta\sin\theta}{\pi\text{(major axis)(minor axis)}}</math>

<math display="block">\begin{align}
  \text{time of flight}
    &= \left(\left(\frac{1 + \sin\theta}2\right)^\frac{3}{2}\arcsin\sqrt{\frac{2\sin\theta}{1 + \sin\theta}} + \frac{1}{2}\cos\theta\sqrt{\sin\theta}\right)2\sqrt\frac{R}{g} \\
    &= \left(\left(\frac{1 + \sin\theta}2\right)^\frac{3}{2}\arccos\frac{\cos\theta}{1 + \sin\theta} + \frac{1}{2}\cos\theta\sqrt{\sin\theta}\right)2\sqrt\frac{R}{g} \\
\end{align}</math>

This gives about 32 minutes for going a quarter of the way around the Earth, and 42 minutes for going halfway around. For short distances, this expression is [[asymptotic]] to <math>\sqrt{2d/g}</math>.

From the form involving arccosine, the derivative of the time of flight with respect to ''d'' (or θ) goes to zero as ''d'' approaches {{val|20000|u=km}} (halfway around the world). The derivative of Δ''v'' also goes to zero here. So if ''d'' = {{val|19000|u=km}}, the length of the minimum-delta-v trajectory will be about {{val|19500|u=km}}, but it will take only a few seconds less time than the trajectory for ''d'' = {{val|20000|u=km}} (for which the trajectory is {{val|20000|u=km}} long).

==Flight profiles==
[[File:Mr3-flight-timeline-simple.png|thumb|upright=1.5|Profile for the first crewed American sub-orbital flight, 1961. Launch rocket lifts the spacecraft for the first 2:22 minutes. Dashed line: zero gravity.]]
[[File:Science and Mechanics Nov 1931 cover.jpg|thumb|''[[Science and Mechanics]]'' cover of November 1931, showing a proposed sub-orbital spaceship that would reach an altitude {{convert|700|mi|km}} on its one hour trip from Berlin to New York.]]

While there are a great many possible sub-orbital flight profiles, it is expected that some will be more common than others.

[[File:X-15.jpg|thumb|The X-15 (1958–1968) was launched to an altitude of 13.7 km by a [[Boeing B-52 Stratofortress|B-52]] [[mother ship|mothership]], lifted itself to approximately 100 km, and then glided to the ground.]]

===Ballistic missiles===
The first sub-orbital vehicles which reached space were [[ballistic missiles]]. The first ballistic missile to reach space was the German [[V-2 rocket|V-2]], the work of the scientists at [[Peenemünde]], on October 3, 1942, which reached an altitude of {{convert|53|mi|km}}.<ref>Germany's V-2 Rocket, Kennedy, Gregory P.</ref> Then in the late 1940s the US and [[USSR]] concurrently developed missiles all of which were based on the V-2 Rocket, and then much longer range Intercontinental Ballistic Missiles (ICBMs). There are now many countries who possess ICBMs and even more with shorter range [[IRBM|Intermediate Range Ballistic Missiles]] (IRBMs).{{cn|date=May 2024}}

===Tourist flights===
[[Space tourism|Sub-orbital tourist flights]] will initially focus on attaining the altitude required to qualify as reaching space. The flight path will be either vertical or very steep, with the spacecraft landing back at its take-off site.

The spacecraft will shut off its [[engine]]s well before reaching maximum altitude, and then coast up to its highest point. During a few minutes, from the point when the engines are shut off to the point where the atmosphere begins to slow down the downward acceleration, the passengers will experience [[weightlessness]].

