OSIRIS-REx probe touches down to grab bits of an asteroid, with assist from Aerojet

Alan Boyle
·5-min read
OSIRIS-REx probe
An artist’s conception shows NASA’s OSIRIS-REx probe lowering its sample collection arm to the surface of the asteroid Bennu. (Lockheed Martin Illustration)

NASA’s OSIRIS-REx probe reached the climax of its seven-year round trip to deep space today and briefly touched down on a near-Earth asteroid, propelled by thrusters made in the Seattle area.

Scientists and engineers at Lockheed Martin’s Mission Support Area in Colorado received word at 4:12 p.m. MT (3:12 p.m. PT) that the touch-and-go maneuver at asteroid Bennu was successful, sparking cheers and fist-shaking. The maneuver was aimed at collecting samples of dust and gravel on the asteroid’s surface.

Mission team members wore masks and tried to observe social distancing as a COVID-19 safety measure, but some hugged nevertheless.

“I can’t believe we actually pulled this off,” said the University of Arizona’s Dante Lauretta, principal investigator for the mission. “The spacecraft did everything it was supposed to do.”

All 28 of the rocket engines on the van-sized OSIRIS-REx probe were built at Aerojet Rocketdyne’s facility in Redmond, Wash., and provided to Lockheed Martin, the spacecraft’s main contractor.

“The sample collection portion of the mission requires our engines to perform with extremely high precision, with no room for error,” Aerojet Rocketdyne’s CEO and president, Eileen Drake, said in a pre-touchdown news release.

Fred Wilson, the head of business development for space systems at Aerojet Rocketdyne Redmond, said there was “a lot of excitement” at the Seattle-area facility when the crucial maneuver took place.

“These engines that we built roughly six years ago and shipped off … they’re doing their job out there,” Wilson told GeekWire after the encounter.

The touch-and-go maneuver, nicknamed TAG, targeted a 14-meter-wide (45-foot-wide) patch of the surface of Bennu, more than 200 million miles away from Earth. It took 18 and a half minutes for signals sent by the spacecraft to reach Earth — which meant that the descent had to be controlled autonomously, based on an analysis of close-up imagery conducted by the spacecraft’s onboard computer.

Just before the TAG took place, controllers reported that the spacecraft appeared to be within 1.7 meters (5.5 feet) of the target point. That was important, because the target site — nicknamed Nightingale — was carefully chosen to avoid rocky hazards on the surface.

When OSIRIS-REx was launched, back in 2016, mission planners had expected to find a smooth stretch of cosmic sand for sample collection. But after the probe’s arrival at Bennu in 2018, they were surprised to find that the surface was more rugged than they expected. That added to the pressure to execute a precision maneuver.

The OSIRIS-REx team took it slow and steady, sending commands that took the spacecraft through a four-hour descent sequence. Toward the end, the distance decreased at a rate of 4 inches (10 centimeters) per second, or less than a tenth of walking speed.

Beth Buck, mission operations program manager for Lockheed Martin, said the experience wasn’t anything like the “seven minutes of terror” that precede a Mars landing. “This is much more of a four and a half hours of mild anxiousness,” Buck quipped during a pre-touchdown briefing.

At the climax, OSIRIS-REx’s collection arm touched Bennu’s surface for only a few seconds. Compressed nitrogen gas was puffed into a contraption at the end of the arm that served as a sort of “reverse vacuum cleaner.” The puffs were designed to blow bits of material as big as pieces of gravel (about an inch wide) into a sample-collecting receptacle.

After the touch-and-go, the spacecraft immediately backed away for safety’s sake.

There was a lot riding on a successful maneuver: OSIRIS-REx has been studying Bennu for two years using a suite of scientific instruments, but collecting at least 2 ounces (60 grams) of material for return to Earth is the primary task for the $800 million mission.

OSIRIS-REx is an Egyptian-sounding acronym that stands for “Origins, Spectral Interpretation, Resource Identification, Security – Regolith Explorer.”

The 1,500-foot-wide asteroid is thought to be one of the leftovers from the formation of the solar system more than 4 billion years ago. It’s rich in water as well as in carbon-bearing compounds that are essential to organic processes. For those reasons, scientists hope that a close analysis of the samples, conducted with all the instruments available back on Earth, will yield fresh insights into planetary origins and the chemical precursors of life.

Scientists could also learn more about the types of resources that could be extracted from asteroids, as well as the best strategies for diverting potentially hazardous space rocks. Bennu itself has an ever-so-slight, 1-in-2,700 chance of colliding with Earth sometime between the year 2175 and 2199.

Detailed data from today’s encounter will be transmitted to Earth overnight and released during a news conference on Wednesday. If, for some reason, the collection effort didn’t actually pick up enough of a sample, the OSIRIS-REx team can try again in January.

If all goes according to plan, the spacecraft will begin the homeward journey next March, powered once again by Aerojet engines. In 2023, it’s due to fly past Earth and eject a capsule containing the precious sample for a parachute-aided descent to a recovery site in the Utah desert.

This is the first-ever asteroid sample return mission for NASA, following a precedent set by Japan more than a decade ago with its Hayabusa mission to the asteroid Itokawa. A follow-up probe, Hayabusa 2, is due to bring a sample from the asteroid Ryugu back to Earth in December.

Still more asteroid missions are planned in the years ahead. NASA is scheduled to launch the Lucy probe on an asteroid tour next year, followed by the start of the Psyche spacecraft’s journey to a metal-rich asteroid of the same name in 2022.

Cosmic Log update: OSIRIS-REx is overflowing with asteroid stuff

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