The Study concludes that there is a continuing demand for radioisotope power systems, which have been used in deep space exploration for decades, but that there is no imminent requirement for a new fission reactor program.
The 177-page Study, prepared for NASA by Johns Hopkins University Applied Physics Laboratory, had been completed several months ago but was withheld from public release due to unspecified “security concerns,” according to Space News. Those concerns may have involved the discussion of the proposed use of highly enriched uranium as fuel for a space reactor, or the handling of plutonium-238 for radioisotope power sources.
Nuclear power can be enabling for a variety of space missions because it offers high power density in compact, rugged form. Radioisotope power sources (in which the natural heat of decay is converted into electricity) have contributed to some of the U.S. space program’s greatest achievements, including the Voyager I and II probes to the outer solar system and beyond. But development of nuclear reactor technology for use in space has been dogged by a repeated series of false starts in which anticipated mission requirements failed to materialize.
“The United States has spent billions of dollars on space reactor programs, which have resulted in only one flight of an FPS [fission power source],” the new NASA report noted. That was the 1965 launch of the SNAP 10-A reactor on the SNAPSHOT mission. It had an electrical failure after a month’s operation and “it remains in a 1300-km altitude, ‘nuclear-safe’ orbit, although debris-shedding events of some level may have occurred,” the report said.
The development and use of space nuclear power raises potential environmental safety and public health issues. As a result, the NASA report said, “it may be prudent to build in more time in the development schedule for the first launch of a new space reactor. Public interest would likely be large, and it is possible that opposition could be substantial.”
In any case, specific presidential approval is required for the launch of a nuclear power source into space, pursuant to Presidential Directive 25 of 1977.
“For any U.S. space mission involving the use of RPS [radioisotope power sources], radioisotope heating units, nuclear reactors, or a major nuclear source, launch approval must be obtained from the Office of the President,” the report noted.