View source for Nuclear power in space

{{short description|Space exploration using nuclear energy}}
[[File:Kiwi A fire-up.jpg|thumb|The [[Project Rover#Kiwi A|Kiwi-A Prime]] nuclear thermal rocket engine 1960 test at [[Jackass Flats]], Nevada.]]
[[File:PIA16937-MarsCuriosityRover-SelfPortraitAtJohnKlein-20130510.jpg|thumb|Mars ''[[Curiosity (rover)|Curiosity]]'' rover powered by a RTG on Mars. White RTG with fins is visible at far side of rover.]]
'''Nuclear power in space''' is the use of [[nuclear power]] in [[outer space]], typically either small [[nuclear fission|fission]] systems or [[radioactive decay]] for electricity or heat. Another use is for scientific observation, as in a [[Mössbauer spectrometer]]. The most common type is a [[radioisotope thermoelectric generator]], which has been used on many space probes and on crewed lunar missions. Small fission reactors for Earth observation satellites, such as the [[TOPAZ nuclear reactor]], have also been flown.<ref>{{cite book | last = Hyder | first = Anthony K. |author2=R. L. Wiley |author3=G. Halpert |author4=S. Sabripour |author5=D. J. Flood  | title = Spacecraft Power Technologies | publisher = [[Imperial College Press]] | year = 2000 | page = 256 | isbn = 1-86094-117-6}}</ref> A [[radioisotope heater unit]] is powered by radioactive decay and can keep components from becoming too cold to function, potentially over a span of decades.<ref name=doe1>{{cite web|title = Department of Energy Facts: Radioisotope Heater Units|publisher = U.S. Department of Energy, Office of Space and Defense Power Systems|date = December 1998|url = http://saturn.jpl.nasa.gov/spacecraft/safety/rhu.pdf|access-date = March 24, 2010|url-status = dead|archive-url = https://web.archive.org/web/20100527144930/http://saturn.jpl.nasa.gov/spacecraft/safety/rhu.pdf|archive-date = May 27, 2010}}</ref>

The United States tested the [[SNAP-10A]] nuclear reactor in space for 43 days in 1965,<ref name=zaitsev/> with the next test of a nuclear reactor power system intended for space use occurring on 13 September 2012 with the Demonstration Using Flattop Fission (DUFF) test of the [[Kilopower]] reactor.<ref>{{cite web |url=http://www.nasa.gov/centers/glenn/news/pressrel/2012/12-059_fission_prt.htm |title=NASA - Researchers Test Novel Power System for Space Travel - Joint NASA and DOE team demonstrates simple, robust fission reactor prototype |website=Nasa.gov |date=2012-11-26 |access-date=2016-02-23 |archive-date=2016-03-05 |archive-url=https://web.archive.org/web/20160305001012/http://www.nasa.gov/centers/glenn/news/pressrel/2012/12-059_fission_prt.htm |url-status=dead }}</ref>

After a ground-based test of the experimental 1965 [[Romashka reactor]], which used uranium and direct [[thermoelectric]] conversion to electricity,<ref name="Romashka reactor-converter">{{cite journal|last=Ponomarev-Stepnoi|first=N. N.|author2=Kukharkin, N. E. |author3=Usov, V. A. |date=March 2000|title="Romashka" reactor-converter |journal=Atomic Energy|publisher=Springer|location=New York|volume=88|issue=3|pages=178–183|issn=1063-4258|doi=10.1007/BF02673156|s2cid=94174828}}</ref> the USSR sent about 40 nuclear-electric [[US-A|satellites]] into space, mostly powered by the [[BES-5]] reactor. The more powerful TOPAZ-II reactor produced 10 kilowatts of electricity.<ref name=zaitsev>{{cite web|url=http://www.spacedaily.com/reports/Nuclear_Power_In_Space_999.html |title=Nuclear Power In Space |website=Spacedaily.com |access-date=2016-02-23}}</ref>

Examples of concepts that use nuclear power for space propulsion systems include the [[nuclear electric rocket]] (nuclear powered [[ion thruster]](s)), the [[radioisotope rocket]], and radioisotope electric propulsion (REP).<ref>{{cite web|url=http://www.lpi.usra.edu/opag/mcnuttstaif06.pdf |title=Radioisotope Electric Propulsion : Enabling the Decadal Survey Science Goals for Primitive Bodies |website=Lpi.usra.edu |access-date=2016-02-23}}</ref> One of the more explored concepts is the [[nuclear thermal rocket]], which was ground tested in the [[NERVA]] program. [[Nuclear pulse propulsion]] was the subject of [[Project Orion (nuclear propulsion)|Project Orion]].<ref>{{cite web |author1=Everett, C.J. |author2=Ulam S.M. |title=On a Method of Propulsion of Projectiles by Means of External Nuclear Explosions. Part I |publisher=Los Alamos Scientific Laboratory |date=August 1955 |page=5 |url=https://apps.dtic.mil/sti/pdfs/ADA306631.pdf |archive-url=https://web.archive.org/web/20120725080421/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA306631&Location=U2&doc=GetTRDoc.pdf |url-status=live |archive-date=July 25, 2012 }}</ref>

==Hazards and regulations==
[[File:Nimbus B RTG on the ocean floor.jpg|thumb|Intact SNAP-19 fuel capsule is shown among debris on [[Pacific Ocean]] floor, resulting from the aborted launch of a Nimbus B.]]

{{CSS image crop|Image=NaK_Alloy.jpg|bSize=220|cWidth=220|cHeight=240|oTop=140|Align=right|Description=Sodium-potassium (NaK) alloy droplets similar to those released in high Earth orbit by the Soviet RORSAT program's fission reactors.}}

