A new record for electric propulsion in the United States now stands at 120 kilowatts. NASA engineers set it recently during a test of a thruster that burns lithium metal vapor, and the agency’s people think it could one day help carry astronauts to Mars.
The figure is estimated at 25 times the power of the thrusters on NASA’s Psyche spacecraft, which is headed for asteroid 16 Psyche and carries what are described as the most powerful electric thrusters ever built. Psyche is cruising at roughly 135,000 kph (84,000 mph). Near the end of its trip it should reach about 200,000 kph (124,000 mph). Electric systems build speed slowly while running continuously, and they use up to 90 percent less fuel than the chemical rockets now in service.
“Designing and building these thrusters over the last couple of years has been a long lead-up to this first test,” said James Polk, a senior research scientist at NASA’s Jet Propulsion Laboratory. “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.”
Why Mars needs so much more
A record at 120 kilowatts is still a long way from what a crewed flight would require. NASA estimates that a human Mars mission would call for 2 to 4 megawatts, spread across several thrusters, with more than 23,000 hours of operation. That works out to 958 days, or 2.6 years.
The thrusters would also have to survive heat above 2,800 degrees Celsius (5,000 degrees Fahrenheit). They reached that level in this test.
The long run time follows from the shape of the trip. Mars launch windows open only once every two years because of how the two planets orbit. Robotic spacecraft have usually taken about 6 to 7 months to arrive. A human mission would need a far larger ship for people, food, fuel and water. The approximate plan is 6 to 9 months out, about 18 months on the surface until the next window opens, and another 6 to 9 months home.
Less fuel could change that schedule, in principle. Whether lithium thrusters deliver on that is a question for the tests ahead.
