Nuclear power in space

[1] 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.

[10] Pu-238 primarily accumulates in the lungs, liver, and bones through inhalation of powdered form, thereby posing risks to human health.

[13] 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.

[citation needed] In early 1978, the Soviet spacecraft Kosmos 954, powered by a 45-kilogram highly enriched uranium reactor, went into an uncontrolled descent.

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.

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

[18] For instance, in the United States, safety considerations are integrated into every stage of the design, testing, manufacturing, and operation of space nuclear systems.

[9][19] 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.

[20] 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.

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.

[23] 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.

[22] 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.

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, 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.

[35] process For more than fifty years, radioisotope thermoelectric generators (RTGs) have been the United States’ main nuclear power source in space.

A larger model of RHU called the General Purpose Heat Source (GPHS) is used to power RTGs and the ASRG.

[citation needed] 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.

[citation needed] 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.

[citation needed] 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.

[49] 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.

Current research focuses more on nuclear electric systems as the power source for providing thrust to propel spacecraft that are already in space.

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.

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.