This article was updated on April 22, 2024, to reflect USRA’s recent headquarters relocation.

A concept image of NASA’s Fission Surface Power Project. Credit: NASA

NASA is banking on nuclear power to extend future space exploration missions and facilitate a sustained human presence on the moon. The Universities Space Research Association, which relocated its headquarters from Columbia to Washington, DC, in October 2023, acknowledged the implications of fission’s growing importance in its March 2024 symposium on Space Nuclear Technology.

“Most agree that nuclear propulsion will be required for any crewed mission to Mars,” said USRA President and CEO Jeffrey Isaacson, adding that the Defense Advanced Research Projects Agency expects to demonstrate a nuclear thermal rocket in orbit as early as 2026.

According to DARPA, NTRs offer a significantly higher thrust-to-weight ratio than conventional space propulsion technologies and could considerably shorten flight times to distant exploration targets.

In addition to spaceflight, “Becoming comfortable with a fission power source and working with it on the moon is absolutely a priority,” said Scott Pace, director of the Space Policy Institute. 

Commercial industry is expected to play a large role by developing a production line of small modular reactors, he said, lowering the cost and enabling more robotic space exploration.

Steve Jurczyk, former associate administrator for NASA, outlined the need for reliable and sustainable lunar surface power during a meeting of the Lunar Surface Innovation Consortium at the Johns Hopkins University Applied Physics Laboratory in 2020.

Nuclear surface power could provide an advantage “particularly if we’re going to do in situ resource utilization,” he said. “The systems to do the conversion processing are going to take more power than we’ve ever needed on the surface before.”

NEP or NTP?

Franklin Chang Diaz, CEO of Ad Astra Rocket Company, said narrow launch windows associated with chemical rockets do not pose the same problems for nuclear-powered craft, whose speed would enable them to tolerate significant delays triggered by equipment problems or weather.

“We need a transportation paradigm shift to enable humans to really become spacefaring,” Chang Diaz said.

Still, there are a lot of safety considerations.

“A nuclear electric propulsion system has to be assembled in space, but the nuclear thermal propulsion system can safely be built on Earth and launched,” said Anthony Calomino, NASA’s Space Nuclear Technology Portfolio Manager. “One of the gaps for both of them is what to do for ground testing capability, particularly when we (begin) doing human rating, and certifying and verifying the performance and safety of these systems.”

Roger Myers, a Seattle-based aerospace consultant, said the shortened travel time to reach distant moons and planets is important to research scientists who want the ability to work on multiple outer planetary missions.

“Right now they’re lucky if they get to do two missions in a career,” he said.

New concept

APL is already considering a nuclear electric propulsion system for its conceptual Persephone mission to Pluto and the Kuiper belt. That mission concept would address key questions raised by APL’s New Horizons mission, including whether Pluto has an ocean.

A white paper detailing engineering design studies for NEP systems, whose co-authors include Ralph McNutt, director of APL, suggests that nuclear propulsion would decrease the conceptual mission’s risk posture.

“[White paper authors] show that a 10-kWe NEP spacecraft can deliver 67% more payload with 2.4 years shorter flight time compared to the current radioisotope electric propulsion system,” the team said, and would also enable greater than four times the data rate at Pluto compared with the REP option.

There are short launch windows for a conceptual Persephone mission in early 2031 and early 2032, using a Jupiter flyby to gain speed. The next window doesn’t open until 2042.

High energy demand

In its draft Community Report on The Path to an Enduring Lunar Presence, still being finalized, the Lunar Surface Innovation Consortium managed by APL for NASA stresses that no single method of lunar surface power generation under development can meet the demand of 100 kW to support a lunar station on the scale of the International Space Station.

According to the draft report, NASA envisions the deployment of a lunar power generation system that includes Vertical Solar Array Technologies by the mid- to late 2020s, with the hope of integrating at least one 40 kW fission surface power system by 2030. Achieving those milestones would unlock the potential for lunar surface commercialization.

Meanwhile, Rockville-based X-energy has entered into a joint venture with Intuitive Machines, of Texas, to advance the design of a fission surface power system to deliver 40 kWe of nuclear fission-based power to the moon by 2028.

Harlan Bowers, president of X-energy, said the Nuclear Regulatory Commission is not yet ready to entertain the notion of a commercial application operating a nuclear reactor remotely using software, even on the moon.

“There is a lot of ground to break in demonstrating these space applications, but I see that ultimately benefiting us for terrestrial applications,” he said.

The remaining gaps and needs of meeting NASA’s lunar power demands can only be filled by building and testing hardware, Bowers said, and continuing to gain knowledge in pursuit of a small modular reactor with a mission life of 10 to 20 years that requires no maintenance.

“That,” he said, “is where the challenge lies.”