A satellite company named Maxar recently delivered a piece of spacecraft the size of a passenger van to NASA’s Jet Propulsion Laboratory in California. This chassis will serve as the backbone of a robotic spaceship that will explore a metallic asteroid for the first time. This ambitious mission, named Psyche after the eponym asteroid it will explore, should be launched next summer on a Falcon Heavy rocket.
Once in space, the spacecraft will use an innovative means of propulsion, known as Hall thrusters, to reach the asteroid. It will be the first time that a spatialship ventured into deep space using Hall Effect thrusters. Without this technology, the Psyche mission likely wouldn’t happen – certainly not at its cost of just under $ 1 billion.
For David Oh, the large square frame represents one of those “full circle” moments in life. Over two decades ago, he worked on Hall Effect thruster technology as a graduate student at the Massachusetts Institute of Technology. He then worked for Space Systems / Loral, which first put the propulsion technology on large commercial satellites and would later be acquired by Maxar.
After working on the first commercial satellite launches powered by Hall Effect thrusters, Oh left the private sector in 2003 to join NASA’s Jet Propulsion Laboratory, where he has since worked on a number of missions, including the flight Curiosity at red planet in 2011. He is now technical manager of the Psyche mission.
“I have been working on electric propulsion for over two decades,” he said in an interview.
And now the Hall thruster technology that Oh worked on as a graduate student will take NASA in an entirely new place: Psyche. No spacecraft has ever visited a world like this, made up of around 60% metal. We are correct no idea what it will look like.
Chemical propulsion powered engines are perfect for launching rockets off the Earth’s surface when you need a powerful blast of energy to break out of the planet’s gravitational well. But chemical rocket engines aren’t the most fuel-efficient machines in the world because they absorb the propellant. And once a spaceship is in space, there are more fuel-efficient means of travel.
One of these is solar-electric propulsion, which uses solar panels to capture energy from the Sun, which in turn ionizes and accelerates a gas – usually xenon – to produce thrust. It’s not really a push. In fact, it’s exceptionally light. Each of the boosters in the Psyche mission reaches at most roughly the same force as that exerted by two or three quarters in the palm of the hand. But because they’re so fuel efficient, solar-electric thrusters don’t burn for a few minutes at a time. They burn for months, producing a steady acceleration.
NASA has been experimenting with this technology for some time. The space agency first tested electric propulsion technology in its Deep Space 1 mission, which was launched in 1998, and then in the Dawn mission in 2007 which visited Vesta and Ceres in the asteroid belt.
These spacecraft used ion thrusters. Hall-effect thrusters, on the other hand, use a simpler design, with a magnetic field to confine the thruster flow. These thrusters were invented in the Soviet Union and later adapted for commercial use by Maxar and other companies. Today, many of the larger communications satellites in geostationary orbit, such as those that deliver DirecTV, use Hall-effect thrusters to maintain the station.
But now, for the first time, they are being used for a deep space mission. NASA and Maxar believe the technology is ready, but it has yet to be proven in a new environment.
“It’s always a big deal when you go beyond Earth’s orbit,” said Robert Curbeam, a former astronaut who is senior vice president at Maxar. “As you move away from the Sun, you will generate less energy from solar panels. The radiation environment is going to be different. And there is the question of whether we can keep these thrusters pulsing for that long.