NASA's Psyche spacecraft uses Mars flyby as rehearsal for asteroid encounter

Not quite halfway through a six-year sojourn through the Solar System, a NASA spacecraft used a close encounter with Mars last week as a dress rehearsal for its arrival at the Solar System’s largest metal asteroid in 2029.

The Psyche mission launched more than two-and-a-half years ago, in October 2023, from Kennedy Space Center, Florida, to kick off a journey of some 2.2 billion miles (3.6 billion km) to reach its unexplored namesake, the asteroid Psyche. The robotic research mission got an initial lift from a powerful SpaceX Falcon Heavy rocket. It uses plasma engines to gradually build up the impulse needed to reach its destination in the asteroid belt, between the orbits of Mars and Jupiter.

A flyby of Mars last Friday gave the spacecraft its most significant boost since launch. Navigators at NASA’s Jet Propulsion Laboratory in California set up the spacecraft for a course taking it 2,864 miles (4,609 km) from the Martian surface, well above the planet’s tenuous atmosphere. Psyche used Martian gravity like a slingshot to gain enough speed to reshape its orbit around the Sun, putting the probe on a path to intercept its asteroid target.

Right on the money

“Although we were confident in our calculations and flight plan, monitoring the DSN’s (Deep Space Network’s) Doppler signal in real time during the flyby was still exciting,” said Don Han, Psyche’s navigation lead at JPL, in a statement. “We’ve confirmed that Mars gave the spacecraft a 1,000-mile-per-hour boost and shifted its orbital plane by about 1 degree relative to the Sun. We are now on course for arrival at the asteroid Psyche in summer 2029.”

The gravity assist was the main goal of the Mars flyby, but ground teams used the encounter to test the spacecraft’s three science instruments: a multispectral imager consisting of two cameras, a gamma-ray and neutron spectrometer, and a magnetometer. Similar sensors are flying on other spacecraft that are permanently studying Mars, so the real benefit of running the instruments during Psyche’s encounter was for scientists to use the flyby as a practice run for when it reaches the asteroid Psyche.

“As a bonus, it captured Mars images from a rare perspective,” NASA said in a press release.

The spacecraft approached Mars from a high phase angle, or from the side opposite the Sun, making the planet appear as a thin crescent as Psyche moved in for the encounter. The wispiness of the thin Martian atmosphere was on full display, with sunlight shining through diffuse clouds of dust suspended dozens of miles over the sharp edge of the planet’s rust-colored surface.

As Psyche zoomed past the red planet, its cameras captured a wide-angle overhead view of Mars’ southern polar ice cap. Jim Bell, who leads the Psyche imager instrument team at Arizona State University, said the spacecraft took thousands of images during the encounter. The observations will help scientists “calibrate and characterize” the performance of the cameras, Bell said.

Psyche’s magnetometer may have detected a signature of the solar wind interacting with Mars’ upper atmosphere or its remnant magnetic field, and its spectrometers were tuned to measure the chemical composition of the Martian surface underneath the spacecraft’s flight path.

Numerous other missions are exploring Mars full-time, so there’s little chance of any major discoveries lurking in Psyche’s flyby datasets. But scientists should be able to calibrate the mission’s instruments by comparing flyby observations with archival data from other Mars missions.

It is always interesting to gain new perspectives, even on something familiar. You can’t see a crescent Mars from Earth. But the Psyche mission’s real payoff will come in three years, when the probe pulls in close to asteroid Psyche, an object the size of Massachusetts that is rich in iron, nickel, and likely other metals that we know only as a fuzzy blob through telescopes. It is truly uncharted territory, but the Psyche spacecraft will have more than two years to survey the asteroid, far longer than the fleeting glimpse it got of Mars last week.