The US Defense Innovation Unit (DIU) is advancing two different approaches to accelerate ground and flight testing for nuclear-powered prototypes: compact fusion and next-gen radioisotope concepts. The ultimate objective is to launch a successful orbital prototype demonstration in 2027 of each approach.

DIU has awarded two Prototype Other Transaction (OT) contracts: one to the Ultra Safe Nuclear and a second to Avalanche Energy to demonstrate the next generation of nuclear propulsion and power capability for spacecraft. Specifically, these companies will be testing solutions that give small spacecraft the ability to manoeuvre at-will in cislunar space and enable high-power payloads that will support the expansion of Department of Defense (DOD) space missions.

“Advanced nuclear technologies will provide the speed, power, and responsiveness to maintain an operational advantage in space,” said US Air Force Major Ryan Weed, Programme Manager for the Nuclear Advanced Propulsion and Power (NAPP) programme at DIU. “Nuclear tech has traditionally been government-developed and operated, but we have discovered a thriving ecosystem of commercial companies, including start-ups, innovating in space nuclear."

Ultra Safe Nuclear’s pilot will demonstrate a chargeable, encapsulated nuclear radioisotope battery (called EmberCore) for propulsion and power applications in space. This ‘next-gen’ radioisotope system will be able to scale to 10 times higher power levels, compared with plutonium systems, and provide more than 1 million kWh of energy in just a few kilograms of fuel.

Avalanche Energy has developed a device called an “Orbitron,” which utilises electrostatic fields to trap fusion ions in conjunction with a magnetron electron confinement scheme to overcome charge density limits. The resulting fusion burn then produces the energetic particles that generate either heat or electricity, which can power a high-efficiency propulsion system. Compared with other fusion concepts, Orbitron devices are promising for space applications as they may be scaled down in size and enable their use as both a propulsion and power source.

Future missions will demand more manoeuvrability and electrical power to expand the capabilities of spacecraft, allowing for orbital changes, methods to control or facilitate de-orbiting, the transfer of materials between orbits and solar shadow operations to name a few, etc. DIU expects that its NAPP programme will have a direct impact on how the US employs space power, ushering in an era where spacecraft can manoeuvre tactically in cislunar space.

As the DOD continues to source smaller and disaggregated spacecraft, there are a number of complementary efforts that support alternative solutions for nuclear propulsion and power.  The Defense Advanced Research Projects Agency (DARPA) and NASA are pursuing nuclear fission approaches for larger spacecraft. DIU’s programme is targeted at highly manoeuvrable, small spacecraft using fusion and radioisotopes. “Bottom line, chemical and solar-based systems won’t provide the power needed for future DoD missions,” said Major Weed.