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Artist's rendering of the proposed SR-1 Freedom spacecraft.
COLORADO SPRINGS—A new White House initiative to develop space nuclear power directs NASA to develop a minimum 20-kW fission reactor and fly a variant to the lunar surface by 2030, with an eye on having high-power reactors ready to launch in the 2030s.
“This is the next giant leap,” NASA Administrator Jared Isaacman said April 14 at the Space Symposium here.
The National Initiative for American Space Nuclear Power directive, released April 14 by the White House Office of Science and Technology Policy (OSTP), clears NASA to demonstrate the mid-power reactor in an electric propulsion system instead.
As part of its revamp of the Artemis lunar exploration initiative, NASA last month unveiled a program to demonstrate nuclear electric propulsion in space in late 2028. NASA aims to launch the Space Reactor-1 (SR-1) Freedom mission, which includes a flyby of Mars to dispatch a trio of Ingenuity-class helicopters to scout for subsurface ice. If successful, SR-1 would become the first vehicle to demonstrate nuclear electric propulsion in deep space.
“We’re trying as quickly as possible to get our pathfinder underway,” Isaacman said.
The directive steers NASA to partner with multiple vendors to develop fission power systems, including the reactor and power conversion, through at least preliminary design review and ground tests. The directive said the agency should:
• Prioritize integrated designs for mid-power fission surface power and nuclear electric propulsion systems that make use of common elements, including reactor hardware, nuclear fuel, and technologies that have been matured and demonstrated.
• Design systems that are compatible with current launch vehicles or those that will be “readily available” by 2029.
• Downselect to no more than two designs within one year.
OSTP noted that NASA should consider developing one low-power reactor, capable of providing at least 1 kW-electric (kWe), if that would lower schedule risk and cost, and look for reactor designs that can support high-power levels up to at least 100 kWe.
For the SR-1 Freedom demonstration, the spacecraft would be launched directly into an Earth-escape trajectory. About 48 hr. later, the SR-1’s 20–25-kW high-assay low-enriched uranium (HALEU) fission reactor would begin producing electricity to power some of the spacecraft’s thrusters. The system taps heat from fission to drive a closed Brayton cycle gas turbine and generate electricity. That, in turn, would power ion thrusters for interplanetary travel.
NASA plans to repurpose the Power and Propulsion Element (PPE) of the now-canceled Gateway lunar station to serve as SR-1’s spacecraft bus. The solar-powered PPE, built by Lanteris (formerly Maxar), was designed with a total of seven Hall-effect ion thrusters—three high-power 12-kW thrusters and four lower-power 6-kW thrusters that would be used for station-keeping and orbit-raising—for a combined 50-kW solar electric propulsion system.
The PPE includes two massive Roll-Out Solar Arrays, built by Redwire Space, measuring about 34 ft. by 60 ft. The module was previously to be attached to the Northrop Grumman-built Habitation and Logistics Outpost and launched to become the first components of the Gateway.
NASA now plans to modify the PPE to also draw power from the fission reactor. “The reactor will provide power that we will back feed into PPE, both for mission systems, but also to power those electric thrusters, or a subset of them,” Steve Sinacor, NASA program executive for Fission Surface Power, said during a March 30 interview with Aviation Week.
Studies are underway to assess whether some of the PPE thrusters will exclusively draw power from the reactor or if all the thrusters can be conditioned for dual solar/nuclear power operations, he added.
Attached to the PPE would be an expandable 82—98-ft.-long boom/truss segment, and the other end of the boom would be the Nuclear Power Module (NPM), which includes the reactor, heat exchangers, power conversion system and radiators.
The U.S. has not flown a nuclear reactor in space since 1965. The System for Nuclear Auxiliary Program (SNAP)-10A, which launched on April 3, 1965, into a polar, low Earth orbit, was designed to produce more than 500 watts of electrical power for one year. A voltage regulator, unrelated to the SNAP reactor, failed after 43 days, bringing the demonstration to a close.
Since then, NASA has spent more than $20 billion on more than a dozen follow-on programs.
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