A spacecraft about the size of an SUV continues operations at an asteroid the size of a mountain. The spacecraft is OSIRIS-REx, the asteroid Bennu, and yesterday’s successful touchdown and sample collection attempt elicits nothing but admiration for the science team that offered up the SUV comparison. They’re collecting materials with a robotic device 321 million kilometers from home. Yesterday’s operations seem to have gone off without a hitch, the only lingering question being whether the sample is sufficient, or whether further sampling in January will be needed.

If all goes well, we will acquire the largest surface sample from another world since Apollo. TAGSAM is the Touch-And-Go Sample Acquisition Mechanism aboard the craft, a 3.35-meter sampling arm extended from the spacecraft as OSIRIS-REx was descending roughly 800 meters to the surface. The ‘Checkpoint’ burn occurred at 125 meters as the craft maneuvered to reach the sample collection site, dubbed ‘Nightingale.’ The ‘Matchpoint’ burn followed ‘Checkpoint’ by 10 minutes to match Bennu’s rotation at point of contact. A coast past the ‘Mount Doom’ boulder was followed by touchdown in a crater relatively free of rocks.

This is dramatic stuff. The image below is actually from August during a rehearsal for the sample collection (images of yesterday’s touchdown are to be downlinked to Earth later today), but it’s an animated view that gets across the excitement of the event. Mission principal investigator Dante Lauretta (University of Arizona. Tucson) had plenty of good things to say about the result:

“After over a decade of planning, the team is overjoyed at the success of today’s sampling attempt. Even though we have some work ahead of us to determine the outcome of the event – the successful contact, the TAGSAM gas firing, and back-away from Bennu are major accomplishments for the team. I look forward to analyzing the data to determine the mass of sample collected.”

Image: Captured on Aug. 11, 2020 during the second rehearsal of the OSIRIS-REx mission’s sample collection event, this series of images shows the SamCam imager’s field of view as the NASA spacecraft approaches asteroid Bennu’s surface. The rehearsal brought the spacecraft through the first three maneuvers of the sampling sequence to a point approximately 40 meters above the surface, after which the spacecraft performed a back-away burn. Credit: NASA/Goddard/University of Arizona.

The goal is 60 grams of material, with the first indication of sample size being new images of the surface to see how much material was disturbed by the TAGSAM activities. Michael Moreau (NASA GSFC) is OSIRIS-REx deputy project manager:

“Our first indication of whether we were successful in collecting a sample will come on October 21 when we downlink the back-away movie from the spacecraft. If TAG made a significant disturbance of the surface, we likely collected a lot of material.”

Images of the TAGSAM head, taken with the camera known as SamCam, should provide evidence of dust and rock in the collector, with some possibility of seeing inside the head to look for evidence of the sample within. Beyond imagery, controllers will try to determine the spacecraft’s moment of inertia by extending the TAGSAM arm and spinning the spacecraft about an axis perpendicular to the arm. Comparison to data from a similar maneuver before the sampling should allow engineers to measure the change in the mass of the collection head.

Between the imagery and the mass measurement, we should learn whether at least 60 grams of surface material have been collected. Once this has been verified, the sample collector head can be placed into the Sample Return Capsule (SRC) and the sample arm retracted as controllers look to a departure from Bennu in March of 2021. If necessary, a second maneuver, at the landing backup site called ‘Osprey,’ could take place on January 12, 2021.

Image: These images show the OSIRIS-REx Touch-and-Go Sample Acquisition Mechanism (TAGSAM) sampling head extended from the spacecraft at the end of the TAGSAM arm. The spacecraft’s SamCam camera captured the images on Nov. 14, 2018 as part of a visual checkout of the TAGSAM system, which was developed by Lockheed Martin Space to acquire a sample of asteroid material in a low-gravity environment. The imaging was a rehearsal for a series of observations that will be taken at Bennu directly after sample collection. Credit: NASA/Goddard/University of Arizona.

Sample return is scheduled for September 24, 2023, with the Sample Return Capsule descending by parachute into the western desert of Utah. So far so good, and congratulations all around to the OSIRIS-REx team!