NASA plan to add a nuclear reactor to Gateway and fly it to Mars, explained

Background

If you associate “nuclear in space” with the warm glow of plutonium batteries on deep-space probes, you’re only getting part of the story. Radioisotope power systems (RTGs) use the natural heat from radioactive decay to make tens to a few hundred watts of electricity—quiet, reliable, and nowhere near a chain reaction. A nuclear reactor in space is different: it maintains a controlled fission chain reaction to generate kilowatts to megawatts of power on demand.

The United States has flown only one space reactor, SNAP‑10A, in 1965. The Soviet Union launched dozens of small naval-surveillance satellites with reactors in the Cold War era. Since then, the U.S. has relied on RTGs for distant missions and solar arrays for everything closer to the Sun. But there has always been a gap: missions that need far more power than RTGs can supply and more propulsive efficiency than chemical rockets can reasonably provide.

Two nuclear pathways are back in play for that gap:

Nuclear thermal propulsion (NTP): a reactor heats hydrogen propellant directly and expels it through a nozzle. It promises roughly twice the efficiency of chemical rockets and relatively high thrust, but it demands exotic fuels and cryogenic handling.
Nuclear electric propulsion (NEP): a reactor generates electricity that feeds high-efficiency electric thrusters. NEP has exceptionally high specific impulse and operates for months or years, sipping propellant. The tradeoff is low instantaneous thrust.

NASA’s lunar Gateway—the planned small station in a near-rectilinear halo orbit (NRHO) around the Moon—creates a new opportunity. It’s far from Earth, accessible by human crews, and already slated to host a power-and-propulsion module. That makes it an attractive place to assemble, activate, and test a fission system in deep space with on-orbit servicing and oversight.

What happened

NASA has begun sketching a practical path to reintroduce reactors to spaceflight by tying them to near-term infrastructure. The agency’s concept—laid out in recent planning documents and industry briefings—borrows Gateway as a nuclear proving ground, then turns the proven hardware into a Mars-bound spacecraft. The sequence looks like this:

Build a nuclear power and propulsion stage

Core elements would include a compact fission reactor fueled with high-assay low-enriched uranium (HALEU), power-conversion hardware (for example, closed Brayton-cycle turbines or advanced thermoelectrics), enormous deployable radiators to reject waste heat, an electric propulsion cluster (Hall-effect or ion thrusters), tanks for xenon or alternative propellant, and a robust avionics/thermal control system.
The system target is “megawatt-class” electrical output—several orders of magnitude more than RTGs and significantly beyond what solar arrays can deliver efficiently at Mars distances without becoming unwieldy.

Assemble and activate at Gateway

The reactor module would be launched subcritical (no chain reaction) and remain shutdown through ascent. Only after docking to Gateway and after a series of checkouts would controllers move it to a safe activation posture.
Startup and early operations would occur in cislunar space, far from Earth’s atmosphere and population. Gateway offers proximity for crew-assisted inspections if needed, while keeping humans at safe standoff during the reactor’s initial criticality and power ramp.

Run an extended flight demonstration near the Moon

Objectives include months to a year of stable electrical output, thermal performance validation across operating regimes, electromagnetic compatibility checks with neighboring systems, and long-duration firings of the electric thrusters.
This phase proves out fueling, radiation shielding strategies, control algorithms, and the choreography for throttling the reactor with load changes.

Depart for Mars as a cargo pathfinder

Once the system meets its marks, the reactor stage would undock and spiral out of lunar orbit under continuous electric thrust, gathering speed gradually.
The demonstration payload could be a logistics canister, a small habitat prototype, or a science package. The cruise might take many months, but with very high propellant efficiency. On arrival, options include insertion into high Mars orbit, delivery to a Mars moon, or positioning as a power/relay asset.

Safe end-of-life disposition

If the system remains healthy, it becomes a Mars-orbit infrastructure node. If not, NASA’s baseline includes disposal in a stable heliocentric graveyard trajectory—no reentry through Earth’s atmosphere and no uncontrolled lingering in cislunar space.

