Nuclear power in space

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The KIWI A prime nuclear thermal rocket engine
Mars Curiosity rover powered by a RTG on Mars

Nuclear power in space is the use of nuclear power in outer space, typically either small fission systems or radioactive decay for electricity or heat. Another use is for scientific observation, as in a Mössbauer spectrometer. One common type is a radioisotope thermoelectric generator, which has been used on many space probes and on manned lunar missions, and another is small fission reactors for Earth observation satellites such as the TOPAZ nuclear reactor.[1] A radioisotope heater unit provides heat from radioactive decay of a material and can potentially produce heat for decades.[2]

Russia has sent about 40 reactors into space and its TOPAZ-II reactor can produce 10 kilowatts.[3] The Romashka reactor family uses uranium and direct thermoelectric conversion to electricity, rather than using a heated fluid to drive a turbine.[4] The United States tested a nuclear reactor in space for 43 days in 1965.[3] While not yet tested in space, the test of the Demonstration Using Flattop Fission (DUFF) on September 13, 2012 was the first test of a nuclear reactor power system for space since then.[5]

Examples of nuclear power for space propulsion systems include nuclear electric rocket (nuclear electric propulsion), radioisotope rocket, and radioisotope electric propulsion (REP).[6] One of the more explored is the nuclear thermal rocket, which was tested in the NERVA program. See also Category:Nuclear spacecraft propulsion (category link). Nuclear pulse propulsion was the subject of Project Orion (nuclear propulsion)


Both the Viking 1 and Viking 2 landers used RTGs for power on the surface of Mars—they were launched (a Viking launch vehicle pictured) and landed on Mars in the late 1970s

While solar power is much more commonly used, nuclear power offers great advantages in many areas. Solar cells, although efficient, can only supply energy to spacecraft in orbits where the solar flux is sufficiently high, such as low Earth orbit and interplanetary destinations close enough to the Sun. Unlike solar cells, nuclear power systems function independently of sunlight, which is necessary for deep space exploration. Nuclear reactors are especially beneficial in space because of their lower weight-to-capacity ratio than solar cells. Therefore, nuclear power systems take up much less space than solar power systems. Compact spacecraft are easier to orient and direct in space when precision is needed. Estimates of nuclear power, which can power both life support and propulsion systems, suggest that use of these systems can effectively reduce both cost and flight time.[7]

Selected applications and/or technologies for space include


Radioisotope systems[edit]

SNAP-27 on the Moon

For more than fifty years, radioisotope thermoelectric generators (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.[8]

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 it is not yet ready to be implemented on an actual mission. NASA plans to utilize two ASRGs to explore Titan in the distant future.

Cutaway diagram of the advanced Stirling radioisotope generator.

Radioisotope power generators include:

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

Extremely slow-decaying radioisotopes have been proposed for use on realistic interstellar probes with multi-decade lifetimes.[9]

Another direction for development is an RTG assisted by subcritical reactions.[10]

Fission systems[edit]

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 kW for power, fission systems are much more cost effective than RTGs. Over the past few decades, several fission reactors have been proposed, but these fission systems haven’t been utilized in US space projects as prominently as radioisotope systems have. The Soviet Union, however, launched 31 BES-5 low power fission reactors in their RORSAT satellites utilizing thermoelectric converters between 1967 and 1988. Shortly after, the Soviet Union developed TOPAZ reactors, which utilize thermionic converters instead. In 2008, NASA announced plans to utilize a small fission power system to be used on the surface of the moon and Mars, and began testing "key" technologies for it to come to fruition.[11]

Nuclear thermal propulsion systems (NTR) are based on the heating power of a fission reactor, offering a more efficient propulsion system for thrust in launches and landings 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.

SAFE-30 small experimental reactor circa 2002

Other space fission reactors for powering space vehicles include the 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.[12][13]

As of 2010, more than 30 small fission power system nuclear reactors have been sent into space in the Soviet RORSAT satellites, with only one—SNAP-10A—by the US.

Proposed fission power system spacecraft and exploration systems have included SP-100, JIMO nuclear electric propulsion, and Fission Surface Power.[8]

A number of Micro nuclear reactor types have been developed or are in development for space applications:[14]

Project Prometheus[edit]

Artists's Conception of Jupiter Icy Moons Orbiter which was mission for Prometheus. It was powered by a small fission reactor, which provided electrical power to ion engines and electronics. The long boom is used to create distance between the reactor and the rest of the space craft, on it are fins that radiate waste heat into space

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.[15] 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.[16]


Examples of nuclear powered spacecraft:

