On a multi-billion-mile journey to the asteroid Psyche, a gamma-ray sensor developed by a team at Lawrence Livermore National Laboratory (LLNL) took its first measurements of a planetary surface after 2.6 years in deep space. NASA's Psyche spacecraft flew behind Mars for a gravity assist, with the red planet's gravitational field acting as a slingshot to change the flight path and increase the velocity of the spacecraft.
The sensor is part of the mission's gamma-ray spectrometer built in partnership with Johns Hopkins Applied Physics Laboratory. The instrument will allow researchers to examine the surface composition of the large, metal asteroid Psyche to better understand the inner core of rocky planets, like Earth.
Ahead of the Mars approach, the spacecraft powered on a suite of instruments for the rare opportunity to gather measurements and determine sensitivity as well as verify radiation damage and perform repair operations.
"The most exciting moment of the Mars gravity assist was when the whole team gathered online to watch a live feed of the Doppler tracking data from the spacecraft," said Morgan Burks, LLNL physicist. "But then I hardly slept waiting for the data to downlink from the spacecraft. It arrived in bits and pieces over the next several days, at all hours, and I was often up at 3 a.m. looking at fresh spectroscopy data."
The spectrometer collected gamma ray measurements as the spacecraft flew past Mars at over 12,000 miles per hour within 2,864 miles of the planet's surface. Despite exposure to galactic cosmic rays, solar storms and other radiation hazards of deep space, the instrument maintained its high resolution and performed as expected.
The team at LLNL also used the instrument's anti-coincidence shield to measure cosmic-ray rates, which help scientists interpret the gamma-ray data.
"The value of the spectroscopy data was not so much what it told us about Mars, as we spent less than two hours in close proximity to the planet," said Burks. "Rather, it was an invaluable dress rehearsal for when we arrive at the asteroid Psyche. We were able to test all aspects of the instrument performance and data pipeline."
Burks said that the flyby gave the researchers a lot of confidence that the instrument was performing well in the deep-space environment. The data will help gauge the sensor's sensitivity to elements expected at Psyche, including iron, nickel, silicon and sulfur. Those measurements will matter when the spacecraft reaches the asteroid and begins its science campaign.
Psyche's scientific appeal lies in its unusual makeup. Researchers believe the asteroid may be composed of metals from the core of a planetesimal, a building block of our solar system. As the first mission to Psyche, spectroscopy data will help unlock insights into planetary formation.
The team is already planning the next phase of the mission, with periodic systems checks scheduled every six months as the spacecraft continues towards the asteroid belt. The Psyche spacecraft is expected to arrive at the asteroid in August 2029 and orbit it for at least 26 months.
For now, the Mars gravity assist has given the LLNL team what it wanted most: a successful rehearsal for the long mission ahead.
The Psyche mission is led by Arizona State University in Tempe. Lindy Elkins-Tanton, at the University of California, Berkeley, is Psyche's principal investigator. NASA's Jet Propulsion Laboratory in Southern California is responsible for the mission's overall management, system engineering, integration and testing and mission operations.
