NASA takes step toward ion engines powered by fission reactors

A new prototype ion engine known as a lithium-fed magnetoplasmadynamic (MPD) thruster has passed a crucial test at NASA. The space agency is hoping to eventually combine this technology with nuclear fission to produce power and thrust for lengthy space flights, such as a crewed mission to Mars.

Ion propulsion: An ion engine generates thrust by using an electromagnetic field to accelerate ions (electrically charged atoms) through a nozzle. This process is referred to as electric propulsion or ion propulsion. Such engines are capable of achieving high velocities while using 90 percent less propellant than chemical-burning engines and can also reduce the mass of spacecraft.

NASA began using ion engines for some space missions during the 1960s. In 1998, the agency's launch of the Deep Space 1 mission, which flew past the asteroid 9660 Braille, marked the first time that such technology was used for missions beyond Earth orbit. Ion engines were used in several subsequent robotic space missions by NASA, the European Space Agency, and other countries. The most powerful ion engine that is currently deployed by NASA is on the Psyche mission, which was launched in 2023 to arrive at the asteroid 16 Psyche in 2029. That engine can produce velocities up to 124,000 miles (200,000 kilometers) per hour.

25 times more powerful: The newly tested MPD thruster is reportedly 25 times more powerful than the engine on the Psyche spacecraft. NASA administrator Jared Isaacman said in a recent statement, "This marks the first time in the United States that an electric propulsion system has operated at power levels this high, reaching up to 120 kilowatts. We will continue to make strategic investments that will propel that next giant leap."

Unlike a typical ion engine, which uses xenon gas as the ion source, the prototype MPD thruster generates strong electrical currents that interact with a magnetic field to accelerate lithium ions. In five test firings conducted in February inside the Condensable Metal propellant (Comet) vacuum facility at NASA's Jet Propulsion Laboratory, this thruster reached the 120-kW power level. These first test firings of the prototype engine were deemed a success.

JPL senior research scientist James Polk said, "Designing and building these thrusters over the past couple of years has been a long lead-up to this first test. It's a huge moment for us because we not only showed that the thruster works, but we also hit the power levels that we were targeting. And we know we have a good testbed to begin addressing the challenges to scaling up."

The next target for Polk and his team at JPL is to produce power levels between 500 kW and 1 MW with an ion engine. Once that target is achieved, hopefully within the next few years, the researchers intend to shoot for a power level of 4 MW.

Combining ion thrust with fission power: The ultimate goal of this NASA/JPL research is to develop a spacecraft using several such engines to carry astronauts to Mars. Instead of using solar arrays to generate power for the ion engines (as has been done with such engines in the past), NASA's ideal ion engine would be powered by a small nuclear fission reactor, which would theoretically be able to produce more power than solar panels.

The concept of using a fission reactor to power an ion engine is slated to be tested soon by NASA's Space Reactor-1 Freedom project. In that project, which is scheduled to be launched by the end of 2028, a spacecraft with a xenon-fueled ion engine powered by a fission reactor will carry a group of miniature rotorcraft to Mars.

Additional ideas and plans for the use of nuclear power in space missions were described in a White House Office of Science and Technology Policy memorandum that was released in April.