NASA recently successfully tested an experimental plasma thruster powered by lithium, marking an important step forward for human Mars missions. Engineers at NASA's Jet Propulsion Laboratory (JPL) in Southern California fired up the electromagnetic engine, allowing it to reach power levels never achieved by this type of propulsion system in the United States.
The test was conducted on February 24 in JPL’s vacuum chamber dedicated to high-power electric propulsion research. During testing, the prototype engine operated with more power than any electric thruster on any NASA flying spacecraft. The researchers say the results will provide guidance for the next phase of development and testing.
NASA Administrator Jared Isaacman said: "At NASA, we are doing many things at once, but we have never lost sight of Mars. Our thruster's successful performance in this test demonstrates the substantial progress made in sending American astronauts to the Red Planet. This is the first time the United States has an electric propulsion system operating at such a high power level, reaching 120 kilowatts. We will continue to make strategic investments to promote the next giant leap."
The engine uses lithium metal vapor and belongs to the Magneto-Plasma Dynamics (MPD) thruster technology category. Such systems generate thrust by using electric currents and magnetic fields to accelerate plasma at extremely high speeds. During five separate firing tests, the thruster's tungsten electrodes glowed bright white and temperatures climbed to more than 5,000 degrees Fahrenheit (2,800 degrees Celsius). The testing was conducted at JPL's Electric Propulsion Laboratory, which has a unique facility capable of safely evaluating electric thrusters that rely on metallic vapor propellants with power in the megawatt range.
The fuel efficiency of electric propulsion systems is much higher than that of traditional chemical rockets, and propellant usage can be reduced by up to 90%. Instead of delivering strong thrust for short periods of time, they provide gentle but sustained thrust that steadily accelerates the spacecraft over long periods of time. NASA already uses electric propulsion technology on missions such as Psyche, which currently runs the agency's most powerful electric thrusters. Over time, Psyche's propulsion system can accelerate the spacecraft to 124,000 miles per hour.
This new lithium-powered MPD thruster could eventually provide significantly more thrust than existing systems. Although scientists have been studying MPD propulsion technology since the 1960s, the technology has never been used in practical applications in space. In recent tests at JPL, the engine reached a power of 120 kilowatts, which is more than 25 times the power of the flight thrusters on the "Spirit Star".
"The past several years of designing and building these thrusters have been a long-term preparation for this first test," said James Polk, senior research scientist at JPL. "This is an important moment for us because we not only demonstrated the thrusters' ability to work, but also achieved our target power levels. We know we have a good test platform to start solving the challenges of scaling up."
Polk observed the experiment through a small viewing window in the 26-foot-long (8-meter-long) water-cooled vacuum chamber. When the thruster activates, its nozzle-like outer electrode glows intensely, creating a bright red plasma plume. Polk has worked in the field of electric propulsion technology for decades, having contributed to NASA's Dawn mission and Deep Space One, the first spacecraft to demonstrate electric propulsion technology beyond Earth orbit.
The researchers hope to eventually increase the power output of each thruster to between 500 kilowatts and 1 megawatt. One of the biggest technical challenges is ensuring that the hardware can withstand long-term operation in extreme temperatures. A manned mission to Mars may require a total of 2 to 4 megawatts of power, meaning several MPD thrusters may need to operate continuously for more than 23,000 hours.
Scientists believe that lithium-powered MPD engines may play an important role in future deep space exploration because they combine strong thrust with efficient propellant use. Paired with nuclear power systems, they can reduce launch mass while carrying the heavy payloads required for human missions to Mars.
The MPD thruster project has been in development for the past two and a half years, a collaboration between JPL, the Princeton Plasma Physics Laboratory in New Jersey, and NASA's Glenn Research Center in Cleveland. Funding comes from NASA's Space Nuclear Propulsion Program, which began in 2020 to support the development of megawatt-scale nuclear electric propulsion systems for future missions to Mars. The work is managed by NASA's Marshall Space Flight Center in Huntsville, Alabama, under NASA's Space Technology Mission Directorate.