NASA hopes to send a new spacecraft to Mars by 2028—a mission for which nuclear power may be more viable than traditional propulsion.

NASA will pay Kratos Defense & Security Solutions $33.6 million to help develop its Space Reactor-1 (SR-1) Freedom Spacecraft, which is intended to become the first American interplanetary vehicle powered by an onboard nuclear fission reactor.

NASA hopes to launch the spacecraft in 2028 for travel to Mars. In the meantime, Kratos will develop the system responsible for converting nuclear reactor heat into usable electrical power.

About the SR-1 Spacecraft

The SR-1 Freedom Spacecraft is a planned NASA spacecraft that is expected to demonstrate the viability of nuclear fission power and nuclear-electric propulsion beyond Earth’s orbit. The mission’s objectives will include traveling from Earth toward Mars—at least for starters—while demonstrating a space-based nuclear reactor, testing nuclear electric propulsion technology, and delivering a scientific payload called SkyFall.

Until now, conventional spacecraft have either been powered by solar panels (which are far more efficient in space, given the absence of an atmosphere blocking the sun) or by chemical propulsion. The SR-1, however, will have an onboard nuclear reactor, hopefully demonstrating that nuclear systems can reliably provide power for propulsion and other vital operations during long-distance missions between planets. According to Kratos, the program should reduce technical risks while developing the industrial capabilities necessary for nuclear-powered spacecraft operations in the near future.

Kratos will operate as a subcontractor to Sierra Lobo under NASA’s SpaceDOC III contract. Its assignment is to design, manufacture, and deliver a closed Brayton cycle power conversion system, effectively converting the thermal energy from the nuclear reactor into mechanical energy and thereafter into electricity. In simple terms, the space reactor will work the same way a commercial nuclear reactor works on Earth: the reactor generates heat through nuclear fission, a gas absorbs the thermal energy, the heated gas drives a turbine, which in turn drives an electrical generator, before the gas is cooled and recirculated through the closed system. The result is electricity that is used to power the spacecraft systems and electric propulsion thrusters—and because the system is self-contained, it does not release nuclear radiation into the surrounding environment.

Of course, because this technology is being used in space, it needs to be compact, lightweight, and capable of operating under extreme conditions. Kratos has yet to announce its design for the reactor.

How Would a Nuclear-Powered Rocket Actually Work?

Nuclear electric propulsion (NEP) works by using a reactor to generate electricity, which in turn powers the vehicle’s means of propulsion. This is roughly analogous to the propulsion of an aircraft carrier or nuclear submarine, in which nuclear-generated electricity powers a turbine. In space, of course, the process is harder, as there is nothing for a turbine to push against; instead, the electricity is used to power electric thrusters, which accelerate charged particles to produce thrust.

Unlike chemical rockets, which generate enormous thrust over relatively short time periods, electric propulsion produces a lower but sustained thrust. There are advantages with electric propulsion, like high propellant efficiency, long-duration operation, reduced propellant requirements, and greater payload flexibility. The downside is that electric propulsion provides relatively little instantaneous thrust, making it difficult to change direction quickly.

The program will not be the first time NASA has pursued nuclear power in space. In 1965, NASA launched the SNAP-10A nuclear reactor into Earth orbit, although it never traveled beyond orbit. In 2020, NASA sent the Perseverance rover to Mars, powered by a “radioisotope thermoelectric generator,” a type of nuclear battery powered by decaying radioactive isotopes converted into heat.

The hope today is that nuclear electric propulsion can support future missions where solar power becomes less practical, or where a spacecraft needs more electrical power. Potential examples of such a mission include cargo transportation to Mars, long-duration robotic exploration, or a mission involving power-intensive scientific instruments.

SR-1 Freedom could mark an important step towards functional nuclear power in space. The Kratos contract seeks to advance a critical component of the spacecraft’s electrical system. The question now is whether the ambitions of the program and the contract can be fulfilled before the fast-approaching 2028 launch.

About the Author: Harrison Kass

Harrison Kass is a writer and attorney focused on national security, technology, and political culture. His work has appeared in Tablet, City Journal, The Hill, The Spectator, and The Cipher Brief. He holds a JD from the University of Oregon and a master’s in Global & Joint Program Studies from NYU. More at harrisonkass.com.

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