Why this class exists
Past the Belt and on Mars, Fission Is the Power Plant
Sunlight falls to 3.7% of Earth's at Jupiter and Martian dust storms cut solar output for weeks; every outer-system and Mars plan assumes a reactor.
The United States has flown one reactor, SNAP-10A, in 1965. The current lunar requirement has moved twice in a year: NASA's August 2025 directive called for 100 kWe on the Moon by 2030, and the August 2026 draft solicitation for Lunar Reactor-1 asks for 20 kWe. The first flight article on the books is SR-1 Freedom, a 20 kWe nuclear-electric pathfinder built on the former Gateway Power and Propulsion Element, launching to Mars in December 2028. Building
The industrial question is specific power - watts per kilogram of reactor, converter and radiator together - because it sets how fast a nuclear-electric ship can reach Ceres or Callisto. The Presence Gate reads it directly: crewed missions to the Belt need a 10-20 MWe ship, three orders of magnitude above anything in this table. Modeled
US fission
The Lunar Requirement Fell From 100 kWe to 20 kWe in a Year
NASA, DOE, the Space Force and the Air Force are each funding small reactors; none has flown.
| Program · organization | Power | Status | Rated |
|---|---|---|---|
| Lunar Reactor-1 (LR-1) · NASA | 20 kWe minimum (draft) | August 2025 directive asked for 100 kWe by 2030; the 30 August 2026 draft SPARC solicitation drops the floor to 20 kWe, five years unattended, through 354-hour lunar nights. No award yet | Building |
| SR-1 Freedom · NASA | ~20 kWe · 48 kW electric propulsion | Announced March 2026; HALEU heat-pipe reactor with Brayton conversion on the former Gateway Power and Propulsion Element; launches to Mars December 2028 carrying SkyFall with three helicopters | Building |
| DRACO · DARPA, Lockheed Martin, BWXT | Nuclear thermal | Cancelled 30 May 2025 after $499M; DARPA cited falling launch costs | Observed |
| Antares R1-S and Mark-1 | Heat pipe and Brayton | Mark-0 reached criticality at Idaho National Laboratory 4 June 2026; $161M Space Force award 11 September 2026; ground test 2027 | Observed |
| eVinci · Westinghouse | 5 MWe commercial | Zero-power criticality at the Nevada National Security Site 24 August 2026 | Observed |
| Advanced Nuclear Power for Installations · US Air Force | ~1 MWe | Radiant, Antares and Westinghouse selected April 2026; Radiant unit to Buckley Space Force Base by 2028 | Building |
Radioisotope power
Plutonium-238 Supply Still Sets the Pace of Outer-System Science
Radioisotope generators power probes; americium and strontium are the commercial alternatives.
| System · organization | Output | Status | Rated |
|---|---|---|---|
| Pu-238 production · DOE, Oak Ridge | 1.5 kg per year goal | Goal set for 2026; last confirmed shipment 0.5 kg in June 2023 | Building |
| Next-Gen RTG Mod 1 · NASA, DOE | ~250 W | Critical design review April 2026; early-2030s missions | Building |
| Dragonfly MMRTG · NASA, APL | ~110 W | Falcon Heavy no earlier than July 2028; Titan 2034 | Building |
| Zeno Power | Am-241 and Sr-90 | Am-241 supply from Orano (September 2025); NASA lunar radioisotope power system | Building |
| Am-241 heater unit · ESA | Heat | First full-scale core April 2026; first use on Argonaut around 2030 | Building |
Fuel
High-Assay Low-Enriched Uranium Is Scaling in Ohio
HALEU fuels every small reactor on this page, and the Russian supply route closes in 2028.
| Item | Figure | Status | Rated |
|---|---|---|---|
| HALEU from Centrus, Piketon, Ohio | >1,900 kg delivered | $900M DOE task order finalized 6 July 2026; first 12 t per year of new capacity by 2029 | Observed |
| DOE HALEU allocations | NASA and Radiant | Conditional commitments 27 July 2026, including fuel for SR-1 | Observed |
| Russian uranium import ban | Waivers end 1 January 2028 | In force since 11 August 2024; Russia restricted exports to the US in November 2024 | Observed |
China and others
China and Russia Plan a Lunar Reactor for 2035
The ILRS reactor is the reason the August 2025 US directive gave for its urgency.
| Program | Scale | Status | Rated |
|---|---|---|---|
| ILRS lunar nuclear power station · CNSA and Roscosmos | Surface reactor | Agreement May 2025; delivery 2035, completion around 2036 | Projected |
| Chang'e-3 radioisotope units · CNSA | Heat and power | Flew 2013 | Observed |
| Vehicle-mounted microreactor · FDS consortium, China | 10 MWe | Tested 30 April 2026; space named as one application | Observed |
| TEM / Zeus nuclear tug · Roscosmos | 1 MWe | Orbital test no earlier than 2030 | Projected |
| Lunar micro-reactor · Rolls-Royce, UK | 100 kW goal | Put on indefinite hold February 2026 | Observed |
Contested
Deliberately Not Claimed
The load-bearing uncertainties, tagged with the confidence they actually earn.
No space reactor has flown from the West since 1965. Every power figure for Mars, the Belt and the outer system assumes a reactor class that exists only in ground tests.
Launch approval is regulatory. Reactor launches go through the NSPM-20 authorization process. A tightened regime would delay every program above without any technical failure.
Megawatt-class propulsion is the gate for crewed missions past Mars. SR-1 at 20 kWe is a pathfinder. The ships that would move the Belt and Callisto across the Presence Gate are 500-1,000 times larger.
Record
Provenance and Data Sources
- Confidence
- Observed for flown, fielded or measured - Building for hardware and programs in development - Projected for announced plans - Modeled for original analysis
- Status date
- Q4 2026
- NASA
- Fission surface power directive (4 August 2025); SR-1 Freedom announcement (March 2026); draft SPARC solicitation (30 August 2026)
- Industry and defense
- DARPA DRACO cancellation (30 May 2025); Antares criticality (4 June 2026) and Space Force award (11 September 2026); Westinghouse eVinci criticality (24 August 2026)
- Fuel
- DOE Centrus task order (6 July 2026); DOE HALEU allocations (27 July 2026); Prohibiting Russian Uranium Imports Act
- China and Russia
- CNSA-Roscosmos lunar power station agreement (May 2025); FDS microreactor test (30 April 2026)
- Weakest link
- Specific power of flight reactors is unmeasured