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59-619: Kilopower is an experimental U.S. project to make new nuclear reactors for space travel . The project started in October 2015, led by NASA and the DoE ’s National Nuclear Security Administration (NNSA). As of 2017, the Kilopower reactors were intended to come in four sizes, able to produce from one to ten kilowatts of electrical power (1–10 kW e ) continuously for twelve to fifteen years. The fission reactor uses uranium-235 to generate heat that

118-558: 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 . 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

177-484: A nuclear meltdown . The primary method is passive cooling, which requires no mechanical mechanisms to circulate coolant. The reactor design is self-regulating through design geometry that creates a negative temperature reactivity coefficient . In effect this means that as the power demand increases the temperature of the reactor drops. This causes it to shrink, preventing neutrons from leaking out. This in turn causes reactivity to increase and power output to increase to meet

236-400: A 40 kW e reactor would be sufficient to support a crew of between 4 and 6 astronauts. The reactor is fueled by an alloy of 93% uranium-235 and 7% molybdenum . The core of the reactor is a solid cast alloy structure surrounded by a beryllium oxide reflector, which prevents neutrons from escaping the reactor core and allows the chain reaction to continue. The reflector also reduces

295-447: A linear electric generator . The melting point of sodium is 98 °C (208 °F), which means that liquid sodium can flow freely at high temperatures between about 400 and 700 °C (750 and 1,300 °F). Nuclear fission cores typically operate at about 600 °C (1,100 °F). The reactor is designed to be intrinsically safe in a wide range of environments and scenarios. Several feedback mechanisms are employed to mitigate

354-399: A mass of 1500 kg in total (with a 226 kg core) and contain 43.7 kg of U . Nuclear reaction control is provided by a single rod of boron carbide , which is a neutron absorber . The reactor is intended to be launched cold, preventing the formation of highly radioactive fission products . Once the reactor reaches its destination, the neutron absorbing boron rod

413-431: 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. NASA plans to utilize two ASRGs to explore Titan in the distant future. Radioisotope power generators include: Radioisotope heater units (RHUs) are also used on spacecraft to warm scientific instruments to

472-481: A power-distance drop-off of P ∝ R − 4 {\displaystyle P\propto R^{-4}} , comparatively low Earth orbits are desirable. The Soviet Union did not launch interplanetary missions beyond Mars, and generally developed few RTGs. American RTGs in the 1970s supplied power in the 100 W range. For the RORSAT military radar satellites (1967–1988), fission reactors, especially

531-592: 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. 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. A gallery of images of space nuclear power systems. Flattop (critical assembly) Flattop

590-726: A second phase, by early 2022, they would select one company to develop a 10-kilowatt fission power system to be placed on the Moon in 2027. 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

649-470: A sensitive issue by states. 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. For example, all Radioisotope Power Systems (RPS) used in space missions have utilized Pu-238. Plutonium-238

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708-522: A spacecraft utilizing nuclear-powered propulsion systems (developed at the Keldysh Research Center ), which includes a small gas-cooled fission reactor with 1 MWe. In September 2020, NASA and the Department of Energy (DOE) issued a formal request for proposals for a lunar nuclear power system, in which several awards would be granted to preliminary designs completed by the end of 2021, while in

767-527: 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. In 1965, the US launched a space reactor, the SNAP-10A , which had been developed by Atomics International , then a division of North American Aviation . Over the past few decades, several fission reactors have been proposed, and

826-446: Is a benchmark critical assembly that is used to study the nuclear characteristics of uranium-233 , uranium-235 , and plutonium-239 in spherical geometries surrounded by a relatively thick natural uranium neutron reflector . Flattop assemblies are used to measure neutron activation and reactivity coefficients. Since the neutron energies gradually decrease in the reflector, experiments may be run in various energy spectra based on

