WASHINGTON — The leaders of NASA’s OSIRIS-REx mission are confident that the spacecraft collected material from the surface of the asteroid Bennu during a touch-and-go (TAG) maneuver Oct. 20.
At an Oct. 21 briefing nearly 24 hours after the spacecraft’s brief touchdown on the asteroid, project officials and NASA leadership said images taken by OSIRIS-REx during the TAG maneuver and returned to Earth hours later indicate the spacecraft touched down almost exactly where expected and encountered material that the spacecraft was designed to collect.
A sequence of images showed the sampling mechanism, known as TAGSAM, at the end of a robotic arm descending toward the surface. The TAGSAM hit the surface and released a bottle of nitrogen gas, kicking up material before the spacecraft ascended six seconds after touchdown.
Well, I definitely touched down on Bennu!
Preliminary data show the sampling head touched Bennu’s surface for approximately 6 seconds, within 3 feet (1 meter) of the targeted location. #ToBennuAndBack
— NASA’s OSIRIS-REx (@OSIRISREx) October 21, 2020
“It was every bit as beautiful as I thought it would be,” NASA Administrator Jim Bridenstine said of those images. “The OSIRIS-REx mission outperformed in every way.”
“The systems seem to have performed nominally. The surface of Bennu behaved very well. So, everything that we can see from these initial images indicates sampling success,” said Dante Lauretta, principal investigator for OSIRIS-REx at the University of Arizona.
The spacecraft descended right on target inside a small crater called Nightingale. “We’re over 320 million kilometers away from Earth at this point, and we touched this asteroid within a meter of where we intended to,” said Rich Burns, OSIRIS-REx project manager at NASA’s Goddard Space Flight Center. “That’s extraordinary and a real credit to our team.”
That on-target performance, though, would have been moot if the surface turned out to be too rocky. However, the material at the site appears to be relatively weak material. Lauretta noted that, in one image, the edge of the TAGSAM came down on a large rock about 20 centimeters across. In the next, taken 1.25 seconds later, the rock had broken apart. “Literally, we crushed it,” he said.
The TAGSAM appeared to push into the surface slightly, which Lauretta took as a good sign based on laboratory tests of the device. “Some of the best test results occurred when TAGSAM gets down underneath the surface just a little bit, and is able to fire to fire that nitrogen gas with regolith all around it,” he said.
However, it will still be several days before scientists know exactly how much material the spacecraft collected. First, a camera will take images of the TAGSAM, looking for evidence of material captured inside as well as that stuck to several pads on the bottom of the mechanism. Later, controllers will slowly spin the spacecraft to measure the change in its moment of inertia caused by the sample material, which Lauretta said should allow them to determine the mass of the material to an accuracy of about 20 grams.
The goal of the mission, formally known as Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, is to collect at least 60 grams of samples for return to Earth, although Lauretta and others involved with the mission hope they got much more. Officials will decide Oct. 30 if they met that goal and, if so, stow the sample and prepare to return to Earth, departing Bennu in March 2021 for an arrival at Earth in September 2023.
That will end the “science campaign” part of the OSIRIS-REx mission, Lauretta said. “There was a lot of interest from the science team on more data, more characterization of Bennu after the sampling attempt,” he said. “We gathered together as a management team and we evaluated that exact question very thoroughly. We agreed unanimously that this mission is about safe return of this sample. We do not want to do anything to put that sample at risk.”