NASA’s pioneering OSIRIS-REx probe has bagged up its precious asteroid sample for return to Earth.
OSIRIS-REx has finished stowing the bits of the carbon-rich asteroid Bennu that it snagged last Tuesday (Oct. 20), successfully locking the material into the spacecraft’s return capsule, mission team members announced Thursday (Oct. 29).
And the sample appears to be substantial—far heftier than the 2.1 ounces (60 grams) the mission had set as a target, team members said. Indeed, OSIRIS-REx collected so much material on Oct. 20 that its sampling head couldn’t close properly; the head’s sealing mylar flap was wedged open in places by protruding Bennu pebbles.
The OSIRIS-REx team noticed that issue last week when examining photos of the head and its collected sample; flakes of escaped asteroid material drifted through the frames. To minimize the amount lost, the team decided to expedite the precise and complex stowing procedure, which was supposed to happen next week.
So, over the course of 36 hours on Tuesday and Wednesday (Oct. 27 and Oct. 28), engineers directed OSIRIS-REx to deposit the sampling head, which sat at the end of the probe’s robotic arm, into the return capsule; tug on the head to make sure it was secured properly; sever connections with the robotic arm; and lock up the return capsule via the locking of two latches.
This was all done while OSIRIS-REx was about 205 million miles (330 million kilometers) from Earth, meaning it took 18.5 minutes for each command to reach OSIRIS-REx, and another 18.5 minutes for each update from the probe to come back down to Earth.
“We wanted to only attempt stow one time, and we wanted to make sure we were successful,” OSIRIS-REx mission operations manager Sandra Freund, of Lockheed Martin Space in Littleton, Colorado, said during a NASA news conference Thursday. “And we definitely were.”
The change of plans required a last-minute reallocation of time on NASA’s Deep Space Network (DSN), the system of radio telescopes that the agency uses to communicate with its far-flung probes. Because the stow operation was so important and so involved, OSIRIS-REx needed a large block of continuous DSN time, which other NASA missions sacrificed for the greater good.
It’s unclear exactly how much asteroid material now sits in OSIRIS-REx’s return capsule, which will come down to Earth in September 2023. The team canceled a planned post-sampling weighing procedure that would have involved spinning the probe, because this maneuver would have resulted in more sample loss. (Moving the arm—to photograph the sample and conduct the stow operation, for example—imparted grain-liberating acceleration, mission team members explained. So they wanted to minimize such motions.)
But there’s definitely a lot of asteroid material on board, said mission principal investigator Dante Lauretta of the University of Arizona.
The sampling operation on Oct. 20 went extremely well, Lauretta said, and the head penetrated deep into Bennu’s surface—perhaps 19 inches (48 centimeters) or more. The team is confident that OSIRIS-REx pretty much filled its sampling head that day, meaning it likely backed