885-479: 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

944-537: Is carried to the Stirling converters with passive sodium heat pipes . In 2018, positive test results for the Kilopower Reactor Using Stirling Technology ( KRUSTY ) demonstration reactor were announced. Potential applications include nuclear electric propulsion and a steady electricity supply for crewed or robotic space missions that require large amounts of power, especially where sunlight

1003-571: Is exactly the same material as the regular high-enriched uranium (HEU) core with the only difference being the level of uranium enrichment . The prototype Kilopower uses a solid, cast uranium-235 reactor core , about the size of a paper towel roll. Reactor heat is transferred via passive sodium heat pipes , with the heat being converted to electricity by Stirling engines . Testing to gain technology readiness level (TRL) 5 started in November 2017 and continued into 2018. The testing of KRUSTY represents

1062-461: Is highly advantageous for outer solar system exploration i.e. Jupiter and beyond. All spacecraft leaving the Solar System , i.e. Pioneer 10 and 11 , Voyager 1 and 2 , and New Horizons use NASA RTGs, as did the outer planet missions of Galileo , Cassini , and Ulysses . However, in part, due to the global shortage of plutonium-238 , and advances in solar efficiency,

1121-477: Is limited or not available. NASA has also studied the Kilopower reactor as the power supply for crewed Mars missions. During those missions, the reactor would provide power for the machinery necessary to separate and cryogenically store oxygen from the Martian atmosphere for ascent vehicle propellants. Once humans arrive the reactor would power their life-support systems and other requirements. NASA studies have shown that

1180-583: Is located at the Nevada National Security Site . However, NCERC continues to be operated by the Los Alamos National Laboratory. The core capabilities at NCERC include Flattop along with three other critical assemblies, Comet, Planet, and Godiva -IV and a significant inventory of nuclear material items available for experimental use. NCERC critical operations commenced in 2011 and continue to be operational today. In 2012, Flattop

1239-725: Is no longer usable because of its high gamma-ray activity. The experiment was originally located at the Los Alamos National Laboratory Critical Experiments Facility (LACEF) located at the Los Alamos Pajarito Site , otherwise known as Technical Area 18. In 2005 the Pajarito Site started to shut down and nuclear material was moved to the National Criticality Experiments Research Center (NCERC) which

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1298-487: Is removed to allow the nuclear chain reaction to start. Once the reaction is initiated, decay of a series of fission products cannot be stopped completely. However, the depth of control rod insertion provides a mechanism to adjust the rate of the uranium fission, allowing the heat output to match the load. Passive heat pipes filled with liquid sodium transfer the reactor core heat to one or more free-piston Stirling engines , which produce reciprocating motion to drive

1357-699: The BES-5 , were developed to supply an average of 2 kW to the radar. At altitudes averaging 255.3 km, they would have rapidly decayed if they had used a large solar array instead. The later United States Lacrosse/Onyx radar satellite program, beginning launches in 1988, operated at altitudes of 420–718 km. To power radar at this range, a solar array reportedly 45 m in length was operated, speculated to supply 10–20 kW. The following technologies have been proposed and in some cases ground or space-tested for propulsion via nuclear energy. process For more than fifty years, radioisotope thermoelectric generators (RTGs) have been

1416-532: 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. The more powerful TOPAZ-II reactor produced 10 kilowatts of electricity. Examples of concepts that use nuclear power for space propulsion systems include

1475-561: 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. 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 . As active electromagnetic detectors including radar observe

1534-631: The SNAP-27 RTG exploded and crashed into the South Pacific Ocean, with no leakage of nuclear fuel. This is the only intact flown nuclear system that remains on Earth without recovery. 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

1593-562: 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-II reactor system. Although some TOPAZ-II prototypes were ground-tested, the system was never deployed for US space missions. In 2008, NASA announced plans to utilize a small fission power system on the surface of

1652-479: The Soviet Union launched 31 BES-5 low power fission reactors in their RORSAT satellites utilizing thermoelectric converters between 1967 and 1988. In the 1960s and 1970s, the Soviet Union developed TOPAZ reactors , which utilize thermionic converters instead, although the first test flight was not until 1987. In 1983, NASA and other US government agencies began development of a next-generation space reactor,

