Summary
NASA says the Psyche spacecraft began using its solar-powered thrusters nearly 90% of the time after a Mars gravity assist. The extended thrusting is intended to keep it on course for an asteroid rendezvous in summer 2029.
NASA’s Psyche spacecraft began using its solar-electric propulsion system nearly continuously on Sept. 28, after a Mars gravity assist. The thrusters are expected to operate for nearly 90% of the time available until the spacecraft reaches asteroid Psyche in summer 2029, with pauses for engineering tasks and a weekly check-in with mission controllers.
The mission launched in October 2023. During its first journey leg, it used propulsion intermittently to reach the right position for Mars to alter its trajectory and provide a speed boost without using propellant for that manoeuvre. NASA says the current thrusting plan keeps the spacecraft on track for its asteroid rendezvous.
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How the propulsion system builds speed
Psyche’s Hall-effect thrusters use electromagnetic fields to expel charged xenon atoms, or ions, and generate thrust. The spacecraft has four thrusters, which operate one at a time. Each can produce up to 250 millinewtons of force—roughly the force of holding an AA battery—but that gentle push accumulates over a long journey through space.
The thrusters draw electricity from two five-panel solar arrays. Together, the arrays have a sunlight-collecting area of 800 square feet (75 square metres). Psyche launched with nearly 2,400 pounds (1,090 kilograms) of xenon in seven tanks. NASA reports that the spacecraft has used about one-third of its supply in the three years since launch, leaving propellant for the journey and its planned two-year prime science mission around the asteroid.
The mission plans to thrust at full power for three months from the start of this operating phase, then gradually reduce to about half power as the spacecraft moves farther from the Sun and its arrays receive less sunlight. At its maximum speed during cruise, NASA says Psyche will travel at more than 100,000 mph (160,900 kph) relative to an observer on Earth.
Managing a small twisting force
The Hall thrusters’ operation also creates a subtle navigation challenge. As xenon ions swirl in the thruster’s magnetic field and leave the spacecraft, they can produce a slight torque—a twisting force that could affect the spacecraft’s pointing if left uncorrected.
Psyche uses reaction wheels to absorb the resulting angular momentum. After several hours, engineers switch off the operating thruster, rotate the spacecraft and briefly run another thruster at low power in a different direction. NASA says this manoeuvre helps remove momentum accumulated in the wheels.
The mission’s propulsion team has also been able to measure this torque in space over long periods and across different power levels and operating times. NASA describes Psyche as the first opportunity to make those measurements on a Hall thruster in this way.
What Psyche will investigate
On arrival, Psyche is planned to enter orbit around the asteroid, which is about 173 miles (280 kilometres) across at its widest point. The spacecraft will map it and collect science data from a series of orbits at progressively lower and then higher altitudes.
Psyche is thought to be the partial core of a planetesimal, a building block of an early planet. If that interpretation is correct, studying the asteroid could offer a view into the interiors of rocky planets. The mission’s measurements will help establish what this metal-rich object is like and what it can reveal about planetary formation.