[[Megaroc]] had been planned for sub-orbital spaceflight by the [[British Interplanetary Society]] in the 1940s.<ref>{{cite web|url=http://www.bbc.com/future/story/20150824-how-a-nazi-rocket-could-have-put-a-briton-in-space|title=How a Nazi rocket could have put a Briton in space|first=Richard|last=Hollingham|website=bbc.com|access-date=4 May 2018|url-status=live|archive-url=https://web.archive.org/web/20161114032515/http://www.bbc.com/future/story/20150824-how-a-nazi-rocket-could-have-put-a-briton-in-space|archive-date=14 November 2016}}</ref><ref>{{cite web|url=http://www.bis-space.com/what-we-do/projects/megaroc|title=Megaroc|website=www.bis-space.com|access-date=4 May 2018|url-status=live|archive-url=https://web.archive.org/web/20161030133900/http://www.bis-space.com/what-we-do/projects/megaroc|archive-date=30 October 2016}}</ref>

In late 1945, a group led by M. Tikhonravov K. and N. G. Chernysheva at the Soviet NII-4 academy (dedicated to rocket artillery science and technology), began work on a stratospheric rocket project, [[Project VR-190|VR-190]], aimed at vertical flight by a crew of two pilots, to an altitude of 200&nbsp;km (65,000 ft) using captured [[V-2 rocket|V-2]].<ref>{{Cite book |author=Anatoli I. Kiselev |author2=Alexander A. Medvedev| author3=Valery A. Menshikov |title=Astronautics: Summary and Prospects |translator=V. Sherbakov |translator2=N. Novichkov |translator3=A. Nechaev |publisher=Springer Science & Business Media|date=December 2012|pages=1–2|isbn=9783709106488}}</ref>

In 2004, a number of companies worked on vehicles in this class as entrants to the Ansari X Prize competition. The [[Scaled Composites SpaceShipOne]] was officially declared by [[Richard A. Searfoss|Rick Searfoss]] to have won the competition on October 4, 2004, after completing two flights within a two-week period.

In 2005, [[Richard Branson|Sir Richard Branson]] of the [[Virgin Group]] announced the creation of [[Virgin Galactic]] and his plans for a 9-seat capacity SpaceShipTwo named [[VSS Enterprise|VSS ''Enterprise'']]. It has since been completed with eight seats (one pilot, one co-pilot and six passengers) and has taken part in captive-carry tests and with the first mother-ship [[WhiteKnightTwo]], or [[VMS Eve|VMS ''Eve'']]. It has also completed solitary glides, with the movable tail sections in both fixed and "feathered" configurations.  The [[hybrid rocket]] motor has been fired multiple times in ground-based test stands, and was fired in a powered flight for the second time on 5 September 2013.<ref>{{cite web |url=http://www.scaled.com/projects/test_logs/35/model_339_spaceshiptwo |title=Scaled Composites: Projects - Test Logs for SpaceShipTwo |access-date=2013-08-14 |url-status=live |archive-url=https://web.archive.org/web/20130816140953/http://www.scaled.com/projects/test_logs/35/model_339_spaceshiptwo |archive-date=2013-08-16 }}</ref> Four additional SpaceShipTwos have been ordered and will operate from the new [[Spaceport America]]. Commercial flights carrying passengers were expected in 2014, but became cancelled due to the [[VSS Enterprise crash|disaster during SS2 PF04 flight]]. Branson stated, "[w]e are going to learn from what went wrong, discover how we can improve safety and performance and then move forwards together."<ref>"Branson on Virgin Galactic crash: 'Space is hard – but worth it'". CNET. Retrieved August 1, 2015.</ref>

===Scientific experiments===
A major use of sub-orbital vehicles today is as [[scientific]] [[sounding rocket]]s. Scientific sub-orbital flights began in the 1920s when [[Robert H. Goddard]] launched the first [[liquid fuel]]ed rockets, however they did not reach [[space]] altitude. In the late 1940s, captured German [[V-2 rocket|V-2 ballistic missiles]] were converted into [[V-2 sounding rocket]]s which helped lay the foundation for modern sounding rockets.<ref>{{Cite web|title = ch2|url = https://history.nasa.gov/SP-4401/ch2.htm|website = history.nasa.gov|access-date = 2015-11-28|url-status = live|archive-url = http://archive.wikiwix.com/cache/20151129091504/https://history.nasa.gov/SP-4401/ch2.htm|archive-date = 2015-11-29}}</ref> Today there are dozens of different sounding rockets on the market, from a variety of suppliers in various countries. Typically, researchers wish to conduct experiments in [[microgravity]] or above the atmosphere.