=== Hazards ===
After the ban of [[Militarisation of space|nuclear weapons in space]] by the [[Outer Space Treaty]] in 1967, nuclear power has been discussed at least since 1972 as a sensitive issue by states.<ref name="Space Legal Issues 2018">{{cite web |date=2019-07-24 |title=Nuclear Power Sources in Space |url=https://www.spacelegalissues.com/principles-relevant-to-the-use-of-nuclear-power-sources-in-outer-space/ |access-date=2021-06-04 |website=Space Legal Issues |archive-date=2021-06-22 |archive-url=https://web.archive.org/web/20210622161847/https://www.spacelegalissues.com/principles-relevant-to-the-use-of-nuclear-power-sources-in-outer-space/ |url-status=dead }}</ref> Space nuclear power sources may experience accidents during launch, operation, and end-of-service phases, resulting in the exposure of nuclear power sources to extreme physical conditions and the release of radioactive materials into the Earth's atmosphere and surface environment.<ref name=":0">{{Citation |last1=Tchouaso |first1=Modeste Tchakoua |title=Space nuclear power |date=2023 |work=Photovoltaics for Space |pages=443–488 |url=https://doi.org/10.1016/B978-0-12-823300-9.00014-5 |access-date=2024-03-21 |publisher=Elsevier |doi=10.1016/b978-0-12-823300-9.00014-5 |isbn=978-0-12-823300-9 |last2=Alam |first2=Tariq Rizvi |last3=Prelas |first3=Mark Antonio}}</ref> For example, all Radioisotope Power Systems (RPS) used in space missions have utilized Pu-238. [[Plutonium-238]] is a radioactive element that emits alpha particles. Although [[NASA]] states that it exists in spacecraft in a form that is not readily absorbed and poses little to no chemical or toxicological risk upon entering the human body (e.g. in the design of American spacecraft, plutonium dioxide exists in ceramic form to prevent inhalation or ingestion by humans, and it is placed within strict safety protection systems), it cannot be denied that it may be released and dispersed into the environment, posing hazards to both the environment and human health.<ref>{{Cite web |title=About Plutonium-238 {{!}} About RPS |url=https://rps.nasa.gov/about-rps/about-plutonium-238 |access-date=2024-03-21 |website=NASA RPS: Radioisotope Power Systems |language=en}}</ref> Pu-238 primarily accumulates in the lungs, liver, and bones through inhalation of powdered form, thereby posing risks to human health.<ref>{{Cite web |last=Agency for Toxic Substances and Diseases Registry |title=Plutonium {{!}} Public Health Statement {{!}} ATSDR |url=https://wwwn.cdc.gov/tsp/phs/phs.aspx?phsid=646&toxid=119 |access-date=2024-03-21 |website=wwwn.cdc.gov}}</ref>

==== Accidents within the atmosphere ====
There have been several environmental accidents related to space nuclear power in history.

In 1964, a [[Thor-Ablestar]] rocket carrying the [[Transit (satellite)|Transit 5BN-3]] satellite failed to reach orbit, destroying the satellite in re-entry over the southern hemisphere. Its one kilogram of plutonium-238 fuel within the [[SNAP-9A]] RTG was released into the stratosphere. A 1972 Department of Energy soil sample report attributed 13.4 [[kilocurie]]s of Pu-238 to the accident, from the one kilogram's 17 kilocuries total. This was contrasted to the 11,600 kilocuries of [[strontium-90]] deposited by all nuclear weapons testing.<ref>{{Cite journal |last1=Hardy, Jr. |first1=E. P. |last2=Krey |first2=P. W. |last3=Volchok |first3=H. L. |date=1972-01-01 |title=Global Inventory and Distribution of 238-Pu from SNAP-9A |url=https://www.osti.gov/biblio/4689831 |journal=U.S. Department of Energy – Office of Scientific and Technical Information |language=English |doi=10.2172/4689831 |osti=4689831}}</ref>

In May 1968, a [[Thor-Agena]] rocket carrying the [[Nimbus B]] satellite was destroyed by a guidance error. Its plutonium [[SNAP-19]] RTG was recovered intact, without leakage from the Pacific sea floor, refurbished, and flown on [[Nimbus 3]].<ref name="NASA nssdc2">{{cite web |title=Nimbus B |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=NIMBS-B |access-date=June 5, 2018 |publisher=NASA Goddard Space Flight Center}}</ref>

In April 1970, the Apollo 13 lunar mission was aborted due to an oxygen tank explosion in the spacecraft's service module. Upon reentering the atmosphere, the lunar module equipped with the [[SNAP-27]] RTG exploded and crashed into the South Pacific Ocean, with no leakage of nuclear fuel.<ref name=":0" /> This is the only intact flown nuclear system that remains on Earth without recovery.{{Citation needed|date=August 2024}}

In early 1978, the Soviet spacecraft [[Kosmos 954]], powered by a 45-kilogram highly enriched uranium reactor, went into an uncontrolled descent. Due to the unpredictable impact point, preparations were made for potential contamination of inhabited areas. This event underscored the potential danger of space objects containing radioactive materials, emphasizing the need for strict international emergency planning and information sharing in the event of space nuclear accidents. It also led to the intergovernmental formulation of emergency protocols, such as [[Operation Morning Light]], where Canada and the United States jointly recovered 80 radioactive fragments within a 600-kilometer range in the Canadian Northwest Territories. COSMOS 954 became the first example for global emergency preparedness and response arrangements for satellites carrying nuclear power sources.<ref>{{Cite web |last=International Atomic Energy Agency |date=2020-10-28 |title=Ensuring Safety on Earth from Nuclear Sources in Space |url=https://www.iaea.org/newscenter/news/ensuring-safety-on-earth-from-nuclear-sources-in-space |access-date=2024-03-21 |website=www.iaea.org |language=en}}</ref>

==== NaK droplet debris ====
The majority of [[List of nuclear power systems in space|nuclear power systems launched into space]] remain in [[graveyard orbit]]s around Earth. Between 1980 and 1989, the [[BES-5]] and [[TOPAZ nuclear reactor|TOPAZ-I]] fission reactors of the Soviet [[RORSAT]] program suffered leakages of their liquid [[sodium–potassium alloy]] coolant. Each reactor lost on average 5.3 kilograms of its 13 kilogram total coolant, totaling 85 kilograms across 16 reactors. A 2017 ESA paper calculated that, while smaller droplets quickly decay, 65 kilograms of coolant still remain in centimeter-sized droplets around 800&nbsp;km altitude orbits, comprising 10% of the space debris in that size range.<ref name="u407">{{cite web |last=Wiedemann |first=Carsten |last2=Gamper |first2=Eduard |last3=Horstmann |first3=Andre |last4=Braun |first4=Vitali |last5=Stoll |first5=Enrico |date=2017 |title=The contribution of NaK droplets to the space debris environment |url=https://conference.sdo.esoc.esa.int/proceedings/sdc7/paper/367#:~:text=Sodium%2Dpotassium%20droplets%20are%20a,Only%20the%20size%20is%20different. |access-date=2024-08-03 |website=ESA Proceedings Database |language=de}}</ref>

