Original Coverage & Source Attribution: www.innovationnewsnetwork.com
As space exploration technologies accelerate, an engine that can traverse deep space equally fast is needed- and nuclear engines could be the answer.
For decades, spacecraft have relied largely on chemical rockets to make the major manoeuvres needed to leave Earth and travel between planets. That approach has enabled missions across the Solar System, but it comes with a fundamental limitation: carrying the large quantities of fuel and oxidiser required for high-thrust propulsion adds mass and constrains what a spacecraft can do.
Nuclear propulsion is being investigated as one way to break that constraint. NASA is developing both nuclear thermal propulsion (NTP) and nuclear electric propulsion (NEP), while the European Space Agency (ESA) has recently completed studies examining nuclear systems for missions to the Moon, Mars and beyond.
The attraction is not simply greater speed. Nuclear systems could combine high energy density with more efficient use of propellant, potentially allowing spacecraft to carry more useful payload, spend less time in transit and operate farther from the Sun. But turning those advantages into operational spacecraft remains a significant engineering and safety challenge.
Why chemical propulsion reaches its limits
Chemical propulsion remains the dominant technology for launching spacecraft because it can generate enormous thrust. A chemical rocket burns fuel with an oxidiser, producing hot gases that are expelled through a nozzle to accelerate the vehicle.
The problem emerges once a spacecraft is travelling between planets.
A chemical spacecraft must carry both its fuel and oxidiser, and increasing the amount of propellant also increases the mass that has to be accelerated. This creates a difficult trade-off between fuel, payload and mission performance.
Mars provides a useful example. ESA says a conventional chemically propelled journey to Mars takes around nine months. Reaching the planet more quickly requires significantly more energy and propellant, creating difficult constraints for missions carrying people or large amounts of equipment.
This is where nuclear propulsion could offer a different approach.
Rather than obtaining energy from a chemical reaction, nuclear systems use energy released through nuclear fission. That energy can either heat a propellant directly or generate electricity to power an electric thruster.
The two approaches have very different characteristics.
Nuclear thermal propulsion: high thrust from a reactor
Nuclear thermal propulsion is perhaps the most direct alternative to a chemical rocket.
In an NTP engine, a nuclear reactor heats a propellant, typically hydrogen, to extremely high temperatures. The hot gas is then expanded through a nozzle to produce thrust.
The reactor therefore replaces the combustion chamber and chemical reaction that would normally provide the heat.
The benefit is efficiency. NASA says NTP can provide approximately twice the propellant efficiency of chemical propulsion while retaining high thrust.
That combination is particularly valuable for deep-space missions, where a spacecraft needs both substantial changes in velocity and efficient use of its available mass.
NTP also has a long development history. The United States conducted extensive nuclear rocket research through programmes including NERVA in the 1960s and 1970s, although no nuclear thermal rocket has yet flown in space. NASA notes that the last US nuclear thermal rocket engine tests took place more than 50 years ago.
The technology is now being revisited with modern materials, reactor designs and manufacturing techniques.
Europe is revisiting nuclear rockets
ESA is among the organisations now examining whether nuclear propulsion could become part of Europe’s future exploration architecture.
In 2025, ESA completed its Alumni study into nuclear thermal propulsion. The work involved ESA, the French Alternative Energies and Atomic Energy Commission (CEA), ArianeGroup and Framatome Space.
The study examined a new nuclear thermal propulsion design intended for missions to the Moon and Mars and concluded that the concept was feasible in the long term, while identifying significant technology-development requirements.
The proposed system would use a ceramic-metal reactor core and hydrogen propellant. ESA says the design could be particularly suited to heavy spacecraft requiring large changes in velocity.
Safety was a central element of the study. The proposed reactor would not be activated until the spacecraft had reached a safe orbit away from Earth. ESA says the fresh uranium fuel would have very low radioactivity before activation, while radiation shielding would be required during operation to protect the spacecraft and crew.
However, ESA is clear that this is still a development programme rather than a ready-to-fly propulsion system. Further laboratory testing is needed, including work on fuel production, reactor components and facilities capable of safely testing the technology.
Nuclear electric propulsion takes a different route
Nuclear electric propulsion could be even more efficient, although it sacrifices thrust.
Instead of using reactor heat directly to propel the spacecraft, an NEP system uses a nuclear reactor to generate electricity. That electricity then powers an electric thruster, which accelerates a propellant to produce thrust.
Electric propulsion already has a track record in space. ESA describes electric propulsion as highly mass-efficient because it can accelerate propellant to much higher velocities than conventional chemical systems, although the resulting thrust is relatively low.
The limitation for conventional solar-electric propulsion is power. As spacecraft travel farther from the Sun, solar energy becomes less readily available.
A nuclear reactor changes that equation.
NASA describes NEP as a system capable of operating for long periods with very high propellant efficiency. The spacecraft accelerates gradually, rather than producing the powerful thrust associated with a conventional rocket.
That makes NEP potentially attractive for missions where a spacecraft can spend a long time accelerating, including some missions to Mars and destinations farther into the Solar System.
