U.S. Space Force taps California startup for orbital nuclear reactor

The US Space Force awarded California startup Antares a $161 million Strategic Breakthrough contract to advance compact nuclear power for space missions. The effort covers an R1-S ground demonstration, spacecraft integration, and an eventual orbital flight, while a separate Mark-1 reactor is intended to power an operational ground-to-space asset. Antares previously took its Mark-0 prototype critical at Idaho National Laboratory on June 4, 2026, with federal and Army observers present. Testing of the Mark-1 system is planned for 2027, but the service has not announced a launch date or final operational platform.