==== Trapped-positron problem ====
[[File:Structure of the magnetosphere mod.svg|thumb|The structure of Earth's magnetosphere. Fission-produced trapped positrons precess along the innermost red field lines and can interfere with instruments on satellites.]]
[[File:Illustration of Cosmos 1818 and Cosmos 1867.jpg|thumb|Diagram of Kosmos 1818 and Kosmos 1867, which carried the TOPAZ-I fission reactors]]
{{multiple image
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 | image1 = Smm.jpg
 | alt1 = Illustration of NASA's Solar Maximum Mission satellite
 | image2 = Astro-c_ginga.png
 | alt2 = Illustration of ISAS' Ginga X-ray astronomy satellite
 | footer = The [[Solar Maximum Mission]] and [[Ginga (satellite)|Ginga]] satellites, both carrying gamma ray telescopes affected by reactor positron pollution
}}
Orbital fission reactors are a source of significant interference for orbital [[Gamma-ray astronomy|gamma ray observatories]]. Unlike RTGs which largely rely on energy from [[alpha decay]], fission reactors produce significant [[gamma radiation]], with the uranium-235 chain releasing 6.3% of its total energy as prompt (shown below) and delayed (daughter product decay) gamma rays:<ref name="kayelaby">[https://web.archive.org/web/20190505175631/http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html Nuclear fission and fusion, and neutron interactions], National Physical Laboratory Archive.</ref>

<math chem="">\begin{array}{r}
^1_0\text{n}\ +\ ^{235}_{92}\text{U}\longrightarrow\  ^{141}_{56}\text{Ba}\ +\ ^{92}_{36}\text{Kr}\ +\ 3\ ^{1}_{0}\text{n}\ + \gamma
\end{array}
</math>

[[Pair production]] occurs as these gamma rays interact with reactor or adjacent material, ejecting electrons and [[positron]]s into space:

<math chem="">
\gamma + \text{Z} \longrightarrow\ e^+ + e^- + \text{Z}\ 
</math>

These electrons and positrons then become trapped in the magnetosphere's [[flux tube]]s, which carry them through a range of orbital altitudes, where the positrons can annihilate with the structure of other satellites, again producing gamma rays:

<math chem="">
e^+ + e^- \longrightarrow \gamma\ + \gamma   
</math>

These gamma rays can interfere with satellite instruments. This most notably occurred in 1987, when the [[TOPAZ nuclear reactor|TOPAZ-I nuclear reactors]] (6–10 kWe) aboard the twin [[RORSAT]] test vehicles [[Kosmos 1818]] and [[Kosmos 1867]] affected the gamma ray telescopes aboard [[NASA]]'s [[Solar Maximum Mission]] and the [[University of Tokyo]]/[[Institute of Space and Astronautical Science|ISAS]]' [[Ginga (satellite)|Ginga]]. TOPAZ-I remains the most powerful fission reactor operated in space, with previous Soviet missions using the [[BES-5]] reactor (2–3 kWe) at altitudes well below gamma ray observatories.<ref name="u312">{{cite web |last=Grahn |first=Sven |title=The US-A program (Radar Ocean Reconnaissance Satelites) |url=http://www.svengrahn.pp.se/trackind/RORSAT/RORSAT.html#SYIS89 |access-date=2024-07-27 |website=Sven's Space Place}}</ref>

=== Regulations ===

==== National regulations ====
The presence of space nuclear sources and the potential consequences of nuclear accidents on humans and the environment cannot be ignored. Therefore, there have been strict regulations for the application of nuclear power in outer space to mitigate the risks associated with the use of space nuclear power sources among governments.<ref>{{Cite journal |last=Hussein |first=Esam M.A. |date=December 2020 |title=Emerging small modular nuclear power reactors: A critical review |journal=Physics Open |volume=5 |pages=100038 |doi=10.1016/j.physo.2020.100038 |issn=2666-0326|doi-access=free }}</ref>

For instance, in the United States, safety considerations are integrated into every stage of the design, testing, manufacturing, and operation of space nuclear systems. The [[Nuclear Regulatory Commission|NRC]] oversee the ownership, use, and production of nuclear materials and facilities. The [[Ministry of energy|Department of Energy]] is bound by the [[National Environmental Policy Act]] (NEPA) to consider the environmental impact of nuclear material handling, transportation, and storage.<ref name=":0" /><ref>{{Citation |last=El-Genk |first=Mohamed |title=Safety guidelines for space nuclear reactor power and propulsion systems |date=2010 |work=Space Safety Regulations and Standards |pages=319–370 |url=https://doi.org/10.1016/B978-1-85617-752-8.10026-1 |access-date=2024-03-21 |publisher=Elsevier |doi=10.1016/b978-1-85617-752-8.10026-1|isbn=978-1-85617-752-8 }}</ref> NASA, the Department of Energy, and other federal and local authorities develop comprehensive emergency plans for each launch, including timely public communication. In the event of an accident, monitoring teams equipped with highly specialized support equipment and automated stations are deployed around the launch site to identify potential radioactive material releases, quantify and describe the release scope, predict the quantity and distribution of dispersed material, and develop and recommend protective actions.<ref>{{Cite journal |last1=Barco |first1=Alessandra |last2=Ambrosi |first2=Richard M. |last3=Williams |first3=Hugo R. |last4=Stephenson |first4=Keith |date=June 2020 |title=Radioisotope power systems in space missions: Overview of the safety aspects and recommendations for the European safety case |url=https://doi.org/10.1016/j.jsse.2020.03.001 |journal=Journal of Space Safety Engineering |volume=7 |issue=2 |pages=137–149 |doi=10.1016/j.jsse.2020.03.001 |bibcode=2020JSSE....7..137B |issn=2468-8967}}</ref>