1711-563: The 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 / ISAS ' 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. The presence of space nuclear sources and

1770-600: 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 and 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

1829-563: The nuclear electric rocket (nuclear powered ion thruster (s)), the radioisotope rocket , and radioisotope electric propulsion (REP). 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 . After the ban of nuclear weapons in space by the Outer Space Treaty in 1967, nuclear power has been discussed at least since 1972 as

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1888-884: The Canadian Northwest Territories. COSMOS 954 became the first example for global emergency preparedness and response arrangements for satellites carrying nuclear power sources. The majority of nuclear power systems launched into space remain in graveyard orbits around Earth. Between 1980 and 1989, the BES-5 and 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 km altitude orbits, comprising 10% of

1947-408: The Moon and Mars, and began testing "key" technologies for it to come to fruition. Proposed fission power system spacecraft and exploration systems have included SP-100 , JIMO nuclear electric propulsion , and Fission Surface Power . A number of micro nuclear reactor types have been developed or are in development for space applications: Nuclear thermal propulsion systems (NTR) are based on

2006-661: 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. The advanced Stirling radioisotope generator (ASRG,

2065-605: The demand. This also works in reverse at times of lower power demand. The development of Kilopower began with an experiment called DUFF or Demonstration Using Flattop Fissions , which was tested in September 2012 using the existing Flattop assembly as a nuclear heat source. When DUFF was tested at the Device Assembly Facility at the Nevada Test Site , it became the first Stirling engine powered by fission energy and

2124-456: The emissions of gamma radiation that could impair on-board electronics. A uranium core has the benefit of avoiding uncertainty in the supply of other radioisotopes, such as plutonium-238 , that are used in RTGs . The prototype KRUSTY 1 kW e Kilopower reactor weighs 134 kg and contains 28 kg of U . The space-rated 10 kW e Kilopower for Mars is expected to have

2183-462: The environment, posing hazards to both the environment and human health. Pu-238 primarily accumulates in the lungs, liver, and bones through inhalation of powdered form, thereby posing risks to human health. There have been several environmental accidents related to space nuclear power in history. In 1964, a Thor-Ablestar rocket carrying the Transit 5BN-3 satellite failed to reach orbit, destroying

2242-417: 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. At the global level, following the 1978 COSMOS 954 incident,

2301-640: The existing infrastructure and regulatory environment". In 2017, the KRUSTY test reactor was completed. KRUSTY is designed to produce up to 1 kilowatt of electric power and is about 6.5 feet tall (1.9 meters). The goal of the test reactor is to closely match the operational parameters that would be required in NASA deep space missions. The first tests used a depleted uranium core manufactured by Y-12 National Security Complex in Oak Ridge , Tennessee. The depleted uranium core

2360-474: The first time the United States has conducted ground tests on any space reactor since the SNAP-10A experimental reactor was tested and eventually flown in 1965. During November 2017 through March 2018, testing of KRUSTY was conducted at Nevada National Security Site . The tests included thermal, materials, and component validation, and culminated in a successful fission trial at full-power. Various faults in

2419-544: The first use of a heat pipe to transport heat from a reactor to a power conversion system. According to David Poston, the leader of the Compact Fission Reactor Design Team, and Patrick McClure, the manager for small nuclear reactor projects at Los Alamos National Laboratory , the DUFF experiment showed that "for low-power reactor systems, nuclear testing can be accomplished with reasonable cost and schedule within

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2478-500: The heat-removal system. A Scram test concluded the experiment. The test was considered to be a highly successful demonstration. Nuclear reactor for space 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 (DUFF) test of

2537-621: 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-400 reactor and the HOMER-15. In 2020, Roscosmos (the Russian Federal Space Agency ) plans to launch