This is not a paper fantasy. It builds on several parallel lines of work:

Space nuclear power maturation: NASA and the Department of Energy (DOE) have advanced compact fission concepts over the past decade, including the Kilopower reactor ground demo and ongoing lunar Fission Surface Power efforts.
Electric propulsion heritage: Hall-effect and ion thrusters have flown for decades on commercial and science missions. Scaling to hundreds of kilowatts requires engineering, but not invention from scratch.
Cislunar testbed logic: Gateway’s orbit is stable and remote enough for nuclear activation, while its international character and periodic crew visits bring operational oversight that a free-flying demo would lack.

Crucially, the plan also slots into Mars mission architecture thinking. A nuclear-electric stage can pre-deploy cargo, logistics, and even a return stage to Mars orbit ahead of a human mission, de-risking windows and shrinking the chemical rocket stacks that would otherwise be required.

How it would work in practice

The powerplant

A space reactor optimized for NEP must be compact, controllable, and miserly with mass. The likely fuel is HALEU, enriched to under 20 percent U‑235—high enough to keep the core small, low enough to avoid the proliferation and policy burdens of highly enriched uranium. The core’s fission heat is converted to electricity either by:

Closed Brayton cycle: A hot working fluid (often a noble gas like helium-xenon) spins a microturbine linked to an alternator. Brayton machines can reach 20–30 percent efficiency and scale to megawatt class with modularity.
Advanced thermoelectrics or thermionics: Fewer moving parts but lower efficiency; more mass ends up in radiators to dump extra heat.

Large radiator wings are non-negotiable. Megawatts in, megawatts of heat out. Lightweight composite heat pipes and deployable trusses keep mass down while spreading the thermal load.

The thrusters

Electric propulsion turns kilowatts into gentle, persistent push:

Hall-effect thrusters or gridded ion engines accelerate ions—usually xenon—through electric fields to exhaust velocities 10–20 times faster than chemical plume speeds. The payoff is specific impulse in the thousands of seconds and a propellant tank measured in tonnes rather than hundreds of tonnes.
Alternative propellants like krypton or even argon are attractive for cost and availability. Their performance is somewhat lower than xenon but may be “good enough” at scale.

At a megawatt of electrical power, total thrust might be measured in tens of newtons—comparable to the weight of a few kilograms on Earth. It’s not much instantaneously, but applied for months it steadily reshapes orbits and can deliver cargo across interplanetary space with excellent mass efficiency.

Safety and oversight

Every U.S. space nuclear mission runs a gauntlet of reviews:

Design-for-safety: The reactor must remain subcritical in all credible launch aborts and impact scenarios. It is only brought critical in a safe orbit.
Independent risk assessment: An interagency nuclear safety board audits the design, modeling, and accident analyses.
Environmental compliance: A National Environmental Policy Act (NEPA) process culminates in a detailed Environmental Impact Statement and public comment.
Presidential launch approval: Historically required for missions carrying significant nuclear material.

Operating at Gateway doesn’t short-circuit any of this. Instead, it provides a controlled venue for activation and early operations, with the option to step in if something off-nominal appears.

Why now

Power hunger beyond Earth: Ambitions for sustained operations at Mars and in the outer solar system outstrip what practical solar arrays can deliver, especially when dust, distance, and night cycles bite.
Electric cargo lanes: NEP creates slow but steady “freight rail” to Mars—pre-placing habitats, ascent vehicles, and supplies so that human crews can launch lighter and safer.
Maturing tech: Decades of electric propulsion on satellites and progress in compact fission systems reduce the leaps required.
Strategic signaling: China and others are public about space nuclear ambitions. Demonstrating safe, productive use is both a technological and geopolitical marker.

What could still derail it

Budgets and priorities: Space nuclear work competes with crewed Artemis milestones, science missions, and Earth observation. If Gateway’s schedule slips or budgets tighten, a NEP demo could slide right with it.
Fuel supply: HALEU production in the U.S. is scaling from a low base. Reactor cores need reliable, domestic supply within specific timelines.
Partner dynamics: International partners have hardware and plans tied to Gateway. Any test that complicates operations or threatens schedules must clear diplomatic as well as technical bars.
Public perception: Launching nuclear material remains politically sensitive, even with rigorous safeguards and the reactor cold on ascent.