==== International regulations ====
At the global level, following the 1978 COSMOS 954 incident, the international community recognized the need to establish a set of principles and guidelines to ensure the safe use of nuclear power sources in outer space. Consequently, in 1992, the General Assembly adopted resolution 47/68, titled "Principles Relevant to the Use of Nuclear Power Sources in Outer Space."<ref name=":1">{{Cite web |title=NPS Principles |url=https://www.unoosa.org/oosa/en/ourwork/spacelaw/principles/nps-principles.html |access-date=2024-03-21 |website=www.unoosa.org}}</ref> These principles primarily address safety assessment, international information exchange and dialogue, responsibility, and compensation. It stipulates that the principles should be revisited by the [[United Nations Committee on the Peaceful Uses of Outer Space|Committee on the Peaceful Uses of Outer Space]] no later than two years after adoption.<ref name=":1" /> After years of consultation and deliberation, in 2009, the International Safety Framework for Nuclear Power Source Applications in Outer Space was adopted to enhance safety for space missions involving nuclear power sources. It offers guidance for engineers and mission designers, although its effective implementation necessitates integration into existing processes.<ref name=":2">{{Cite journal |last1=Summerer |first1=L. |last2=Wilcox |first2=R.E. |last3=Bechtel |first3=R. |last4=Harbison |first4=S. |date=June 2015 |title=The International Safety Framework for nuclear power source applications in outer space—Useful and substantial guidance |url=https://doi.org/10.1016/j.actaastro.2015.02.007 |journal=Acta Astronautica |volume=111 |pages=89–101 |doi=10.1016/j.actaastro.2015.02.007 |bibcode=2015AcAau.111...89S |issn=0094-5765}}</ref><ref name=":3">{{Cite report |url=https://www.iaea.org/publications/8251/safety-framework-for-nuclear-power-source-applications-in-outer-space |title=Safety Framework for Nuclear Power Source Applications in Outer Space |last=International Atomic Energy Agency |first= |date=2009 |publisher= |pages=1 |language=en}}</ref>

The "Safety Framework" asserts that each nation bears responsibility for the safety of its space nuclear power. Governments and international organizations must justify the necessity of space nuclear power applications compared to potential alternatives and demonstrate their usage based on comprehensive safety assessments, including probabilistic risk analysis, with particular attention to the risk of public exposure to harmful radiation or radioactive materials. Nations also need to establish and maintain robust safety oversight bodies, systems, and emergency preparedness to minimize the likelihood and mitigate the consequences of potential accidents.<ref name=":3" /> Unlike the 1992 "Principles," the "Safety Framework" applies to all types of space nuclear power source development and applications, not just the technologies existing at the time.<ref name=":2" />

In the draft report on the implementation of the Safety Framework for Nuclear Power Source Applications in Outer Space published in 2023, the working group considers that the safety framework has been widely accepted and demonstrated to be helpful for member states in developing and/or implementing national systems and policies to ensure the safe use of nuclear power sources in outer space. Other member states and intergovernmental organizations not currently involved in the utilization of space nuclear power sources also acknowledge and accept the value of this framework, taking into account safety issues associated with such applications.<ref>{{Cite web |title=A/AC.105/C.1/124 - Final report on the implementation of the Safety Framework for Nuclear Power Source Applications in Outer Space and recommendations for potential enhancements of the technical content and scope of the Principles Relevant to the Use of Nuclear Power Sources in Outer Space: Prepared by the Working Group on the Use of Nuclear Power Sources in Outer Space |url=https://www.unoosa.org/oosa/en/oosadoc/data/documents/2023/aac.105c.1/aac.105c.1124_0.html |access-date=2024-03-21 |website=www.unoosa.org}}</ref>

==Benefits==
[[File:Viking Pre-Launch Test Flight - GPN-2003-00047.jpg|thumb|Both the ''[[Viking 1]]'' and ''[[Viking 2]]'' landers used RTGs for power on the surface of Mars. (Viking launch vehicle pictured)]]

=== Power and heat ===
Nuclear power systems function independently of sunlight, which is highly advantageous for [[outer Solar System]] exploration i.e. Jupiter and beyond. All [[List of artificial objects leaving the Solar System|spacecraft leaving the Solar System]], i.e. [[Pioneer 10|''Pioneer'' ''10'']] and [[Pioneer 11|''11'']], [[Voyager 1|''Voyager'' ''1'']] and [[Voyager 2|''2'']], and ''[[New Horizons]]'' use NASA RTGs, as did the outer planet missions of [[Galileo (spacecraft)|''Galileo'']], [[Cassini–Huygens|''Cassini'']], and [[Ulysses (spacecraft)|''Ulysses'']]. However, in part, due to the [[Plutonium-238#U.S. production ceases and resumes|global shortage]] of [[plutonium-238]],<ref>{{cite web |author=David Dickinson |date=March 21, 2013 |title=U.S. to restart plutonium production for deep space exploration |url=http://phys.org/news/2013-03-restart-plutonium-production-deep-space.html |url-status=live |archive-url=https://web.archive.org/web/20210317175454/https://phys.org/news/2013-03-restart-plutonium-production-deep-space.html |archive-date=March 17, 2021 |access-date=February 15, 2015 |publisher=Universe Today}}</ref><ref>{{cite news |last=Greenfieldboyce |first=Nell |title=Plutonium Shortage Could Stall Space Exploration |url=https://www.npr.org/templates/story/story.php?storyId=113223613 |url-status=live |archive-url=https://web.archive.org/web/20200803065501/https://www.npr.org/templates/story/story.php?storyId=113223613 |archive-date=August 3, 2020 |access-date=December 10, 2013 |newspaper=NPR.org |publisher=NPR}}</ref><ref>{{cite news |last=Greenfieldboyce |first=Nell |title=The Plutonium Problem: Who Pays For Space Fuel? |url=https://www.npr.org/2011/11/08/141931325/the-plutonium-problem-who-pays-for-space-fuel |url-status=live |archive-url=https://web.archive.org/web/20180503210442/https://www.npr.org/2011/11/08/141931325/the-plutonium-problem-who-pays-for-space-fuel |archive-date=May 3, 2018 |access-date=December 10, 2013 |newspaper=NPR.org |publisher=NPR}}</ref><ref>{{cite web |last=Wall |first=Mike |date=April 6, 2012 |title=Plutonium Production May Avert Spacecraft Fuel Shortage |url=http://www.space.com/15184-plutonium238-spacecraft-fuel-production.html |url-status=live |archive-url=https://web.archive.org/web/20130703095000/http://www.space.com/15184-plutonium238-spacecraft-fuel-production.html |archive-date=July 3, 2013 |access-date=December 10, 2013 |website=[[Space.com]]}}</ref> and advances in solar efficiency,<ref>{{cite web |date=January 13, 2016 |title=NASA's Juno Spacecraft Breaks Solar Power Distance Record |url=https://www.nasa.gov/feature/jpl/nasas-juno-spacecraft-breaks-solar-power-distance-record |access-date=April 29, 2023 |publisher=NASA}}</ref> the more recent Jupiter missions of [[Juno (spacecraft)|''Juno'']], ''[[Jupiter Icy Moons Explorer]]'', and ''[[Europa Clipper]]'', as well as the [[Jupiter trojan|Jupiter trojan asteroid]] mission of [[Lucy (spacecraft)|''Lucy'']], all opted for large solar arrays despite a relative 4% solar flux at Jupiter's orbit of 5.2 [[Astronomical unit|AU]].