===Sub-orbital transportation===
Research, such as that done for the [[X-20 Dyna-Soar]] project suggests that a semi-ballistic sub-orbital flight could travel from Europe to North America in less than an hour.

However, the size of rocket, relative to the payload, necessary to achieve this, is similar to an ICBM. ICBMs have delta-v's somewhat less than orbital; and therefore would be somewhat cheaper than the costs for reaching orbit, but the difference is not large.<ref>{{cite web|url=http://www.thespacereview.com/article/1118/1|title=The Space Review: Point-to-point suborbital transportation: sounds good on paper, but...|website=www.thespacereview.com|access-date=4 May 2018|url-status=live|archive-url=https://web.archive.org/web/20170801074751/http://www.thespacereview.com/article/1118/1|archive-date=1 August 2017}}</ref>

Due to the high cost of spaceflight, suborbital flights are likely to be initially limited to high value, very high urgency cargo deliveries such as [[courier]] flights, [[military]] fast-response operations or [[space tourism]].{{opinion|date=April 2012}}

The [[SpaceLiner]] is a hypersonic [[suborbital spaceplane]] concept that could transport 50 passengers from [[Australia]] to [[Europe]] in 90 minutes or 100 passengers from Europe to [[California]] in 60 minutes.<ref>{{Cite journal|doi=10.1016/j.actaastro.2010.01.020| author = Sippel, M. | title = Promising roadmap alternatives for the SpaceLiner |journal = Acta Astronautica |issue = 11–12 |volume = 66 |date = 2010| pages = 1652–1658 | bibcode = 2010AcAau..66.1652S | url = https://elib.dlr.de/64605/1/AA3731.pdf }}</ref> The main challenge lies in increasing the reliability of the different components, particularly the engines, in order to make their use for passenger transportation on a daily basis possible.

[[SpaceX]] is potentially considering using their [[SpaceX Starship|Starship]] as a sub-orbital point-to-point transportation system.<ref name=trati20190530>{{cite news |last=Ralph|first=Eric |url=https://www.teslarati.com/spacex-elon-musk-wants-starship-spaceliners/ |title=SpaceX CEO Elon Musk wants to use Starships as Earth-to-Earth transports |work=Teslarati |date=30 May 2019 |access-date=31 May 2019 }}</ref>

==Notable uncrewed sub-orbital spaceflights==
* The first sub-orbital space flight was on 20 June 1944, when [[MW 18014]], a [[V-2 rocket|V-2 test rocket]], launched from [[Peenemünde]] in Germany and reached 176 kilometres altitude.<ref>Walter Dornberger, Moewig, Berlin 1984. {{ISBN|3-8118-4341-9}}.</ref>
* [[Bumper (rocket)|Bumper]] 5, a two-stage rocket launched from the [[White Sands Proving Grounds]]. On 24 February 1949 the upper stage reached an altitude of {{convert|248|mi|km}} and a speed of {{convert|7,553|ft/s|m/s Mach}}.<ref>
{{cite web | url = http://www.wsmr.army.mil/pao/FactSheets/bump.htm | title = Bumper Project | publisher = White Sands Missile Range | url-status = dead | archive-url = https://web.archive.org/web/20080110163113/http://www.wsmr.army.mil/pao/FactSheets/bump.htm | archive-date = 2008-01-10 }}</ref>
* [[Albert II (monkey)|Albert II]], a male [[rhesus macaque]], became the first mammal in space on 14 June 1949 in a sub-orbital flight from [[Holloman Air Force Base]] in New Mexico to an altitude of 83 miles (134&nbsp;km) aboard a U.S. [[V-2 sounding rocket]].
* USSR – [[Energia (rocket)|Energia]], 15 May 1987, a [[Polyus (spacecraft)|Polyus]] payload which failed to reach orbit
* SpaceX [[Starship flight test 7|IFT-7]], 16 January 2025, a [[SpaceX Starship|Starship]] [[List of Starship launches|flight test]] which blew up during ascent, forcing airline flights to alter course to avoid falling debris and setting back Elon Musk's flagship rocket program.<ref>{{cite web | url = https://arstechnica.com/space/2025/01/fire-destroys-starship-on-its-seventh-test-flight-raining-debris-from-space/ | title = Fire destroys Starship on its seventh test flight, raining debris from space | publisher = Ars Technica }}</ref><ref>{{cite web | url = https://www.reuters.com/technology/space/spacex-launches-seventh-starship-mock-satellite-deployment-test-2025-01-16/ | title = SpaceX's Starship explodes in flight test, forcing airlines to divert | publisher = Reuters }}</ref> There were also numerous reports of damage on the ground.<ref>{{cite web | url = https://edition.cnn.com/2025/01/17/science/spacex-starship-explosion-investigation/index.html | title = Regulators are investigating reports of property damage from SpaceX Starship’s explosion | publisher = CNN }}</ref> It is, to date, the most massive object launched into a sub-orbital trajectory.