Key takeaways

NASA’s pathway to revive space reactors is pragmatic: test near the Moon, then repurpose the proven stage for a Mars cargo demo.
The approach marries a megawatt-class fission reactor to high-efficiency electric thrusters, trading months-long burns for dramatic propellant savings.
Gateway functions as both assembly node and safety buffer, enabling activation far from Earth while retaining crew access when appropriate.
Success would establish a nuclear-electric “freight lane” to Mars and de-risk human exploration by prepositioning heavy hardware ahead of crews.
The plan hinges on budgets, fuel supply, international coordination, and an exacting nuclear safety and environmental review process.

What to watch next

Procurement signals: Look for NASA and DOE to release industry solicitations specifying power levels, conversion tech, and thruster types.
HALEU ramp-up: Announcements of domestic enrichment milestones and fuel fabrication partnerships will be critical schedule drivers.
Gateway cadence: Launch dates for Gateway’s power and habitation elements, and clarity on long-term operations, will tell you whether cislunar testing can happen this decade.
Environmental documentation: Draft Environmental Impact Statements for space nuclear demos are public. Their timelines foreshadow launch windows.
Thruster selection: Downselects between high-power Hall thrusters, ion engines, or hybrid architectures will shape performance and propellant choices.
Mission design trade studies: Will the demo target high Mars orbit, a Mars-moon rendezvous, or serve as a long-lived power/relay asset after arrival?

FAQ

Q: Is this the same as the nuclear thermal rocket plans I’ve heard about?
A: No. Nuclear thermal propulsion uses a reactor to directly heat hydrogen propellant for higher-thrust maneuvers. This plan focuses on nuclear electric propulsion, where a reactor generates electricity for electric thrusters. NEP is far more efficient with propellant but offers much lower thrust.

Q: How is this different from the plutonium power sources on spacecraft like Voyager or Curiosity?
A: RTGs and radioisotope heaters rely on passive decay heat and produce modest power. A fission reactor maintains a controlled chain reaction, yielding kilowatts to megawatts of electricity—enough to drive powerful thrusters and run large systems continuously.

Q: Is it safe to activate a reactor near a crewed outpost?
A: Activation would be conducted with strict standoff and shielding protocols, and likely when no crew is nearby. The reactor is launched “cold” and only made critical in a stable, remote orbit. Extensive safety analyses, independent reviews, and environmental assessments are prerequisites to flight.

Q: Why not just use bigger solar arrays?
A: Solar works well near Earth and the Moon but becomes bulky and fragile at Mars distances, especially for megawatt-class power. Dust, night cycles, and eclipses further complicate operations. A compact reactor provides steady power independent of sunlight.

Q: When could a demo like this actually fly?
A: The earliest practical window is late 2030s to early 2040s, contingent on funding, Gateway availability, fuel supply, and the lengthy safety review process inherent to nuclear missions.

Q: Will they really send the whole Gateway to Mars?
A: The current thinking is to dock a dedicated nuclear power-and-propulsion stage to Gateway for checkout, then send that stage onward with its own payload. Gateway itself is expected to remain in lunar orbit to support Artemis operations.

Q: What happens at the end of life?
A: If healthy, the stage could serve as a long-duration power and communications node in Mars orbit. If not, mission plans include disposal to a stable solar orbit that avoids Earth reentry.

Q: Could this eventually carry astronauts to Mars?
A: In principle, yes—nuclear-electric stages are often envisioned as the backbone of a “Deep Space Transport” for crew. The initial demonstration would almost certainly be uncrewed cargo, building confidence before any human-rated applications.

Source & original reading

Original article: https://arstechnica.com/space/2026/03/here-is-nasas-plan-for-nuking-gateway-and-sending-it-to-mars/

NASA’s audacious nuclear plan: turn Gateway into a test stand—then send the hardware to Mars