NASA tests lithium thruster: Milestone for manned Mars missions?

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On February 24, 2026, a team at NASA's Jet Propulsion Laboratory in Pasadena, California, ignited a magnetoplasmadynamic thruster (MPD thruster) powered by lithium metal vapor for the first time. At power levels that, according to the agency, are said to surpass all previous US tests of this technology. The system reportedly achieved power levels of up to 120 kilowatts, more than 25 times the thrust of the currently most powerful electric engines NASA operates in space. The space agency and JPL only published their results last week.

The test was conducted in JPL's CoMeT chamber (Condensable Metal Propellant Vacuum Facility) – an 8-meter-long, water-cooled vacuum chamber designed for operating thrusters with metallic vapor propellants. NASA calls it a unique national testing instrument designed for power levels up to the megawatt range.

During a total of five ignitions, the tungsten electrode at the center of the thruster is said to have reached temperatures exceeding 2,800 degrees Celsius. JPL researcher James Polk stated that his team proved the thruster works and achieves the targeted power levels. Polk has been researching lithium MPD thrusters for years and was previously involved with NASA's Dawn probe and Deep Space 1 – the first interplanetary probe with an ion engine as its primary propulsion.

What is an MPD thruster?

The journey to Mars presents space travel with a fundamental propulsion problem. Conventional chemical rockets consume enormous amounts of fuel. According to NASA calculations, a spacecraft needs about 261 kilograms of fuel for every kilogram of payload – for a round trip to Mars, this would amount to between 1,000 and 4,000 tons. Furthermore, a chemically propelled spacecraft would take eight to nine months to reach Mars – a severe physical and psychological burden for any crew.

According to NASA, electric propulsion systems consume up to 90 percent less fuel than chemical rockets. Researchers are also working on propellant-free concepts: A team at Texas A&M University has developed a light-based drive with 3D control entirely without propellant, which could even enable interstellar travel in the long term. Classic ion thrusters – like those used by NASA's Psyche probe – accelerate a propellant gas electrostatically using solar power. However, they are hardly suitable for manned missions: Today's ion thrusters used by NASA, such as NEXT-C, produce a thrust of up to 236 millinewtons – comparable to the gravitational force acting on a postcard falling to Earth. This is not enough to bring a fully loaded spacecraft and its crew to their destination.

The MPD thruster is intended to resolve this dilemma: It uses high electric currents that interact with a magnetic field to electromagnetically accelerate the lithium plasma. The technology has been researched since the 1960s but has never been operationally used until now. According to NASA, lithium offers certain advantages: it can be efficiently ionized, has a low atomic mass, and enables high specific impulse, meaning efficient fuel utilization.

Where does the power come from? The role of nuclear energy

The MPD thruster is not a nuclear drive; it is an electric drive. However, it requires a powerful energy source, and this is where nuclear technology comes into play.

For a manned Mars mission, NASA assumes a total power requirement of 2 to 4 megawatts. This scale is hardly achievable with solar energy: the farther a spacecraft moves away from the sun, the weaker the solar radiation becomes – in the vicinity of Mars, solar panels provide only 40 to 50 percent of the power they do near Earth. Moreover, megawatt power levels would require impractically large panels.

The intended overall concept is called Nuclear Electric Propulsion (NEP): A compact nuclear reactor on board would generate electrical power to feed the MPD thrusters. The reactor would be the generator, and the thruster the actual engine. Nuclear electric propulsion systems can likely maintain their thrust for up to three hours – an advantage over nuclear thermal propulsion systems, which overheat and must pause after a few minutes. Both components – reactor and thruster – must be developed in parallel. This is the stated goal of NASA's “Space Nuclear Propulsion” program, which has been working on a megawatt-capable nuclear electric propulsion system for manned Mars missions since 2020.

NEP versus NTP: Two nuclear paths to Mars

To be distinguished from this is the also discussed Nuclear Thermal Propulsion (NTP), in which nuclear energy is used directly to heat and expel propellant. This is precisely the approach pursued by the joint DRACO program of NASA and DARPA, which will no longer receive funding in the NASA budget for 2026 and has therefore been canceled.

The thermonuc lear approach promises significantly higher thrust: According to NASA calculations, the thrust-to-weight ratio for nuclear thermal propulsion is about 10,000 times higher than for electric propulsion – including nuclear electric. On the other hand, NEP with MPD thrusters is more efficient in terms of propellant consumption. NASA states that it is pursuing both approaches in parallel.

Significant hurdles remain

The 120 kilowatts achieved in the test are a first step – but the actual target is much higher. The team plans to achieve power levels between 500 kilowatts and 1 megawatt per thruster in the coming years. For a manned Mars mission, several of these thrusters would have to be operated in parallel – and for over 23,000 operating hours. Whether and when this will succeed is uncertain.

The temperatures exceeding 2,800 degrees Celsius at the tungsten electrode reached during the test illustrate the enormous thermal stresses the system would have to withstand during continuous operation. Proving the long-term suitability of the materials is considered one of the central open questions for further development.

In addition, there are fundamental safety issues surrounding nuclear propulsion: If multiple fuel rods are necessary, they must remain safely separated from each other even during the vibrations of a rocket launch to prevent a meltdown. NASA and DARPA plan to mitigate the risk of a nuclear accident by activating the reactor only in orbit.

Cooperation and political framework

The MPD thruster project is led by JPL, has been running for about two and a half years, and is being carried out in cooperation with Princeton University and NASA Glenn Research Center in Cleveland. The overarching nuclear propulsion program is coordinated by the Marshall Space Flight Center in Huntsville, Alabama, as part of NASA's Space Technology Mission Directorate.

NASA Administrator Isaacman used the test report for a politically charged statement: The test indicates that the US is on its way to landing an American astronaut on Mars. Isaacman has also recently attracted attention elsewhere. In a US Senate budget hearing on April 28, 2026, he advocated for Pluto to be declared a planet again. Such announcements are not uncommon in NASA's communication; the agency largely leaves open how far the path from a successful lab test to a manned Mars mission actually is.

(vza)