==Crewed sub-orbital spaceflights==
Above 100&nbsp;km (62.14&nbsp;mi) in altitude.{{efn|Flights exceeding 80km but not 100km, including those flown by [[SpaceShipTwo]], are recognized as spaceflight by the United States.}}
{| class="wikitable"
!
!Date (GMT)
!Mission
!Crew
!Country
!Remarks
|-
|1
|1961-05-05
|[[Mercury-Redstone 3]]
|[[Alan Shepard]]
|{{USA}}
|First crewed sub-orbital spaceflight, first American in space
|-
|2
|1961-07-21
|[[Mercury-Redstone 4]]
|[[Virgil Grissom]]
|{{USA}}
|Second crewed sub-orbital spaceflight, second American in space
|-
|3
|1963-07-19
|[[X-15 Flight 90]]
|[[Joseph A. Walker]]
|{{USA}}
|First winged craft in space
|-
|4
|1963-08-22
|[[X-15 Flight 91]]
|Joseph A. Walker
|{{USA}}
|First person and spacecraft to make two flights into space
|-
|5
|1975-04-05
|[[Soyuz 18a]]
|[[Vasili Lazarev]]<br />[[Oleg Grigoryevich Makarov|Oleg Makarov]]
|{{USSR}}
|Failed orbital launch. Aborted after malfunction during stage separation
|-
|6
|2004-06-21
|[[SpaceShipOne flight 15P]]
|[[Mike Melvill]]
|{{USA}}
|First commercial spaceflight
|-
|7
|2004-09-29
|[[SpaceShipOne flight 16P]]
|Mike Melvill
|{{USA}}
|First of two flights to win [[Ansari X-Prize]]
|-
|8
|2004-10-04
|[[SpaceShipOne flight 17P]]
|[[Brian Binnie]]
|{{USA}}
|Second X-Prize flight, clinching award
|-
|9
|2021-07-20
|[[Blue Origin NS-16]]
|[[Jeff Bezos]]<br />[[Mark Bezos]]<br />[[Wally Funk]]<br />[[Oliver Daemen]]
|{{USA}}
|First crewed Blue Origin flight
|-
|10
|2021-10-13
|[[Blue Origin NS-18]]
|[[Audrey Powers]]<br />[[Chris Boshuizen]]<br />[[Glen de Vries]]<br />[[William Shatner]]
|{{USA}}
|Second crewed Blue Origin flight
|-
|11
|2021-12-11
|[[Blue Origin NS-19]]
|{{nowrap|Laura Shepard Churchley}}<br />[[Michael Strahan]]<br />[[Dylan Taylor (executive)|Dylan Taylor]]<br />Evan Dick<br />[[Lane Bess]]<br />Cameron Bess
|{{USA}}
|Third crewed Blue Origin flight
|-
|12
|2022-03-31
|[[Blue Origin NS-20]]
|{{nowrap|Marty Allen}}<br />Sharon Hagle<br />Marc Hagle<br />[[Jim Kitchen]]<br />George Nield<br />[[Gary Lai]]
|{{USA}}
|Fourth crewed Blue Origin flight
|-
|13
|2022-06-04
|[[Blue Origin NS-21]]
|Evan Dick<br />[[Katya Echazarreta]]<br />[[Hamish Harding]]<br />Victor Correa Hespanha<br />[[Jaison Robinson]]<br />[[Victor Vescovo]]
|{{USA}}
|Fifth crewed Blue Origin flight
|-
|14
|2022-08-04
|[[Blue Origin NS-22]]
|[[Coby Cotton]]<br />[[Mário Ferreira]]<br />[[Vanessa O'Brien]]<br />Clint Kelly III<br />Sara Sabry<br />Steve Young
|{{USA}}
|Sixth crewed Blue Origin flight
|-
|15
|2024-05-19
|[[Blue Origin NS-25]]
|Mason Angel<br />Sylvain Chiron<br />[[Ed Dwight]]<br />[[Kenneth Hess]]<br />Carol Schaller<br />Gopichand Thotakura
|{{USA}}
|Seventh crewed Blue Origin flight
|-
|16
|2024-08-29
|[[Blue Origin NS-26]]
|Nicolina Elrick<br/>Rob Ferl<br/>Eugene Grin<br/>Eiman Jahangir<br/>Karsen Kitchen<br/>Ephraim Rabin
|{{USA}}
|Eighth crewed Blue Origin flight 
|-
|17
|2024-11-22
|[[Blue Origin NS-28]]
|Henry (Hank) Wolfond<br/>Austin Litteral<br/>James (J.D.) Russell<br/>Sharon Hagle<br/>Marc Hagle<br/>[[Emily Calandrelli]]
|{{USA}}
|Ninth crewed Blue Origin flight 
|-
|18
|2024-02-25
|[[Blue Origin NS-30]]
|[[Lane Bess]]<br />[[Jesús Calleja]]<br />Tushar Shah<br />Richard Scott<br />Elaine Chia Hyde<br />Robert Wilson 
|{{USA}}
|Tenth crewed Blue Origin flight 
|}
{{suborbital_spaceflight_timeline.svg}}

