page_title: Nuclear power in space
section_title: Benefits
hierarchical_section_title: Nuclear power in space / Benefits
caption_attribution_description: English: The Titan booster is a two-stage liquid-fueled rocket, with two additional large, solid-propellant rockets attached. It is a member of the Titan family that was used in NASA's Gemini program. The Centaur is a liquid oxygen- liquid hydrogen, high- energy upper stage used on Surveyor flights to the Moon and on Mariner flights to Mars. At liftoff, the solid rockets provide 9.61 million newtons (2.16 million pounds) of thrust. When the solids burn out, the first stage of the Titan booster ignites, and followed by the second-stage ignition as the first stage shuts down. The Centaur ignites on second stage shutdown to inject the spacecraft into orbit. Then after a 30-minute coast around the Earth into position for re-start, the Centaur re-ignites to propel Viking on its Mars trajectory. Once this maneuver is completed the spacecraft separates from the Centaur, which subsequently is deflected away from the flight path to prevent its impact on the surface of Mars. Shortly after separating from the Centaur, the orbiter portion of the combined orbiter-lander spacecraft orients and stabilizes the spacecraft by using the Sun and a very bright star in the southern sky, Canopus, for celestial reference.
context_page_description: 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. 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. 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.
  The United States tested the SNAP-10A nuclear reactor in space for 43 days in 1965, 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 test of the Kilopower reactor.
  After a ground-based test of the experimental 1965 Romashka reactor, which used uranium and direct thermoelectric conversion to electricity, the USSR sent about 40 nuclear-electric satellites into space, mostly powered by the BES-5 reactor.
context_section_description: While solar power is much more commonly used, nuclear power can offer advantages in some 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-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. 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.
  Selected applications and/or technologies for space include:
  Radioisotope thermoelectric generator
  Radioisotope heater unit
  Radioisotope piezoelectric generator
  Radioisotope rocket
  Nuclear thermal rocket
  Nuclear pulse propulsion
  Nuclear electric rocket
caption: Both the Viking 1 and Viking 2 landers used RTGs for power on the surface of Mars. (Viking launch vehicle pictured)
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