The yardstick reactor behind NASA's fission power buy

What the work claims

This is a program-of-record overview, not a research result, and it should be weighted as such: four slides by the FSP project manager stating what NASA intended to buy and how, as of November 2022. Its claims are specific. NASA would develop a space-qualified fission surface power flight unit before the end of 2028, with key design characteristics of 40 kWe output at 120 Vdc, a 6,000 kg mass limit so the system fits on a lander, a radiation dose no more than 5 rem per year above background at 1 km, and the ability to operate on the lander or be transported elsewhere on the surface.¹ The acquisition would run in two phases: one-year Phase 1 study contracts with three industry teams, followed by a separate, open, competitive Phase 2 procurement delivering a qualification unit and a flight unit.¹

The slide that matters most is the one that seems parenthetical: alongside the industry competition, NASA and the Department of Energy would develop a government reference concept, run power conversion maturation and nuclear technology maturation, and, in a note at the bottom, remind the reader that "industry will determine the design."¹ That tension, the government designing a reactor it explicitly will not build, is the analytical core of this piece.

How the procurement works

The later IAC 2024 status paper, written by the FSP team itself, shows what the overview's structure became in practice. Phase 1 awarded three $5M concept design study contracts in 2022, to Intuitive Machines with X-Energy, Lockheed Martin with BWXT, and Westinghouse with Aerojet Rocketdyne, completed in September 2023. Only three requirements were levied on the partnerships: produce 40 kWe for 10 years, have the reactor withstand launch and vibration loads, and keep the radiation dose at or below 5 rem per year above background at 1 km for astronaut safety.²

Three requirements is a deliberate mechanism. The 2024 paper states that the minimal number of requirements "allowed for innovative concepts to come forward," ensuring the return on investment NASA wanted, while the studies' challenges and risks informed what the government should ask for next.² In parallel, NASA Glenn and DOE's Los Alamos, Idaho, and Oak Ridge national laboratories executed the Government Reference Design against the same three requirements, with Glenn covering power conversion, heat rejection, power management and distribution, and mission integration. The GRD's stated objectives were to inform the acquisition, identify risks and opportunities for government technology investment, feed concepts to NASA architecture teams, and collect data to guide the Phase 2 request for proposal.² It investigated a transportable 40 kWe system on three separate pallets deployed from the lander, refined over three design analysis cycles between April and November 2023.²

Two arithmetic consequences of the 2022 spec deserve explicit boundaries. Forty kilowatts electric against a 6,000 kg ceiling implies a system-level specific power of about 6.7 W/kg; that is a derived ratio of a power requirement and a mass limit, not a measured specific power of any as-built hardware, and the 2024 paper confirms 6,000 kg remained a goal, not a demonstrated mass.¹² Likewise, 40 kW at 120 Vdc implies a bus current of roughly 330 A; the distribution voltage is a design requirement on a slide, not a tested power management and distribution architecture, though high-voltage transmission is named as a government technology maturation area.¹²

The strongest case for the structure

The steelman is information economics. A government that cannot design a space reactor cannot competently evaluate bids for one; every requirement it writes blind either over-prescribes and kills innovation, or under-specifies and invites unpriceable risk. The GRD squarely addresses this: by designing to the same three requirements the industry teams received, the government buys evaluation literacy at the cost of a few parallel design cycles, while the minimal-requirements competition keeps the design space open.² The 2022 overview's division of labor reinforces this: Idaho National Lab manages the industry contracts, Los Alamos provides reactor expertise, and the government concept matures the conversion technology rather than the reactor itself.¹

The hardware lineage behind the program is also real, if modest. The 2024 paper records that the 2018 Kilopower KRUSTY experiment demonstrated a flight-like system at prototypic conditions in a relevant environment, which the paper rates as Technology Readiness Level 5, and that the earlier full-scale Technology Demonstration Unit ran at full power under representative lunar conditions in a Glenn vacuum chamber with a 900 K reactor and Stirling conversion.² This is not a reactor on the Moon, but it is more integrated ground heritage than any US space fission program has had since the 1960s, and the 2022 plan of a fission system applicable to both the 14.5-day lunar night and weeks-long Mars dust storms is physically sound.¹

Where a skeptic should push

First, schedule honesty. The 2022 overview promises a space-qualified flight unit before the end of 2028.¹ The project's own 2024 paper states that the Phase 2 request for proposal, the step that starts the qualification and flight unit work, had not been released and its timing was pending FY25 budgets.² Two years after the plan of record fixed a 2028 flight unit, the competitive phase had not begun; any article treating the 2028 date as a forecast rather than a 2022 aspiration would be laundering a schedule target into a prediction.