NASA is testing the building blocks
NASA’s recent work demonstrates that nuclear electric propulsion is not simply a theoretical concept.
In February 2026, NASA’s Jet Propulsion Laboratory tested a lithium-fed magnetoplasmadynamic thruster at power levels exceeding those of previous US electric propulsion tests. The technology is being investigated as a potential component of future nuclear electric propulsion systems.
The development team is targeting power levels between 500 kilowatts and 1 megawatt per thruster. NASA says a human Mars mission could require around 2–4 megawatts of propulsion power, potentially requiring several such thrusters operating for extended periods.
The test is significant because it addresses one of the central problems facing NEP: generating and managing enough electrical power to produce useful thrust.
The thruster itself is only part of the system. A nuclear electric spacecraft would also require a reactor, power-conversion equipment, radiators to reject waste heat, shielding and high-power electrical systems.
That makes NEP a complex systems-engineering challenge rather than simply an exercise in developing a more powerful engine.
Europe is looking beyond Mars
ESA is now examining these technologies as part of a broader long-term exploration strategy.
Its Rocketroll study, completed in 2026, investigated European concepts for nuclear electric spacecraft. Three consortia developed different designs, examining everything from reactor technologies to safety, operations and ground infrastructure.
ESA says the designs considered electrical power ranging from hundreds of kilowatts to several megawatts. Potential applications include missions to the outer planets and lunar missions requiring power through the Moon’s 14-day night.
The study identified a rough dividing line between solar-electric and nuclear-electric systems at around 100 kilowatts of power demand. Below that level, solar-electric propulsion can remain advantageous, while missions requiring substantially more power could benefit from nuclear generation.
The implications extend beyond propulsion.
A nuclear reactor could provide electricity for spacecraft instruments, communications and other systems as well as the propulsion system. That could become increasingly valuable as missions travel into regions where sunlight is weak.
The Mars advantage
Mars is one of the clearest potential applications for nuclear propulsion because it sits at the intersection of several challenges.
A crewed Mars mission would need to transport people, life-support equipment, supplies and other hardware across millions of kilometres while limiting the time astronauts spend in transit.
Shorter journeys could reduce exposure to the hazards associated with prolonged spaceflight, including cosmic radiation and microgravity.
NASA has therefore examined nuclear propulsion specifically in the context of human Mars missions. Its nuclear thermal propulsion work is aimed at developing low-enriched uranium systems capable of providing the high thrust and improved propellant efficiency required for such missions.
Nuclear electric propulsion offers another possibility. NASA says its low-thrust approach could accelerate spacecraft over extended periods while using substantially less propellant than high-thrust systems.
Neither approach, however, guarantees a short journey to Mars. Mission duration depends on spacecraft mass, trajectory, propulsion performance, power availability and the timing of planetary positions.
Nuclear propulsion is better understood as a technology that could expand the range of feasible mission architectures rather than a single solution to the challenges of interplanetary travel.
Safety remains a fundamental challenge
The prospect of launching a nuclear reactor on a rocket inevitably raises safety questions.
The central issue is controlling the risk associated with a launch failure and ensuring that nuclear material does not create unacceptable consequences on Earth.
For proposed systems, one approach is to launch the reactor in an inactive state and only start the nuclear reaction once the spacecraft has reached a safe orbit. ESA’s Alumni study follows this principle.
Once operational, additional challenges arise. Nuclear thermal engines must withstand extreme temperatures, while nuclear electric systems need large radiators to dispose of waste heat. Shielding is also required to protect spacecraft electronics and, for crewed missions, astronauts.
NASA’s current nuclear thermal propulsion work highlights the severity of the engineering environment: reactor technology must operate at temperatures exceeding 2,800 kelvin in a flowing hydrogen environment.
These are demanding requirements, and they explain why nuclear propulsion remains under development despite decades of research.
A propulsion system for a different era of exploration
Nuclear propulsion is not likely to replace chemical rockets across the entire space industry. Chemical systems remain extremely effective when very high thrust is required, particularly during launch from Earth.
Instead, nuclear systems could occupy a different role: moving large spacecraft efficiently once they are already in space.
Nuclear thermal propulsion offers a combination of high thrust and improved propellant efficiency, while nuclear electric propulsion offers extremely high propellant efficiency and sustained low thrust. Together, they could give mission designers options that are difficult to achieve with chemical and solar-powered systems alone.
The technology is still some way from routine operational use. NASA’s nuclear thermal programme remains focused on technology development, while ESA’s recent studies have identified laboratory testing and further technology maturation as necessary next steps.
But the direction of research is becoming clearer. As exploration moves beyond short-duration missions near Earth and towards Mars, the outer planets and more demanding robotic science missions, propulsion becomes one of the biggest constraints on what spacecraft can accomplish.
Nuclear propulsion will not make deep space easy to reach. What it could do is change the engineering limits around how much spacecraft can carry, how much power they can generate and how quickly they can move between worlds.
For a new generation of exploration, that could prove just as important as the rockets that first carried humanity beyond Earth.
