Space Dynamics Laboratory
Utah State University
Logan, UT
www.usu.edu

In September 2020, NASA launched a spacecraft to a distant asteroid to help answer questions central to the human experience: Where did we come from and what is our destiny? With aid from the Space Dynamics Laboratory (SDL) at Utah State University, the agency is one step closer to answering those questions. Under the leadership of the University of Arizona’s Lunar and Planetary Laboratory, NASA’s Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft extended its articulated robotic arm on October 21 to collect debris, or regolith, from the surface of asteroid Bennu.

PolyCam (center), MapCam (left), and SamCam (right) make up the OSIRIS-REx Camera Suite responsible for most of the visible light images taken by the spacecraft. (University of Arizona/Symeon Platts)

SDL built the camera electronics for a three-camera suite onboard OSIRIS-REx named OCAMS. PolyCam enabled NASA to acquire images of Bennu from approximately 1.2 million miles away and assisted with the spacecraft’s navigation to the asteroid during approach. MapCam was responsible for searching the asteroid for a suitable place to collect the sample. It also mapped Bennu and searched for outgassing plumes and other debris ejected from the asteroid. SamCam is a close-range camera that verified the sample acquisition and will image the sampling mechanism.

The spacecraft captured images of the sample collector head as it moved through several different positions. In reviewing these images, the OSIRIS-REx team noticed both that the head appeared to be full of asteroid particles and that some of these particles appeared to be escaping slowly from the sample collector, called the Touch-And-Go Sample Acquisition Mechanism (TAGSAM) head — the arm on the spacecraft responsible for collecting Bennu’s regolith sample. During the touch-and-go maneuver, the sampler head was extended toward Bennu. The momentum of the spacecraft’s slow, downward trajectory pushed the sampler head against the asteroid’s surface for about ten seconds — just long enough to obtain a sample.

(Top) The OSIRIS-REx collector head hovering over the Sample Return Capsule (SRC) after the Touch-And-Go Sample Acquisition Mechanism arm moved it into the proper position for capture. (Bottom) The collector head secured onto the capture ring in the SRC. Both images were captured by the StowCam camera. (NASA/Goddard/University of Arizona/Lockheed Martin)

At contact, the spacecraft fired nitrogen gas onto the surface to roil up dust and small pebbles, which were then captured. Preliminary data showed the one-foot-wide (0.3-meter-wide) sampling head touched Bennu’s surface for approximately six seconds, after which the spacecraft performed a back-away burn, firing its thruster to back away from the asteroid’s surface.

The mission team measured the sample amount by spinning the spacecraft with the collection arm extended. The team compared the change in the spacecraft’s inertia with a previous, empty TAGSAM spin to ensure that enough sample was collected. The TAGSAM head was then placed in the Sample Return Capsule for return to Earth. After successful stowage, the spacecraft slowly drifted away from Bennu to a safe distance, where it will stay until its departure this year for the Return Cruise Phase back to Earth.

The mission team spent two days working around the clock to carry out the stowage procedure. The process to stow the sample is unique compared to other spacecraft operations and required the team’s continuous oversight and input over the two-day period. For the spacecraft to proceed with each step in the stowage sequence, the team had to assess images and telemetry from the previous step to confirm the operation was successful and the spacecraft was ready to continue.

Additionally, the team inspected images to observe any material escaping from the collector head to confirm that no particles would hinder the stowage process. StowCam images of the stowage sequence show that a few particles escaped during the stowage procedure but the team is confident that a plentiful amount of material remains inside the head.

The stowage process was expedited after sample collection when the mission team received images that showed the spacecraft’s collector head overflowing with material. The images indicated that the spacecraft collected well over 2 ounces (60 grams) of Bennu’s surface material.

The OSIRIS-REx team will now focus on preparing the spacecraft for the next phase of the mission — Earth Return Cruise. The departure window opens in March for OSIRIS-REx to begin its voyage home and the spacecraft is targeting a landing in the Utah desert in September 2023.

“It is incredibly exciting to be involved with missions like OSIRIS-REx,” said Alan Thurgood, SDL’s Civil and Commercial Space division director. “Being a part of exciting science with historically significant missions and pushing human knowledge forward motivates our team at SDL to do great work.”

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This article first appeared in the January, 2021 issue of Tech Briefs Magazine.

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