Space Reactor‑1 Freedom
Proposed nuclear-powered spacecraft
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Space Reactor-1 Freedom (SR-1) is a proposed NASA spacecraft intended to be the first nuclear fission-powered interplanetary mission and to demonstrate nuclear electric propulsion in deep space.[1] Announced in March 2026, the spacecraft would combine a closed Brayton cycle fission reactor generating more than 20 kW of electrical power with the Power and Propulsion Element (PPE) previously developed for the Lunar Gateway space station. The reactor is to be fuelled by high-assay low-enriched uranium (HALEU), using uranium dioxide fuel encased in a boron carbide radiation shield.[2]
- PPE: Lanteris Space Systems
- Thrusters: Aerojet Rocketdyne, Busek and NASA
 Rendering of Space Reactor-1 Freedom | |
| Mission type | Nuclear electric propulsion technology demonstration |
|---|---|
| Operator | NASA |
| Spacecraft properties | |
| Manufacturer |
|
| Power | >20 kW of electrical power from reactor |
| Start of mission | |
| Launch date | 2028 (planned) |
For propulsion, the PPE is equipped with four 6 kilowatt (kW) Hall-effect thrusters built by Busek and three 12 kW Advanced Electric Propulsion System Hall-effect thrusters developed by NASA and Aerojet Rocketdyne.[3][4]
SR-1 is proposed for launch in December 2028 on a trajectory to Mars.[2] It will demonstrate the technology to potentially reduce travel time, but will not at this size be significantly faster than previous probes.[5] At Mars it would deploy the Skyfall payload—an entry capsule carrying three Ingenuity-class helicopters to scout potential landing sites for future human missions and survey subsurface water ice.[6]
The mission, jointly sponsored by NASA and the United States Department of Energy, is intended to demonstrate nuclear propulsion and power technologies for sustained exploration beyond the Moon, including future missions to Mars and the outer Solar System. Data from SR-1 is also expected to support development of Lunar Reactor-1 (LR-1), a fission surface power system designed to provide continuous energy for a lunar base during periods without sunlight.[7]
