NASA Fires Up Powerful Lithium-Fed Thruster for Trips to Mars

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A novel electromagnetic thruster passed an initial test in a specialized chamber at JPL. With further development, these thrusters could support human missions to the Red Planet.

A technology that could propel crewed missions to Mars and robotic spacecraft throughout the solar system was recently put to the test at NASA’s Jet Propulsion Laboratory in Southern California. On Feb. 24, for the first time in years and at power levels exceeding any previous test in the United States, a team fired up an electromagnetic thruster that runs on lithium metal vapor.

This prototype achieved power levels beyond the highest-power electric thrusters on any of the agency’s current spacecraft. Valuable data from the first firing of this thruster will help inform an upcoming series of tests.

“At NASA, we work on many things at once, and we haven’t lost sight of Mars. The successful performance of our thruster in this test demonstrates real progress toward sending an American astronaut to set foot on the Red Planet,” said NASA Administrator Jared Isaacman. “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.”

During five ignitions, the tungsten electrode at the thruster’s center glowed bright white, reaching over 5,000 degrees Fahrenheit (2,800 degrees Celsius). The work was conducted in JPL’s Electric Propulsion Lab, home to the condensable metal propellant vacuum facility, a unique national asset for safely testing electric thrusters that use metal vapor propellants at up to megawatt-class power levels.

Powering up

Electric propulsion uses up to 90% less propellant than traditional, high-thrust chemical rockets. Current electric propulsion thrusters, like those powering NASA’s Psyche mission, use solar power to accelerate propellants, producing a low, continuous thrust that reaches high speeds over time. NASA JPL is testing a lithium-fed magnetoplasmadynamic (MPD) thruster, a technology that has been researched since the 1960s but never flown operationally. The MPD engine differs from existing thrusters by using high currents interacting with a magnetic field to electromagnetically accelerate lithium plasma.

During the test, the team achieved power levels of up to 120 kilowatts. That’s over 25 times the power of the thrusters on Psyche, which is currently operating the highest-power electric thrusters of any NASA spacecraft. In the vacuum of space, the gentle but steady force Psyche’s thrusters provide over time accelerates the spacecraft to 124,000 mph.

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

To view the test, Polk peered through a small portal into the 26-foot-long (8-meter-long) water-cooled vacuum chamber. Inside, the thruster flared to life, its nozzle-shaped outer electrode glowing incandescent as it emitted a vibrant red plume. Polk has researched lithium-fed MPD thrusters for decades, having worked on NASA’s Dawn mission and the agency’s Deep Space 1, the first demonstration of electric propulsion beyond Earth orbit.

The team aims to reach power levels between 500 kilowatts and 1 megawatt per thruster in coming years. Because the hardware operates at such high temperatures, proving the components can withstand the heat over many hours of testing will be a key challenge. A human mission to Mars might need 2 to 4 megawatts of power, requiring multiple MPD thrusters, which would have to operate for more than 23,000 hours.

Lithium-fed MPD thrusters have the potential to operate at high power levels, use propellant efficiently, and provide significantly greater thrust than currently flying electric thrusters. Fully developed and paired with a nuclear power source, they could reduce launch mass and support payloads required for human Mars missions.

The MPD thruster work, in development for the past 2½ years, is led by JPL in collaboration with Princeton University in New Jersey and NASA’s Glenn Research Center in Cleveland. It is funded by NASA’s Space Nuclear Propulsion project, which in 2020 began supporting a megawatt-class nuclear electric propulsion program for human Mars missions by focusing on five critical technology elements, of which the electric propulsion subsystem is one. The project, based at the agency’s Marshall Space Flight Center in Huntsville, Alabama, is part of the NASA’s Space Technology Mission Directorate.