Psyche Spacecraft Aces Mars Gravity Assist on Journey to Metal Asteroid

Successful Mars Flyby Propels Mission Forward

NASA's Psyche spacecraft completed its close approach of Mars on May 15, coming within 2,864 miles (4,609 kilometers) of the planet's surface. This flyby used a gravity assist from Mars to provide a critical boost in speed and to adjust the spacecraft's orbital plane without using any onboard propellant, sending it on its way toward the metal-rich asteroid Psyche. Mars gave the spacecraft a 1,000 mile‑per‑hour boost and shifted its orbital plane by about 1 degree relative to the Sun.

After the Mars flyby, the flight team analyzed radio signals between the spacecraft and NASA's Deep Space Network (DSN), the agency's global system for communicating with interplanetary spacecraft, to confirm that Psyche was on the correct trajectory. "Although we were confident in our calculations and flight plan, monitoring the DSN's Doppler signal in real time during the flyby was still exciting," said Don Han, Psyche's navigation lead at NASA's Jet Propulsion Laboratory in Southern California.

Launched on Oct. 13, 2023, the Psyche spacecraft relies on a solar-electric propulsion system and the inert gas xenon for propellant, gradually gaining speed over the course of its long journey. Psyche's mission planners are using the Mars flyby to save propellant, letting the planet's gravity do some of the work instead of the propulsion system alone.

Science Instruments Get Valuable Practice Run

In the days running up to and during close approach, all of Psyche's instruments were powered up for calibration efforts, including its imagers, magnetometers, and gamma-ray and neutron spectrometer. The planetary encounter provided the mission a valuable practice run for when it reaches the asteroid Psyche; as a bonus, it captured Mars images from a rare perspective.

The images will provide valuable data and help the team hone techniques they will need when the spacecraft approaches and begins orbiting the asteroid Psyche in late 2029. Early calibration measurements made by Psyche's magnetometers may have detected Mars' bow shock as the spacecraft passed the planet. The gamma-ray and neutron spectrometer team was also quickly gathering data to calibrate the instrument by comparing their measurements with the large pool of existing Mars data.

Bell also leads the Mastcam-Z imaging investigation on NASA's Perseverance Mars rover mission team, which was among several missions that provided complementary surface and atmospheric imaging as well as navigation data during the flyby to help with calibration efforts. Other missions involved include NASA's Mars Reconnaissance Orbiter, 2001 Mars Odyssey orbiter, and Curiosity rover, along with ESA's (European Space Agency's) Mars Express and ExoMars Trace Gas Orbiter.

Unique Views and Unexpected Discoveries

Psyche approached Mars from a high phase angle, meaning it looked like a thin crescent as the spacecraft approached. This representative color image, captured by Psyche's multispectral imager instrument, features the double-ring crater Huygens and the surrounding heavily cratered southern highlands. This is the first view of a nearly "full Mars" as seen by NASA's Psyche spacecraft shortly after its closest approach to the planet on May 15, 2026. The view extends from the south polar cap northwards to the Valles Marineris canyon system and beyond.

The team thinks that the Psyche probe may observe a faint dusty ring, or torus, around Mars, which is thought to exist as a result of tiny space rocks, or " micrometeorites," striking the surfaces of the planet's two moons, Phobos and Deimos, and ejecting dust particles into space. The imager will also capture "satellite search" observations of the space surrounding the planet — a practice run for when the team will be searching for any moonlets around the asteroid Psyche.

Journey to an Ancient World's Core

The spacecraft is now headed directly toward the asteroid, located in the main asteroid belt between Mars and Jupiter. When it arrives in August 2029, it will insert itself into orbit around the asteroid Psyche, which is thought to be the partial core of a planetesimal, a building block of an early planet. Through a series of circular orbits that go lower and then higher in altitude around Psyche, which is about 173 miles (280 kilometers) across at its widest point, the spacecraft will map the asteroid and gather science data.

If the asteroid proves to be the metallic core of an ancient planetesimal, it could offer a one-of-a-kind window into the interior of rocky planets like Earth.