[[Solar power]] is much more commonly used for its low cost and efficiency, primarily in Earth and lunar orbit and for interplanetary missions within the [[inner Solar System]] i.e. missions to Mercury, Venus, Mars and the asteroid belt. However, nuclear power has been used for some of these missions such as the Apollo program's [[SNAP-27]] RTG for lunar surface use, and the [[MMRTG]] on the Mars ''[[Curiosity (rover)|Curiosity]]'' and ''[[Perseverance (rover)|Perseverance]]'' rovers.

Nuclear-based systems can have less mass than solar cells of equivalent power, allowing more compact spacecraft that are easier to orient and direct in space. This makes them useful for radar satellites such as the [[RORSAT]] program deployed by the Soviet Union. In the case of crewed spaceflight, nuclear power concepts that can power both life support and propulsion systems may reduce both cost and flight time.<ref>{{cite web|last=Zaitsev|first=Yury|title=Nuclear Power In Space|url=http://www.spacedaily.com/reports/Nuclear_Power_In_Space_999.html|work=Spacedaily|access-date=22 November 2013}}</ref> Apollo 12 marked the first use of a nuclear power system on a crewed flight, carrying a [[SNAP-27]] RTG to power the [[Apollo Lunar Surface Experiments Package]].{{sfn|Press Kit|pp=33–34}}[[File:RORSAT by Ronald C. Wittmann, 1982.jpg|thumb|Artist's depiction of a [[RORSAT]] radar reconnaissance satellite, typically powered by a [[BES-5]] fission reactor.]]

=== Powering radar systems ===
As active electromagnetic detectors including radar observe a power-distance drop-off of <math chem="">
P \propto R^{-4}   
</math>, comparatively low Earth orbits are desirable.

The Soviet Union did not launch interplanetary missions beyond Mars, and generally developed few RTGs.<ref name="e178">{{cite web |date=2024-08-19 |title=Nuclear Powered Payloads |url=https://space.skyrocket.de/doc_sat/nuclear.htm |access-date=2024-08-19 |website=Gunter's Space Page}}</ref> American RTGs in the 1970s supplied power in the 100 W range.<ref name="Atomic">{{cite web |date=September 2015 |title=Atomic Power in Space II: A History 2015 |url=https://www.inl.gov/wp-content/uploads/2014/10/AtomicPowerInSpaceII-AHistory_2015_Appendices-References1.pdf |accessdate=13 June 2018 |website=inl.gov |publisher=Idaho National Laboratory}}</ref> For the [[RORSAT]] military radar satellites (1967–1988), fission reactors, especially the [[BES-5]], were developed to supply an average of 2&nbsp;kW to the radar. At altitudes averaging 255.3&nbsp;km, they would have rapidly decayed if they had used a large solar array instead.<ref name="u312" />

The later United States [[Lacrosse (satellite)|Lacrosse/Onyx]] radar satellite program, beginning launches in 1988, operated at altitudes of 420–718&nbsp;km. To power radar at this range, a solar array reportedly 45 m in length was operated, speculated to supply 10–20&nbsp;kW.<ref name="k222">{{cite web |date=2024-08-19 |title=Onyx 1, 2, 3, 4, 5 (Lacrosse 1, 2, 3, 4, 5) |url=https://space.skyrocket.de/doc_sdat/onyx.htm |access-date=2024-08-19 |website=Gunter's Space Page}}</ref>

=== Propulsion ===
The following technologies have been proposed and in some cases ground or space-tested for propulsion via nuclear energy.<ref name="a794">{{cite journal |last=Gabrielli |first=Roland Antonius |last2=Herdrich |first2=Georg |date=2015 |title=Review of Nuclear Thermal Propulsion Systems |journal=Progress in Aerospace Sciences |volume=79 |pages=92–113 |doi=10.1016/j.paerosci.2015.09.001}}</ref>
{| class="wikitable sortable"
|+
!Propulsion
!Nuclear 
process
!Cycle{{NoteTag|Open cycles allow the nuclear fuel into the exhaust, closed cycles do not.}}
!Core power analogue
!Tested designs
!Proposed designs 
|-
|[[Nuclear electric rocket]]
|Fission
|Closed
|Space fission reactors, usually [[Liquid metal cooled reactor|liquid metal cooled]]
|{{Flagicon|US}} [[SNAP-10A]], {{Flagicon|USSR}} [[Kosmos 1818]]
|{{Flagicon|US}} [[Project Prometheus]], {{Flagicon|Russia}} [[TEM (nuclear propulsion)|TEM]]
|-
|[[Nuclear thermal rocket]]
|Fission
|Either
|[[High-temperature gas-cooled reactor|High/Very high temperature gas-cooled reactor]]
|{{Flagicon|US}} [[Project Rover]], {{Flagicon|US}} [[NERVA]], {{Flagicon|USSR}}[[RD-0410]]
|{{Flagicon|US}} [[Project Timberwind]], {{Flagicon|US}} [[Demonstration Rocket for Agile Cislunar Operations|Lockheed Martin DRACO]]
|-
|[[Pulsed nuclear thermal rocket]]
|Fission
|Either
|[[TRIGA|TRIGA reactor]]
|
|
|-
|[[Nuclear salt-water rocket]]
|Fission
|Open
|[[Aqueous homogeneous reactor]]
|
|
|-
|[[Gas core reactor rocket]]
|Fission
|Open
|[[Gaseous fission reactor]]
|
|
|-
|[[Nuclear lightbulb]]
|Fission
|Closed
|[[Gaseous fission reactor]]
|
|
|-
|[[Fission-fragment rocket]]
|Fission
|Open
|[[Fission fragment reactor]]
|
|Rotating fuel,<ref>{{cite conference |last1=Chapline |first1=G. |last2=Dickson |first2=P. |last3=Schnitzler |first3=B. |date=18 September 1988 |title=Fission fragment rockets: A potential breakthrough |url=http://www.osti.gov/bridge/servlets/purl/6868318/6868318.pdf |conference=International reactor physics conference |location=Jackson Hole, Wyoming, USA |osti=6868318}}</ref> dusty plasma,<ref>{{cite conference |last1=Clark |first1=R. |last2=Sheldon |first2=R. |date=10–13 July 2005 |title=Dusty Plasma Based Fission Fragment Nuclear Reactor |url=http://www.rbsp.info/rbs/PDF/aiaa05.pdf |conference=41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit |location=Tucson, Arizona |publisher=American Institute of Aeronautics and Astronautics |publication-date=15 April 2007 |id=AIAA Paper 2005-4460}}</ref> americium,<ref name="Ronen2">{{cite journal |last1=Ronen |first1=Yigal |last2=Shwageraus |first2=E. |date=2000 |title=Ultra-thin 241mAm fuel elements in nuclear reactors |journal=Nuclear Instruments and Methods in Physics Research A |volume=455 |issue=2 |pages=442–451 |bibcode=2000NIMPA.455..442R |doi=10.1016/s0168-9002(00)00506-4}}</ref> aerogel core<ref>{{cite web |url=https://www.nasa.gov/directorates/spacetech/niac/2023/Aerogel_Core_Fission_Fragment_Rocket_Engine |title=Aerogel Core Fission Fragment Rocket Engine <!--Unclear who actually wrote this article as there are two names, with no roles labelled. Just citing both as authors -->|first1=Loura |last1=Hall |date=9 January 2023 |first2=Ryan |last2=Weed |publisher=NASA |access-date=21 July 2024}}</ref>
|-
|[[Fission sail]]
|Fission
|Open
|
|
|
|-
|[[Radioisotope rocket]]
|Decay
|Open
|
|
|
|-
|[[Nuclear pulse propulsion|Nuclear fission pulse propulsion]]
|Fission
|Open
|[[Fission bomb]]
|
|{{Flagicon|US}} [[Project Orion (nuclear propulsion)|Project Orion]]
|-
|[[Nuclear pulse propulsion|Nuclear fusion pulse propulsion]]
|Fusion
|Open
|[[Inertial confinement fusion]]
|
|[[Project Daedalus]], [[Project Longshot]]
|-
|[[Fusion rocket|Magnetic fusion rocket]]
|Fusion
|Open
|[[Magnetic confinement fusion]]
|
|[[Direct Fusion Drive]]
|}

