SR-1 Freedom

SR-1 Freedom (notional concept) [NASA]

The SR-1 Freedom (Space Reactor 1 Freedom) is a proposed nuclear-electric propulsion technology demonstrator spacecraft developed by NASA in cooperation with the United States Department of Energy. Announced in 2026, the spacecraft is intended to become the first interplanetary mission powered by a nuclear fission reactor and is scheduled for launch toward Mars in December 2028.

SR-1 is jointly sponsored by NASA and the United States Department of Energy as part of broader efforts to develop long-duration nuclear power systems for spaceflight. Mission data is expected to support development of Lunar Reactor-1 (LR-1), a proposed lunar surface fission power system intended to provide continuous electrical power for future lunar bases during extended lunar night periods.

The mission is intended to demonstrate nuclear electric propulsion technologies for future deep-space exploration missions beyond the Moon, including crewed Mars expeditions and outer Solar System missions. At Mars, SR-1 would deploy the Skyfall payload, an atmospheric entry capsule carrying three Ingenuity-class helicopters intended to scout future human landing sites and investigate subsurface water ice deposits.

SR-1 combines a closed Brayton-cycle nuclear fission reactor with the Power and Propulsion Element (PPE) originally developed for the Lunar Gateway station. The reactor is designed to generate more than 20 kilowatts of electrical power using high-assay low-enriched uranium (HALEU) uranium dioxide fuel. Radiation shielding is provided by boron carbide structures surrounding the reactor assembly. The spacecraft uses solar-electric propulsion hardware integrated into the PPE section.

The propulsion system consists of four 6 kW Hall-effect thrusters manufactured by Busek together with three 12 kW Advanced Electric Propulsion System Hall thrusters developed by NASA and Aerojet Rocketdyne. Electrical power from the reactor would continuously operate the propulsion system during the interplanetary cruise phase.

The launch vehicle would place SR-1 onto an Earth-escape trajectory before activation of the nuclear reactor. This approach is intended to avoid operation of the fission system in Earth orbit. A Falcon-Heavy (Block 5)(ex) launch vehicle originally ordered for the PPE/HALO Lunar Gateway launch could potentially be reassigned for the SR-1 mission.