NASA's SR-1 Freedom Would Be the First Fission-Powered Interplanetary Craft, Carrying Three Helicopters to Mars

NASA says work is moving forward on what would be the first nuclear fission-powered spacecraft ever sent beyond Earth orbit. Its official name is Space Reactor-1 Freedom, or SR-1 Freedom, and the agency is targeting a launch as early as 2028.

The project was first disclosed this spring at a NASA event called Ignition. That same event announced a change of plans for the Artemis Moon exploration program and the scrapping of the Gateway lunar space station. The nuclear spacecraft was part of the same announcement, and the latest update is the first real look at how far along it is.

SR-1 refers to both the reactor and the spacecraft built around it. The ship's job is to carry three exploration helicopters, collectively called SkyFall, to Mars. The nuclear power module is the centerpiece and sits at the back of the spacecraft's boom. The reactor generates heat through fission, and a conversion system turns that heat into electricity for the ship's systems and its electric propulsion. NASA has kept the reactor's exact components and features under wraps.

The conversion system is a Brayton cycle design, which uses a gas as the working fluid to turn thermal energy into electrical power. A company called Sierra Lobo is building it. It will be integrated with the reactor, which is being developed at the Department of Energy's Idaho National Laboratory. NASA says it is working with the DOE to make the reactor as safe to operate as possible.

The implications reach past Mars. If Freedom succeeds, it is likely to shape the design of future spacecraft bound elsewhere in the solar system. A nearer-term example is the Lunar Reactor-1, or LR-1, a surface power system planned for the upcoming Moon Base. It would keep the base running through the Moon's long stretches of darkness and cold. That setup is more complex, since it requires a lander to put the hardware on the surface, which is why NASA chose to fly a reactor first on a spacecraft instead.

The cargo is three helicopters inspired by Ingenuity, the small rotorcraft that first showed powered, controlled flight on another planet is possible. NASA is developing them with AeroVironment, which also worked on Ingenuity. They will be released mid-air from inside an entry capsule, so no lander is needed to get them to the surface.

Each helicopter will carry a substantial instrument suite: ground-penetrating radar, imagers, and cameras for photographing the terrain below. The instruments will measure air temperature, wind speed and direction, and subsurface features. That data will be used to map terrain and characterize parts of Mars that have never been studied, including at different elevations. SkyFall's stated goals are to identify potential water sources and subsurface ice and to build a meteorological data set.

Even though they are deployed in the atmosphere, the helicopters will have to land from time to time. NASA is still choosing a landing area and is looking for flat, low-elevation ground free of geological obstacles, where the three machines could in principle operate for years. The helicopters are at an advanced stage of development, and testing was last discussed publicly in the summer.

Ingenuity set the benchmark. It flew 72 times, covering 10.5 miles (17.0 km) and spending a combined two hours in the thin Martian air. What to watch next: progress toward the 2028 launch window, the reactor safety work with the DOE, and the choice of a landing site for the helicopters.