==Types==
{{Excerpt|Radioisotope_thermoelectric_generator|Models|only=table}}

===Radioisotope systems===
[[File:SNAP-27 on the Moon.jpg|thumb|SNAP-27 on the Moon]]
For more than fifty years, [[radioisotope thermoelectric generator]]s (RTGs) have been the United States’ main nuclear power source in space. RTGs offer many benefits; they are relatively safe and maintenance-free, are resilient under harsh conditions, and can operate for decades. RTGs are particularly desirable for use in parts of space where solar power is not a viable power source. Dozens of RTGs have been implemented to power 25 different US spacecraft, some of which have been operating for more than 20 years. Over 40 radioisotope thermoelectric generators have been used globally (principally US and USSR) on space missions.<ref name="nasa/doe2010">
{{cite news |last1=Mason|first1=Lee |author2=Sterling Bailey|author3=Ryan Bechtel|author4=John Elliott|author16=Jean-Pierre Fleurial|author5=Mike Houts|author6=Rick Kapernick|author7=Ron Lipinski|author8=Duncan MacPherson|author9=Tom Moreno|author10=Bill Nesmith|author11=Dave Poston|author12=Lou Qualls|author13=Ross Radel|author14=Abraham Weitzberg|author15=Jim Werner |title=Small Fission Power System Feasibility Study — Final Report |url=http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=32899.0;attach=543853 |access-date=3 October 2015 |agency=[[NASA]]/[[US DOE|DOE]] |date=18 November 2010 |quote=''Space Nuclear Power: Since 1961 the U.S. has flown more than 40 Radioisotope Thermoelectric Generators (RTGs) with an essentially perfect operational record. The specifics of these RTGs and the missions they have powered have been thoroughly reviewed in the open literature. The U.S. has flown only one reactor, which is described below. The Soviet Union has flown only 2 RTGs and had shown a preference to use small fission power systems instead of RTGs. The USSR had a more aggressive space fission power program than the U.S. and flew more than 30 reactors. Although these were designed for short lifetime, the program demonstrated the successful use of common designs and technology.''}}</ref>

The [[advanced Stirling radioisotope generator]] (ASRG, a model of [[Stirling radioisotope generator]] (SRG)) produces roughly four times the electric power of an RTG per unit of nuclear fuel, but flight-ready units based on Stirling technology are not expected until 2028.<ref name="Meeting 2015">{{cite web|url=https://prod.nais.nasa.gov/eps/eps_data/165279-OTHER-005-001.pdf |title=Stirling Technical Interchange Meeting |access-date=2016-04-08 |url-status=dead |archive-url=https://web.archive.org/web/20160420084629/https://prod.nais.nasa.gov/eps/eps_data/165279-OTHER-005-001.pdf |archive-date=2016-04-20 }}</ref> NASA plans to utilize two ASRGs to explore [[Titan (moon)|Titan]] in the distant future.{{citation_needed|date=July 2019}}

[[File:ASRG Labeled Cutaway (English).jpg|thumb|Cutaway diagram of the advanced Stirling radioisotope generator.]]

Radioisotope power generators include:
*SNAP-19, SNAP-27 ([[Systems for Nuclear Auxiliary Power]])
*[[MHW-RTG]]
*[[GPHS-RTG]]
*[[MMRTG]]
*[[Advanced Stirling radioisotope generator|ASRG]] (Advanced Stirling radioisotope generator)

[[Radioisotope heater unit]]s (RHUs) are also used on spacecraft to warm scientific instruments to the proper temperature so they operate efficiently. A larger model of RHU called the [[General Purpose Heat Source]] (GPHS) is used  to power RTGs and the ASRG.{{citation needed|date=February 2016}}

Extremely slow-decaying radioisotopes have been proposed for use on interstellar probes with multi-decade lifetimes.<ref name="Ref_t">{{cite web|url=http://interstellarexplorer.jhuapl.edu/index.php |title=Innovative Interstellar Probe |publisher=[[Applied Physics Laboratory|JHU/APL]] |access-date=22 October 2010}}</ref>

