NASA's plan to fly a nuclear reactor to Mars has taken another step forward. In an update published October 20, the agency said it and its partners have agreed to key contract actions for Space Reactor-1 (SR-1) Freedom, which NASA says will be the first fission-powered spacecraft to travel beyond Earth's orbit.
The update focuses on the spacecraft's most important piece: the nuclear power module.
Who's building what
According to NASA, Sierra Lobo Inc. will provide the power module's closed Brayton cycle power conversion system, which turns heat from the fission reactor into the electricity needed for SR-1 Freedom's nuclear electric propulsion demonstration. The work falls under the Space Flight Systems Development and Operations Contract III, awarded in 2024, which supports spaceflight hardware work at NASA's Glenn Research Center in Cleveland.
The reactor itself is being designed and developed by the Department of Energy's Idaho National Laboratory. The power conversion system and reactor will be integrated to form the complete nuclear power module.
"These contract actions not only reduce technical risk and help us maintain momentum toward our 2028 launch, but they also strengthen collaboration across our partners," said Steve Sinacore, SR-1 Freedom program director.
The spacecraft by the numbers
NASA's mission page lists these specs for SR-1 Freedom:
- Mass: about 26,455 pounds (12,000 kilograms)
- Fuel: high-assay low-enriched uranium (HALEU)
- Reactor power: a 20-kilowatt-electric closed Brayton cycle power conversion system
- Spacecraft bus: a Power and Propulsion Element generating 48 kilowatts of electrical power
- Thrusters: the Advanced Electric Propulsion System, a 12-kilowatt Hall thruster
- Communications: X-band, through NASA's Deep Space Network
Safety: the reactor stays off until it leaves Earth orbit
NASA says it and the DOE are applying safety standards throughout the design, including interagency safety reviews, continuous oversight by a NASA chief safety officer, regulatory compliance and a design process focused on hazards, failure tolerance and nuclear safety. The reactor will remain inactive until the spacecraft leaves Earth orbit.
Three helicopters for Mars
SR-1 Freedom is targeting launch in late 2028, using that year's Mars launch window. Along with demonstrating nuclear electric propulsion, it will deliver SkyFall, a science payload made up of three Mars helicopters evolved from the design of NASA's Ingenuity helicopter.
According to NASA, SkyFall will deploy the helicopters in mid-air. They will carry ground-penetrating radar and imagers and measure air temperature, wind speed and wind direction. The goals are to collect scientific data, scout potential exploration zones and identify possible sources of water ice beneath the surface. NASA says the helicopters could last months, and potentially years.
A stepping stone to the Moon Base
NASA describes SR-1 Freedom as a pathfinder. The agency says flying a reactor first, without the added complexity of a lunar landing, reduces nuclear flight risk and helps build the supply chain and workforce for future missions. The mission is meant to inform Lunar Reactor-1, a fission surface power system designed to keep NASA's planned Moon Base running through periods of darkness and in places where solar power alone isn't enough.
NASA and the DOE have also signed a memorandum of understanding on space nuclear power and propulsion, covering work from research and fuel production to testing, launch integration and operations. The agreement takes effect November 1.
