Lab instrument now on two-billion-mile journey to the metallic asteroid Psyche

An instrument designed and built by Lawrence Livermore National Laboratory (LLNL) researchers departed Earth last week on a two-billion-mile, nearly six-year journey through space to explore a rare, largely metal asteroid.

The Livermore high-purity germanium (HPGe) gamma-ray sensor is an essential part of a larger gamma-ray spectrometer (GRS) built in collaboration with researchers from Johns Hopkins Applied Physics Laboratory (JHAPL) in Laurel, Maryland. It is part of a suite of instruments set to make the first-ever visit to Psyche, the largest metal asteroid in the solar system. The Psyche mission is led by Arizona State University (ASU).

A SpaceX Falcon Heavy rocket carrying NASA’s Psyche spacecraft lifted off from the Kennedy Space Center.

“Psyche is scientifically interesting because it is thought to be a planetary core, a remnant of a collision during the early stages of the development of the solar system,” said LLNL physicist Morgan Burks, who heads the Lab team. “We believe that exploration of the Psyche asteroid could increase our understanding of the hidden cores of Earth, Mars, Mercury and Venus.”

Psyche mission principal investigator Lindy Elkins-Tanton of ASU noted that the exploration of Psyche will permit scientists to “literally visit a planetary core — the only way humankind ever can.”
    
Lab scientists worked with collaborators from the JHAPL to combine the Lab HPGe gamma-ray sensor into the GRS and integrate it with additional components for the spaceflight mission.

More gamma-ray spectrometers coming

The LLNL instrument is the second HPGe gamma-ray sensor designed and built by LLNL for space exploration within the past nearly 20 years. Two more such sensors are now being designed and built by LLNL researchers for future space exploration missions.

“In collaboration with Johns Hopkins APL, we’ve become the world experts in gamma-ray spectroscopy for planetary science,” Burks said. “We are helping to open up a new era in nuclear spectroscopy for space applications.”

Burks called the launch one of the highlights of his 21-year Lab career.

“This is an instrument for which I’ve led the design in collaboration with our LLNL team and the Johns Hopkins APL. We have the chance to see it launch to the asteroid belt and our team will get to use the scientific data to better understand this rare metallic asteroid,” he said.

LLNL’s gamma-ray sensor is part of the Psyche spacecraft’s larger gamma-ray spectrometer that also includes a cryocooler, an anti-coincidence sensor, a data-processing unit and flight software programming.

Psyche may be composed largely of iron and nickel, similar to the Earth’s core. The study of this asteroid could help researchers better understand the formation of planetary cores, including Earth.

Asteroids are rocky space bodies that orbit around the sun and range in size from tiny dust particles to upward of 600 miles in diameter. Named for the Greek goddess of the soul, Psyche resides in the asteroid belt between Mars and Jupiter. This belt is home to more than 1 million other asteroids larger than a half-mile in diameter, along with many smaller ones, according to NASA estimates.

Determining the asteroid’s elemental composition

The Lab’s Psyche GRS, about the size of a loaf of bread and weighing four to five pounds, will determine the elemental composition of the asteroid’s surface. Although the asteroid is believed to be primarily composed of iron and nickel, other elements of interest include silicon, potassium, sulfur, aluminum, calcium, thorium and uranium.

“Psyche’s surface releases a large number of gamma rays that are induced by cosmic ray bombardment,” Burks said. “By measuring the energy of the gamma rays with high resolution, it is possible to determine the composition of the planet's surface. Each element gives off a unique gamma ray signature.”

Burks’s LLNL Psyche team includes nuclear engineer Nathan Hines, physicist Geon-bo Kim and former Lab nuclear engineer Lena Heffern, who now works at the University of Colorado Laboratory for Atmospheric and Space Physics. The team has been assisted by Livermore-based Pegasus Design, a mechanical design firm.

In 2004, NASA’s MESSENGER (short for MErcury Surface, Space ENvironment, GEochemistry and Ranging) spacecraft, also built and operated at Johns Hopkins APL, was launched toward Mercury with a suite of seven instruments, including an LLNL-developed HPGe gamma-ray sensor.

The MESSENGER GRS and other instruments journeyed through the hostile environment of space to the innermost planet in the solar system for about 6.5 years over more than 4.8 billion miles.

Once there, the MESSENGER GRS took measurements in the harsh thermal environment around Mercury, where the sun is 11 times brighter than on Earth and the surface temperature can reach 400 degrees Celsius (752 degrees Fahrenheit).

“The Psyche mission benefits from years of research and development from the MESSENGER project and other Lab GRS instruments. In effect, we’re leveraging the R&D that we achieved during the MESSENGER preparation and flight,” Burks said.

The Psyche GRS will be the fourth generation of high-purity, germanium-based gamma ray spectrometers, following the Cryo-3, the MESSENGER GRS and the GeMini.

Officially known as 16 Psyche (the number designates the order in which it was discovered), the asteroid was first found in 1852 by an Italian astronomer. Some 130 miles (or 210 kilometers) in diameter, it is one of the 10 most massive asteroids in the asteroid belt.

To reach the asteroid, the Psyche spacecraft will travel about 2.2 billion miles over a nearly six-year period. The trip will include flying near Mars in May 2026 for what’s called a gravity assist. Harnessing Mars’ gravity, Psyche will increase its speed and change direction without using much propellant. The spacecraft will arrive at Psyche in August 2029 and continue orbiting for at least 26 months. Psyche will eventually come within 47 miles (or 75 kilometers) of the asteroid’s surface.

Burks and his team are currently designing and building gamma-ray spectrometers for two future space missions: one to the moons of Mars and the other to the largest moon of Saturn.

The team is building a gamma-ray sensor for the Japanese aerospace exploration agency, JAXA, which will launch a mission in October 2024 to study the moons of Mars and land on Phobos, one of Mars’s moons.

In addition, they are designing a gamma-ray sensor for a NASA mission called Dragonfly, a rotorcraft lander set for launch around 2027. It will explore Titan, the largest moon of Saturn.