As of 2011, another direction for development was an RTG assisted by subcritical nuclear reactions.<ref>{{cite journal|last=Arias|first=F. J.|date=2011|title=Advanced Subcritical Assistance Radioisotope Thermoelectric Generator: An Imperative Solution for the Future of NASA Exploration|url=http://www.jbis.org.uk/paper.php?p=2011.64.314|journal=[[Journal of the British Interplanetary Society]]|volume=64|pages=314–318|bibcode=2011JBIS...64..314A}}</ref>

===Fission systems===
Fission power systems may be utilized to power a spacecraft's heating or propulsion systems. In terms of heating requirements, when spacecraft require more than 100&nbsp;kW for power, fission systems are much more cost effective than RTGs.{{citation needed|date=September 2019}}

In 1965, the [[Federal government of the United States|US]] launched a space reactor, the [[SNAP-10A]], which had been developed by [[Atomics International]], then a division of [[North American Aviation]].<ref name="snap10a">A.A.P.-Reuter (1965-04-05). "Reactor goes into space". The Canberra Times. 39 (11, 122). Australian Capital Territory, Australia. 5 April 1965. p. 1. Via National Library of Australia. Retrieved on 2017-08-12 from https://trove.nla.gov.au/newspaper/article/131765167.</ref>

Over the past few decades, several fission reactors have been proposed, and the [[Soviet Union]] launched 31 [[BES-5]] low power fission reactors in their [[US-A|RORSAT]] satellites utilizing thermoelectric converters between 1967 and 1988.{{citation needed|date=September 2019}}

In the 1960s and 1970s, the Soviet Union developed [[TOPAZ nuclear reactor|TOPAZ reactors]], which utilize thermionic converters instead, although the first test flight was not until 1987.{{citation needed|date=September 2019}}

In 1983, NASA and other US government agencies began development of a next-generation space reactor, the [[SP-100]], contracting with General Electric and others.  In 1994, the SP-100 program was cancelled, largely for political reasons, with the idea of transitioning to the Russian [[TOPAZ nuclear reactor#TOPAZ-II|TOPAZ-II]] reactor system.  Although some TOPAZ-II prototypes were ground-tested, the system was never deployed for US space missions.<ref name="topazii">{{cite book | last = National Research Council | title = Priorities in Space Science Enabled by Nuclear Power and Propulsion | publisher = National Academies | date = 2006 | pages = 114 | isbn = 0-309-10011-9}}</ref>

In 2008, NASA announced plans to utilize a small fission power system on the surface of the Moon and Mars, and began testing "key" technologies for it to come to fruition.<ref>{{cite web|url=http://sservi.nasa.gov/articles/a-lunar-nuclear-reactor/ |title=A Lunar Nuclear Reactor &#124; Solar System Exploration Research Virtual Institute |website=Sservi.nasa.gov |access-date=2016-02-23}}</ref>

Proposed fission power system spacecraft and exploration systems have included [[SP-100]], [[JIMO nuclear electric propulsion]], and [[Fission Surface Power]].<ref name="nasa/doe2010"/>
[[File:SAFE-30 Reactor.png|thumb|[[Safe Affordable Fission Engine|SAFE-30]] small experimental reactor]]
A number of [[micro nuclear reactor]] types have been developed or are in development for space applications:<ref>{{cite web|url=http://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx |title=Nuclear Reactors for Space - World Nuclear Association |website=World-nuclear.org |access-date=2016-02-23}}</ref>
* [[RAPID-L (Nuclear Reactor)|RAPID-L]]
* closed cycle magnetohydrodynamic (CCMHD) power generation system
* [[SP-100]]
* [[Alkali-metal thermal to electric converter|Alkali Metal Thermoelectric Converter (AMTEC)]]
* [[Kilopower]]

Nuclear thermal propulsion systems (NTR) are based on the heating power of a fission reactor, offering a more efficient propulsion system than one powered by chemical reactions. Current research focuses more on nuclear electric systems as the power source for providing thrust to propel spacecraft that are already in space.

Other space fission reactors for powering space vehicles include the [[Safe affordable fission engine|SAFE-400]] reactor and the HOMER-15. In 2020, Roscosmos (the [[Russian Federal Space Agency]]) plans to launch a spacecraft utilizing nuclear-powered propulsion systems (developed at the [[Keldysh Research Center]]), which includes a small gas-cooled fission reactor with 1 MWe.<ref>{{cite news|url=https://www.theregister.co.uk/2011/04/05/russia_nasa_nuclear_spacecraft/|title=Russia, NASA to hold talks on nuclear-powered spacecraft Muscovites have the balls but not the money|last=Page|first=Lewis|date=5 April 2011|publisher=[[The Register]]|access-date=26 December 2013}}</ref><ref>{{cite news|url=http://indrus.in/articles/2012/10/25/breakthrough_in_quest_for_nuclear-powered_spacecraft_18625.html|title=Breakthrough in quest for nuclear-powered spacecraft|date=October 25, 2012|publisher=Rossiiskaya Gazeta|access-date=26 December 2013}}</ref>

[[File:Prometheus1.jpg|thumb|Artists's Conception of Jupiter Icy Moons Orbiter mission for Prometheus, with the reactor on the right, providing power to ion engines and electronics.]]

===Project Prometheus===

In 2002, NASA announced an initiative towards developing nuclear systems, which later came to be known as [[Project Prometheus]]. A major part of the Prometheus Project was to develop the Stirling Radioisotope Generator and the Multi-Mission Thermoelectric Generator, both types of RTGs. The project also aimed to produce a safe and long-lasting space fission reactor system for a spacecraft's power and propulsion, replacing the long-used RTGs. Budget constraints resulted in the effective halting of the project, but Project Prometheus has had success in testing new systems.<ref>{{cite web|title=Nuclear Reactors for Space|url=http://www.world-nuclear.org/info/Non-Power-Nuclear-Applications/Transport/Nuclear-Reactors-for-Space/#.UT1x3VpRgz1|publisher=[[World Nuclear Association]]|access-date=22 November 2013|archive-date=2 February 2016|archive-url=https://web.archive.org/web/20160202224228/http://www.world-nuclear.org/info/non-power-nuclear-applications/transport/nuclear-reactors-for-space/#.UT1x3VpRgz1|url-status=dead}}</ref>  After its creation, scientists successfully tested a [[High Power Electric Propulsion]] (HiPEP) ion engine, which offered substantial advantages in fuel efficiency, thruster lifetime, and thruster efficiency over other power sources.<ref>{{cite web|title=NASA Successfully Tests Ion Engine|url=https://www.sciencedaily.com/releases/2003/11/031121072826.htm|work=ScienceDaily|access-date=22 November 2013}}</ref>

