Antares wins $161M from the Space Force to put fission back in orbit

A program office sizing a spacecraft power budget needs two numbers before it can pick anything: electrical output at the load, and mass on the bus. Interesting Engineering's account of the award carries neither for the R1-S or for Mark-1, and it sets neither reactor against the solar arrays and batteries a satellite uses now ^[16]. Without those figures, a bus designer has nothing to trade.

Antares says continuous electrical output could carry heavier computing workloads and directed-energy systems, and let a spacecraft maneuver without quickly exhausting limited power reserves ^[14]. The reactor that exists is on the ground: Mark-0 reached initial criticality at Idaho National Laboratory on June 4 under a Department of Energy authorization, and Antares was the first private company to do that inside the Reactor Pilot Program ^[7][8].

The Space Force money buys the next steps. Most of them happen on Earth. R1-S gets demonstrated on the ground, and only after that is it integrated with a spacecraft for flight certification ^[3]. Mark-1 makes electricity on a closed Brayton cycle and is expected to run for more than six months during its campaign ^[6]. A campaign that begins early in 2027 and runs six months ends no sooner than the middle of that year. That leaves roughly 18 months before the end of 2028, the earliest date Executive Order 14369 asks for ^[11][19].

The award is $161 million against the $470 million Antares raised in a Series C in July, or about 34 percent of that round ^[18]. Interesting Engineering describes the award as among the largest current US defense investments in space nuclear power ^[2].

The publication reports that Jordan Bramble, the CEO and co-founder, said Antares has pursued space applications since its founding, and that he described the award as the point where that ambition became an official mission ^[10].

Whether to design around this depends first on whether the payload load actually exceeds what an array and battery deliver at end of life. It depends next on whether the program schedule can absorb a ground demonstration, spacecraft integration and flight certification ^[3]. A no on the first part means nothing in this award changes the design. A no on the second means the sensible move is a solar baseline with the reactor held as a later block upgrade.

The compute premise behind all of it is an assertion. The source says military satellites demand more computing power and advanced onboard systems ^[15], and gives no figure for current draw or growth rate ^[16]. The US has flown one reactor in space, SNAP-10A, launched by NASA in 1965 as an experimental system ^[13]. A 2028 flight would arrive 63 years after it ^[17].