Space Reactor Freedom (SR-1) Begins Development, Targeting 2028 Launch

Recently, NASA has announced a new Mars mission, comprised of three Ingenuity-class Mars helicopters, being carried on the largest nuclear fission reactor on a spacecraft ever. This craft will be called the Space Reactor Freedom, also known as SR-1. It will use a 12 kilowatt hall thruster, a type of ion engine, to propel itself to Mars.

Nuclear fission in space has been demonstrated before, by both the United States and previously, the Soviet Union. But, it has comprised of short term scientific expirements, rather than full missions. But, this is coming to a close. NASA is currently developing this spacecraft, the SR-1, to meet the ever present need of power in space. With even a small nuclear reactor, placed aboard a spacecraft with electric propulsion, the gains in efficiency can go above 5x compared to standard chemical rocketry.

In comparison with the two current ways of powering spacecraft long-term, solar panels, and radioisotope thermoelectric generators (RTGs), nuclear power can generate more than both. Solar panels work via the photovoltaic effect, where sunlight is turned into a flow of electrons (electricity). Radioisotope thermoelectric generators use the warm decay of radioactive isotopes to generate electricity via the Seebeck Effect, where, in certain materials, electrons can flow from the hot areas to the cooler areas, generating electric current (power).

While RTGs and fission reactors sound similar, they use completely different nuclear processes for energy, and RTGs are passive while fission reactors are active mechanisms. Plutonium-238, the most common used isotope in RTGs, undergoes alpha decay, where the Plutonium nucleus splits into a Uranium-234 nucleus and an alpha particle (helium-4 nucleus, no electrons).