===Fission Surface Power System===
In September 2020, NASA and the [[United States Department of Energy|Department of Energy]] (DOE) issued a formal request for proposals for a lunar nuclear power system, otherwise known as a Fission Surface Power System (FSPS).<ref>{{cite web |url=https://spacenews.com/nasa-to-seek-proposals-for-lunar-nuclear-power-system/ |title=NASA to seek proposals for lunar nuclear power system |website=Space News |date=2 September 2020 }}</ref> The desire for developing these systems is to assist the [[Artemis Project]] in occupying the moon and provide a reliable energy source in areas that have weeks-long lunar night cycles. Furthermore, these systems can be extended to future Mars missions, which further increase design consideration complexity due to atmospheric events, such as dust storms. NASA is collaborating with the DOE Idaho National Laboratory to progress this mission forward.

Phase 1 of the project is focused on the development of different preliminary low enriched uranium material designs to determine the feasibility of the different concepts. The system is expected to be 40&nbsp;kW output at 120 Vdc lasting 10 years, weigh less than 6000&nbsp;kg while fitting on a lander module, and produce less than 5 rem per year at a minimum distance of 1 kilometer.<ref>{{cite web |url=https://ntrs.nasa.gov/api/citations/20230006731/downloads/NETS%202023%20FSP%20Presentation%20FINAL.pdf |title=Overview of NASA Fission Surface Power |date=2023 }}</ref> Three $5 million dollar contracts were awarded in 2022 to [[Lockheed Martin]], [[Westinghouse Electric Corporation]], and IX (joint venture of [[Intuitive Machines]] and [[X-energy]]) to engage in industry developed reactor designs for power conversion, heat rejection, power management, and distribution systems.<ref>{{cite web |url=https://www.nasa.gov/news-release/nasa-announces-artemis-concept-awards-for-nuclear-power-on-moon/ |title=NASA Announces Artemis Concept Awards for Nuclear Power on Moon |website=NASA |date=21 June 2022 }}</ref>

As it currently stands, the initial base location will be located on the southern pole of the moon so there is an almost constant stream of sun light for solar cells to power habitation modules, estimating power limits to be reached at 20&nbsp;kW. The Fission Surface Power System will be at the core of the power flow system and provide the only stable method for power generation without environmental factors. The demo reactor is expected to supply 10&nbsp;kW to the grid, while the full system will provide 40&nbsp;kW. This will enable the use of [[In situ resource utilization]] (ISRU).<ref>{{cite web |url=https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=10115621 |title=Lunar Surface Power Architecture Concepts |website=IEEE |date=2023 }}</ref>

==Visuals==
A gallery of images of space nuclear power systems.
<gallery mode=packed style="text-align:left" heights=200px>
File:Fueling of the MSL MMRTG 001.jpg|Red-hot shell containing plutonium undergoing nuclear decay, inside the [[Mars Science Laboratory]] MMRTG.<ref name="MSLPower">{{cite web |url=http://marsprogram.jpl.nasa.gov/msl/technology/tech_power.html |title=Technologies of Broad Benefit: Power |access-date=2008-09-20 |url-status=dead |archive-url = https://web.archive.org/web/20080614071650/http://marsprogram.jpl.nasa.gov/msl/technology/tech_power.html <!-- Bot retrieved archive --> |archive-date = June 14, 2008}}</ref> MSL was launched in 2011 and landed on Mars in August 2012.
File:Msl-MMRTG.jpg|The MSL MMRTG exterior. The white Aptek 2711 coating reflects sunlight while still transmitting heat to the Martian atmosphere
File:SNAP 10A Space Nuclear Power Plant.jpg| [[SNAP-10A]] Space Nuclear Power Plant, shown here in tests on the Earth, launched into orbit in the 1960s.
Image:Jupiter Icy Moons Orbiter 2.jpg|[[Jupiter Icy Moons Orbiter]]. A long boom holds the reactor at a distance, while a radiation shadow shield protects the [[Spacecraft thermal control#Radiators|radiator]] fins
</gallery>

==See also==
{{portal|Nuclear technology|Spaceflight}}
*[[US-A]]
*[[List of nuclear power systems in space]]
*[[Radioisotope thermoelectric generator#Nuclear power systems in space]]
*[[Austere Human Missions to Mars]]
*[[Nuclear pulse propulsion]]
*[[Nuclear propulsion]]
*[[Nuclear thermal rocket]]
*[[Nuclear electric rocket]]
*[[Batteries in space]]
*[[Solar panels on spacecraft]]

== Notes ==
{{reflist|group=note}}

==References==
{{Reflist|30em}}

==External links==
*[https://www.youtube.com/watch?v=kIoxfHtplWY KRUSTY - Kilopower Reactor Using Stirling Technology]
*[https://archive.today/20160531024842/http://naca.larc.nasa.gov/search.jsp?R=20120000789&qs=N=4294966387+4294957355 Small Fission Power System Feasibility Study] 
*[https://web.archive.org/web/20120217193720/http://www.ne.doe.gov/pdfFiles/NPSPACE.PDF Nuclear Power in Space - Office of Nuclear Energy - U.S. Department of Energy](.pdf)
*[http://adsabs.harvard.edu/abs/2002AIPC..608..578P SAFE-400 paper] (fission reactor)
*[https://web.archive.org/web/20140211151051/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/10669/1/02-2767.pdf Design Concept for a Nuclear Reactor-Powered Mars Rover]
*[http://spacenuke.blogspot.com/ David Poston, "Space Nuclear Power: Fission Reactors"]
*[http://local.ans.org/trinity/files/mcclure-130920.pdf Design and Testing of Small Nuclear] (.pdf file)
*[https://web.archive.org/web/20120807005925/http://solarsystem.nasa.gov/rps/rtg.cfm Overview of NASA and nuclear power in space]
*[https://www.scientificamerican.com/article/nasa-seeks-nuclear-power-for-mars/ NASA Seeks Nuclear Power for Mars] (December 2017)

{{Inspace}}

[[Category:Nuclear power in space| ]]
[[Category:Nuclear power|Space]]
[[Category:Space technology]]
[[Category:Nuclear spacecraft propulsion]]