Solar electric propulsion launches NASA’s Psyche spacecraft

When the time comes for NASA’s Psyche spacecraft to propel itself into deep space, it will be more the brain than the muscles that will do the work. Once a matter of science fiction, the efficient and quiet power of electric propulsion will provide the force that propels the Psyche spacecraft to the main asteroid belt between Mars and Jupiter. The orbiter’s target: a metal-rich asteroid also called Psyche.

The spacecraft will launch in August 2022 and will travel approximately 1.5 billion miles (2.4 billion kilometers) over three and a half years to get to the asteroid, which scientists believe may be part of the core of ‘a planetesimal, the cornerstone of the first rock planet. Once in orbit, the mission team will use the payload of scientific instruments to investigate what this single target may reveal about the formation of rocky planets like Earth.

The spacecraft will rely on the Falcon Heavy launcher’s large chemical rocket engines to lift off the launch pad and escape Earth’s gravity. But the rest of the trip, once Psyche separates from the launcher, will rely on solar electric propulsion. This form of propulsion begins with large solar panels that convert sunlight into electricity, providing the power source for the spacecraft’s thrusters. They are known as Hall thrusters, and the Psyche spacecraft will be the first to use them beyond our moon’s orbit.

For the thruster, Psyche will carry tanks full of xenon, the same neutral gas used in car headlights and plasma TVs. The spacecraft’s four thrusters will use electromagnetic fields to accelerate and expel the charged atoms, or ions, from this xenon. When these ions are expelled, they create a thrust that gently propels Psyche into space, emitting blue beams of ionized xenon.

In fact, the push is so gentle that it exerts about the same pressure you would feel when holding three-quarters in your hand. But that’s enough to speed Psyche into deep space. Without atmospheric drag to hold it back, the spacecraft will eventually accelerate to speeds of up to 200,000 miles per hour (320,000 kilometers per hour).

Because they are so efficient, Psyche’s Hall thrusters could run almost non-stop for years without running out of fuel. Psyche will transport 2,030 pounds (922 kilograms) of xenon in its tanks; engineers estimate the mission would burn about five times as much propellant if it were to use traditional chemical propellants.

“Even at the beginning, when we first designed the mission in 2012, we were talking about solar electric propulsion as part of the plan. Without it, we wouldn’t have the Psyche mission, ”said Lindy Elkins-Tanton of Arizona State University. , who as principal investigator leads the mission. “And that’s part of the character of the mission. It takes a specialized team to calculate trajectories and orbits using solar electric propulsion.”

A gentle maneuver

Psyche will be launched from the historic Pad 39A at NASA’s Kennedy Space Center. The Falcon Heavy will put the spacecraft on a path to fly through Mars for gravitational assistance seven months later, in May 2023. In early 2026, the thrusters will do the delicate work of putting the spacecraft into orbit around the asteroid. Psyche, using a little ballet to get back into orbit around his target.

This task will be particularly tricky due to the scant knowledge scientists have about the asteroid, which only appears as a tiny dot of light in telescopes. Ground-based radar suggests it’s about 226 kilometers wide and shaped like a potato, meaning scientists won’t know until they get there how exactly its works. gravity field. As the mission conducts its 21-month scientific investigation, the navigation engineers will use the electrically powered thrusters to fly the spacecraft through a progression of orbiting that will gradually bring the spacecraft closer to Psyche.

NASA’s Jet Propulsion Laboratory in Southern California, which manages the mission, used a similar propulsion system with the agency’s Deep Space 1, which was launched in 1998 and flew over an asteroid and a comet before the mission ended in 2001. Next came Dawn, who used solar electric propulsion to orbit the asteroid Vesta and then the protoplanet Ceres. The first spacecraft to orbit two alien targets, the Dawn mission lasted for 11 years, ending in 2018 when it used the last hydrazine thruster used to maintain its focus.

Propulsion partners

Maxar Technologies has used solar electric propulsion to power commercial communications satellites for decades. But for Psyche, they needed to adapt the super efficient Hall thrusters to fly into deep space, and that’s where the engineers at JPL came in. Both teams hope Psyche, using Hall thrusters for the first time beyond lunar orbit, will help push the limits of solar electric propulsion.

“Solar electric propulsion technology offers the right combination of cost savings, efficiency and power and could play an important role in supporting future scientific missions to Mars and beyond,” said Steven Scott, Manager of the Psyche de Maxar program.

In addition to supplying the thrusters, the Maxar team in Palo Alto, Calif., Was responsible for building the spaceship’s van-sized chassis, which houses the electrical system, the propulsion systems, the system. thermal and the guidance and navigation system. When fully assembled, Psyche will move into JPL’s huge thermal vacuum chamber for tests simulating the deep space environment. By next spring, the spacecraft will be shipped from JPL to Cape Canaveral for launch.