==Future of crewed sub-orbital spaceflight==
[[Private companies]] such as [[Virgin Galactic]], [[Armadillo Aerospace]] (reinvented as Exos Aerospace), [[Airbus]],<ref>{{cite news|url=https://www.bbc.co.uk/news/science-environment-27686906|title=Airbus drops model 'space jet'|first=Jonathan|last=Amos|work=BBC News|date=3 June 2014|access-date=4 May 2018|url-status=live|archive-url=https://web.archive.org/web/20180504004642/http://www.bbc.co.uk/news/science-environment-27686906|archive-date=4 May 2018}}</ref> [[Blue Origin]] and [[Masten Space Systems]] are taking an interest in sub-orbital spaceflight, due in part to ventures like the Ansari X Prize. [[National Aeronautics and Space Administration|NASA]] and others are experimenting with [[scramjet]]-based [[hypersonic]] aircraft which may well be used with flight profiles that qualify as sub-orbital spaceflight. [[Non-profit]] entities like [[ARCASPACE]] and [[Copenhagen Suborbitals]] also attempt [[rocket]]-based launches.

==Suborbital spaceflight projects==
{{Portal|Spaceflight}}
* [[Canadian Arrow]]
* [[CORONA (SSTO)|CORONA]]
* [[DH-1 (rocket)]]
* [[Interorbital Systems]]
* [[Lunar Lander Challenge]]
* [[McDonnell Douglas DC-X]]
* [[Project Morpheus]] NASA program to continue developing ALHAT and Q&shy; landers
* [[Quad (rocket)]]
* [[Reusable Vehicle Testing]] program by [[JAXA]]
* [[Rocketplane XP]]
* [[SpaceX reusable launch system development program]]
* [[XCOR Lynx]]

== See also ==

* Levels of spaceflight: Suborbital, [[Orbital spaceflight|orbital]], [[Interplanetary spaceflight|interplanetary]], [[Interstellar travel|interstellar]] and [[Intergalactic travel|intergalatic]]
==Notes==
{{Notelist}}
==References==
{{Reflist}}

{{Spaceflight}}

{{DEFAULTSORT:Sub-orbital spaceflight}}
[[Category:Spaceflight concepts|*]]
[[Category:Suborbital spaceflight| ]]