OSIRIS-REx captures treasure trove of samples from asteroid Bennu

After OSIRIS-REx’s TAGSAM sample collector bumped into the soil of the asteroid Bennu, flight controllers repositioned the device to get a glimpse inside. They found it jam packed with small rocks and soil far in excess of the 60 grams required for mission success. Image: NASA/Goddard/University of Arizona

Scientists and engineers knew right away that the OSIRIS-REx spacecraft’s “TAGSAM” collector successful contacted the surface of asteroid Bennu on 20 October. But they didn’t know for sure what, if anything, had been captured until they got a chance to aim a camera into the mechanism’s interior two days later.

And they were thrilled by what they saw.

While 60 grams (2.12 ounces) was the minimum requirement for mission success, the photos revealed hundreds of grams of material in the 20 percent of the TAGSAM collector visible to the camera.

“Quite honestly, we could not have performed a better collection experiment,” said Dante Lauretta, the OSIRIS-REx principal investigator. “So with all of that underneath our belt at this point, I am highly confident that TAGSAM was successful, that had collected abundant mass, definitely evidence of hundreds of grams of material, and possibly more.”

So much, in fact, that at least one rock fragment could be seen lodged in a flap intended to trap collected particles inside an internal chamber. Instead, the camera views showed small rocks and particles working their way out of the collector and into open space.

OSIRIS-REx backs away from Bennu amid a blizzard of soil and small rocks after a blast of pressurized nitrogen gas stirred up material during a six-second touch-and-go sample collection maneuver. Image: NASA/Goddard/University of Arizona

As a result, plans to “weigh” the samples, a procedure requiring OSIRIS-REx to slowly spin about its axis, were called off and engineers moved up plans to stow TAGSAM and its robot arm to prevent the loss of additional material.

“We have abundant evidence of a successful collection event,” Lauretta told reporters during a 23 October teleconference. “We’re concerned that the sample mass measurement that was planned would import impart additional forces and actually cause us to lose mass.

“We’re in agreement that we have enough evidence of successful sample collection, that we don’t need the sample mass measurement. … That is not a prudent path to go down.”

The team also called off a planned thruster firing to halt OSIRIS-REx’s departure from Bennu in case an additional sample collection attempt was needed.

“I basically directed the team to put as minimal activity on the spacecraft as necessary, and start focusing on the early stow of sample to preserve and prevent any future mass loss,” Lauretta said.

Summing up, he said the sampling success was “very exciting, very surprising, but overall excellent news. We had a successful sample collection attempt, almost too successful. Material is escaping, and we’re expediting stow as a result of that.”

If all goes well, OSIRIS-REx will fire its main thruster and leave Bennu’s vicinity in March to begin a two-year voyage back to Earth. The samples, stowed in a re-entry capsule, are expected to land in Utah in September 2023.