2596-626: 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." These principles primarily address safety assessment, international information exchange and dialogue, responsibility, and compensation. It stipulates that

2655-484: The likelihood and mitigate the consequences of potential accidents. 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. 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

2714-535: The location in which they are placed. Flattop is a natural-uranium-reflected, benchmarked, fixed-geometry critical assembly machine that can accommodate plutonium or uranium cores. The fast neutron spectrum is used to provide benchmarked neutronic measurements in spherical geometry with different fissile driver materials. Key missions for Flattop include fundamental reactor physics studies, sample irradiation for radiochemical research, actinide minimum critical mass studies, detector calibration, and training. The U-233 core

2773-482: The magnetosphere's flux tubes , which carry them through a range of orbital altitudes, where the positrons can annihilate with the structure of other satellites, again producing gamma rays: e + + e − ⟶ γ   + γ {\displaystyle e^{+}+e^{-}\longrightarrow \gamma \ +\gamma } These gamma rays can interfere with satellite instruments. This most notably occurred in 1987, when

2832-460: The more recent Jupiter missions of Juno , Jupiter Icy Moons Explorer , and Europa Clipper , as well as the Jupiter trojan asteroid mission of Lucy , all opted for large solar arrays despite a relative 4% solar flux at Jupiter's orbit of 5.2 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

2891-552: The ownership, use, and production of nuclear materials and facilities. The Department of Energy is bound by the National Environmental Policy Act (NEPA) to consider the environmental impact of nuclear material handling, transportation, and storage. NASA, the Department of Energy, and other federal and local authorities develop comprehensive emergency plans for each launch, including timely public communication. In

2950-536: 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. 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 NRC oversee

3009-419: 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

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3068-756: The principles should be revisited by the Committee on the Peaceful Uses of Outer Space no later than two years after adoption. 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. The "Safety Framework" asserts that each nation bears responsibility for

3127-547: 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. Extremely slow-decaying radioisotopes have been proposed for use on interstellar probes with multi-decade lifetimes. As of 2011, another direction for development was an RTG assisted by subcritical nuclear reactions. Fission power systems may be utilized to power

3186-544: 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. Nuclear power systems function independently of sunlight, which

3245-518: 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

3304-477: 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 kilocuries 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. In May 1968,

3363-1358: The space debris in that size range. Orbital fission reactors are a source of significant interference for orbital 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: 0 1 n   +   92 235 U ⟶   56 141 Ba   +   36 92 Kr   +   3   0 1 n   + γ {\displaystyle {\begin{array}{r}^{1}_{0}{\text{n}}\ +\ _{92}^{235}{\text{U}}\longrightarrow \ _{56}^{141}{\text{Ba}}\ +\ _{36}^{92}{\text{Kr}}\ +\ 3\ _{0}^{1}{\text{n}}\ +\gamma \end{array}}} Pair production occurs as these gamma rays interact with reactor or adjacent material, ejecting electrons and positrons into space: γ + Z ⟶   e + + e − + Z   {\displaystyle \gamma +{\text{Z}}\longrightarrow \ e^{+}+e^{-}+{\text{Z}}\ } These electrons and positrons then become trapped in

3422-496: The supporting equipment were simulated to ensure the reactor could respond safely. The KRUSTY reactor was run at full power on March 20, 2018 during a 28-hour test using a 28 kg uranium-235 reactor core. It reached 850 °C (1,560 °F) and generated about 5.5 kW of fission power. The test evaluated failure scenarios including shutting down the Stirling engines, adjusting the control rod, thermal cycling, and disabling

3481-528: Was used for key demonstration of the use of nuclear power for space applications. The Demonstration Using Flattop Fission, or DUFF, test was planned by Los Alamos National Laboratory to use Flattop as a nuclear heat source. A team from the NASA Glenn Research Center in partnership with the LANL reactor design team designed, built, and tested a heat pipe and power conversion system to couple to Flattop with

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