Name and/or model Fate/Location
Selected examples of nuclear power systems in space[17]
SNAP-10A Earth orbit (900+ km altitude)
Cosmos 469 BES-5 Buk
Cosmos 516 High orbited 1972
Cosmos 626 Earth orbit
Cosmos 954 Earth re-entry 1978 (over Canada)
Cosmos 1176 11788/11971 Earth orbit 870–970 km
Cosmos 1402 Earth re-entry 1983 (South Atlantic)
Cosmos 1607 High orbited 1985
Cosmos 1670 High orbited 1985
Cosmos 1677 High orbited 1985
Cosmos 1682 High orbited 1986
Cosmos 1736 High orbited 1986
Cosmos 1771 High orbited 1986
Cosmos 1818 TEU-5 Topol Earth orbit[18]
Cosmos 1860
Cosmos 1867 TEU-5 Topol
Cosmos 1900 High orbited 1987
Cosmos 1932 Earth orbit 800–900 km

See also Radioisotope thermoelectric generator#Nuclear power systems in space


Red-hot shell containing plutonium undergoing nuclear decay, inside the Mars Science Laboratory MMRTG.[19] MSL was launched in 2011 and landed on Mars in August 2012.
The MSL MMRTG exterior
SNAP-10A Space Nuclear Power Plant, shown here in tests on the Earth, launched into orbit in the 1960s.

See also[edit]


  1. ^ Hyder, Anthony K.; R. L. Wiley; G. Halpert; S. Sabripour; D. J. Flood (2000). Spacecraft Power Technologies. Imperial College Press. p. 256. ISBN 1-86094-117-6.
  2. ^ "Department of Energy Facts: Radioisotope Heater Units" (PDF). U.S. Department of Energy, Office of Space and Defense Power Systems. December 1998. Archived from the original (PDF) on May 27, 2010. Retrieved March 24, 2010.
  3. ^ a b "Nuclear Power In Space". Retrieved 2016-02-23.
  4. ^ Ponomarev-Stepnoi, N. N.; Kukharkin, N. E.; Usov, V. A. (March 2000). ""Romashka" reactor-converter". Atomic Energy. New York: Springer. 88 (3): 178–183. doi:10.1007/BF02673156. ISSN 1063-4258. Retrieved 2009-01-06.
  5. ^ "NASA - Researchers Test Novel Power System for Space Travel - Joint NASA and DOE team demonstrates simple, robust fission reactor prototype". 2012-11-26. Retrieved 2016-02-23.
  6. ^ "Radioisotope Electric Propulsion : Enabling the Decadal Survey Science Goals for Primitive Bodies" (PDF). Retrieved 2016-02-23.
  7. ^ Zaitsev, Yury. "Nuclear Power In Space". Spacedaily. Retrieved 22 November 2013.
  8. ^ a b Mason, Lee; Sterling Bailey; Ryan Bechtel; John Elliott; Mike Houts; Rick Kapernick; Ron Lipinski; Duncan MacPherson; Tom Moreno; Bill Nesmith; Dave Poston; Lou Qualls; Ross Radel; Abraham Weitzberg; Jim Werner; Jean-Pierre Fleurial (18 November 2010). "Small Fission Power System Feasibility Study — Final Report". NASA/DOE. Retrieved 3 October 2015. 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.
  9. ^ "Innovative Interstellar Probe". JHU/APL. Retrieved 22 October 2010.
  10. ^ Arias, F. J. (2011). "Advanced Subcritical Assistance Radioisotope Thermoelectric Generator: An Imperative Solution for the Future of NASA Exploration". Journal of the British Interplanetary Society. 64: 314–318. Bibcode:2011JBIS...64..314A.
  11. ^ "A Lunar Nuclear Reactor | Solar System Exploration Research Virtual Institute". Retrieved 2016-02-23.
  12. ^ Page, Lewis (5 April 2011). "Russia, NASA to hold talks on nuclear-powered spacecraft Muscovites have the balls but not the money". The Register. Retrieved 26 December 2013.
  13. ^ "Breakthrough in quest for nuclear-powered spacecraft". Rossiiskaya Gazeta. October 25, 2012. Retrieved 26 December 2013.
  14. ^ "Nuclear Reactors for Space - World Nuclear Association". Retrieved 2016-02-23.
  15. ^ "Nuclear Reactors for Space". World Nuclear Association. Retrieved 22 November 2013.
  16. ^ "NASA Successfully Tests Ion Engine". ScienceDaily. Retrieved 22 November 2013.
  17. ^ Sven Grahn. "The US-A program (Radar Ocean Reconnaissance Satellites)". Retrieved 2016-02-23.
  18. ^ "Old Russian Nuclear Satellite Returns". Retrieved 2016-02-23.
  19. ^ "Technologies of Broad Benefit: Power". Archived from the original on June 14, 2008. Retrieved 2008-09-20.

External links[edit]