Antares

Antares builds compact fission microreactors in a factory. The R1 uses a heat-pipe-cooled core (liquid sodium) and HALEU TRISO fuel, and is rated from 100 kW to 1 MW of electricity. Target uses are remote military bases, industrial sites and, later, space and underwater power. It plans a proposal for NASA's Fission Surface Power program (100 kWe on the Moon by 2030).

In 2026 its Mark-0 reactor reached initial criticality at Idaho National Laboratory under the DOE Reactor Pilot Program, with BWXT and Army support. It was selected for the DIU and Air Force ANPI program, with a prototype at Joint Base San Antonio, and holds a DOE HALEU allocation plus a multi-year HALEU supply deal with Urenco. It raised a $470M Series C in July 2026 and reports over $600M raised in total. It expects to produce electricity in 2027.

Founded in 2023 by Jordan Bramble (CEO) and Julia DeWahl. Headquartered in Torrance, California, with sites in Idaho Falls and Aiken, South Carolina.