NASA’s most metallic mission to test new, higher-powered electric thrusters


A satellite company called Maxar recently delivered a piece of a 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 spacecraft exploring a metallic asteroid for the first time. This ambitious mission, named Psyche after the eponymous asteroid it will explore, will launch 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. This will be the first time a spacecraft has ventured into deep space using Hall thrusters, and without this technology, the Psyche mission probably wouldn’t be happening, certainly not at its cost of just under $ 1 billion.

For David Oh, the big, boxy chassis represents one of those “full circle” moments in life. More than two decades ago, he worked at Thruster Technology Hall as a graduate student at the Massachusetts Institute of Technology. He would continue to work 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 thrusters, Oh left the private sector in 2003 to come to NASA’s Jet Propulsion Laboratory, where he has since worked on various missions, including the Curiosity flight. to the red planet in 2011. Now, he serves as technical leader for the Psyche mission.

“I have been working in electric propulsion for more than two decades,” he said in an interview.

And now, the Hall thruster technology that Oh worked on as a graduate student will take NASA to a whole new place, Psyche. No spacecraft has ever visited a world like this, made up of roughly 60 percent metal. We really have no idea how it will look.

Electric propulsion

Chemical propulsion-powered engines are great for pulling rockets off the Earth’s surface when it takes a strong blast of energy to get out of the planet’s gravitational well. But chemical rocket engines are not the most fuel-efficient machines in the world, since they consume propellant. And once a spacecraft is in space, there are more fuel-efficient means of getting around.

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, typically xenon, to produce thrust. It’s not a huge boost. In fact, it is exceptionally light. Each of the Psyche mission thrusters reaches a maximum of roughly the same force as that exerted by two or three-quarters in the palm of the hand. But because they are so fuel efficient, solar electric thrusters don’t burn for a few minutes at a time. They burn for months, producing a constant acceleration.

NASA has been experimenting with this technology for a while. The space agency first tested electric propulsion technology on its Deep Space 1 mission, which launched in 1998, and later with the Dawn mission in 2007 that visited Vesta and Ceres in the asteroid belt.

These ships used ion thrusters. Hall thrusters, by contrast, use a simpler design, with a magnetic field to limit propellant flow. These thrusters were invented in the Soviet Union and later adapted for commercial purposes by Maxar and other companies. Many of the largest communications satellites in geostationary orbit today, such as those broadcasting DirecTV, use Hall thrusters for station maintenance.

But now, for the first time, they are being used for a mission in deep space. NASA and Maxar believe the technology is ready, but it has yet to be tested in a new environment.

“It’s always a big problem to go beyond Earth orbit,” said Robert Curbeam, a former astronaut who is Maxar’s senior vice president. “As you move away from the Sun, you will generate less energy from the solar arrays. The radiation environment will be different. And there is the question of whether we can keep these thrusters pulsing for that long.”

The mission

If NASA had tried to develop the Psyche mission with chemical propulsion, it would have required about five times as much fuel. This volume would have caused Psyche to be even larger than the Cassini probe that NASA used to explore the Saturn system from 2004 to 2017, Oh said. The Cassini mission cost about $ 4 billion, the kind of budget NASA reserves only for the highest priority “flagship” missions. NASA only flies one or two of these per decade, and the scientists behind Psyche, led by Lindy Elkins-Tanton of Arizona State University, knew they weren’t going to get this designation.

The use of Hall thruster-based technology enabled mission scientists and engineers to design a smaller, more affordable spacecraft. Crucially, NASA was able to purchase a Maxar spacecraft chassis that was built largely from off-the-shelf technology. If NASA and the Jet Propulsion Laboratory had needed to develop this technology on their own, it would have cost billions of dollars and would have taken years longer.

Each of Psyche’s Hall thrusters will generate three times more thrust than the Dawn spacecraft’s ion thrusters and can process twice the power. This will allow the spacecraft to reach the asteroid Psyche, located in the main belt, in January 2026, after a 3.5-year journey.

Psyche is still a large spaceship, with large solar panels to collect sunlight in the asteroid belt.

POT

Instead of burning heavily as the spacecraft approaches Psyche, as is customary for a chemically powered vehicle, it will take a sip of xenon fuel and return to orbit around the asteroid. Over time, the spacecraft will get progressively closer, always trying to find a stable orbit around the asteroid, which has a strange shape and a non-uniform field of gravity. Having fuel efficient thrusters will help with this.

Finally, towards the end of this 21-month period, the spacecraft will reach about 100 km from the surface of Psyche, which has a diameter of about 220 km. In this lower orbit, Psyche will use a spectrometer to map the various elements that make up Psyche and answer the question of what exactly metallic asteroids are made of.

Oh said he was eager to find out if Psyche could be the core of something that could have become a planet during the early days of our Solar System, but it ultimately didn’t. If so, we could learn a lot more about the core of our own world, Earth. Furthermore, the findings from this mission will better inform scientists and entrepreneurs about the potential riches that could be derived from metallic asteroids, which could be critical to human settlements in deep space decades from now.

Image listing by NASA

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