Second, maturity honesty. As of the 2024 paper, Phase 1 had produced paper studies: three completed $5M concept contracts and a government reference design iterated through three analysis cycles.² No FSP reactor, shield, or power conversion unit exists; the most mature relevant hardware is a kilowatt-class ground experiment from 2018 and a non-nuclear full-scale TDU.² The 6.7 W/kg figure above is requirement arithmetic, and the 5 rem per year at 1 km constraint is a requirement on paper, not a verified shielding performance.

Third, the load-bearing assumption: that Phase 2 can deliver a qualification unit and flight unit without an integrated nuclear ground test campaign comparable to KRUSTY's. The 2024 paper's technology maturation list (closed Brayton and Stirling conversion, radiation-tolerant organics and electronics, additive-manufactured heater heads, heat pipes, metallic hydride moderators, high-voltage PMAD) is broad precisely because most of these are unproven at flight scale.² If FY budgets compress Phase 2, these maturation items, not reactor physics, are where mass and schedule will quietly break.

What a yardstick reactor means for space power

The non-obvious implication is that the reference design, not the winning contractor, may become the real product. The GRD's stated objectives include collecting data to guide the Phase 2 RFP requirements and feeding concepts to NASA architecture teams.² Whoever wins Phase 2 will design against requirements the government wrote by studying its own three-pallet, transportable, 40 kWe concept; the 2022 overview's "industry will determine the design" is true at the component level and nearly meaningless at the architecture level.¹ For the rest of the lunar power ecosystem, that is the de facto standardization mechanism: 40 kWe blocks, roughly 120 Vdc-class distribution, and lander-integrated delivery are the interface the future lunar grid will be built around, decided inside a government design cycle, not by an interface-control document.

The genuine threat is fiscal rhythm, and it is quantified by the program's own schedule. A lunar fission demo must arrive before the 14.5-day night it exists to survive; the 2028 target was already two years stale against the 2024 RFP status.¹² Because Phase 2's release was made contingent on a single fiscal year budget line, the program's entire architecture, including the minimal-requirements logic that was supposed to protect innovation, is exposed to annual appropriations. One skipped or trimmed cycle does not delay the program by one year; it forfeits a landing window and pushes demonstration past the next lunar night season, compounding at mission level.

The opportunity is transferable procurement machinery. The minimal-requirements study plus government yardstick design is a template that any hard-to-specify space power system could copy: a lunar beaming demo, a megawatt-class ISRU plant, a high-voltage surface grid. And the maturation list itself is cross-subsidized technology: the 2024 paper notes that of the five critical technology elements for nuclear electric propulsion, all but the electric propulsion subsystem are being worked under the FSP portfolio, including the high-voltage power transmission that any large surface power network will need.² A surface reactor program is quietly functioning as the funding vehicle for the PMAD and conversion technology that deep-space power at any scale will draw on.

The bottom line

Established with high confidence, because both cited records are NASA primary documents: the FSP program fixed a 40 kWe, sub-6,000 kg, 5 rem per year at 1 km specification, bought three competing $5M concept studies under three requirements only, and built a government reference design whose explicit purpose is to make the government a competent buyer. Established with high confidence: the 2028 flight-unit target stated in 2022 had slipped in practice, with Phase 2 solicitation timing still undecided as of October 2024, so the date is a historical plan of record, not a schedule. Unresolved: whether the minimal-requirements approach survives contact with a funded Phase 2, since the GRD's influence on the RFP requirements means the winning design will likely converge toward the government concept anyway. What would confirm the model is a released Phase 2 solicitation whose requirements leave the architecture open; what would break it is an RFP that simply asks industry to bid the government design, converting a yardstick into a blueprint.