https://en.wikipedia.org/wiki/OSIRIS-REx#Sample_acquisition wrote:
<<Rehearsals were performed before the sampling event, during which the solar arrays were to be raised into a Y-shaped configuration to minimize the chance of dust accumulation during contact and provide more ground clearance in case the spacecraft tips over (up to 45°) during contact. The descent was very slow to minimize thruster firings prior to contact in order to reduce the likelihood of asteroid surface contamination by unreacted hydrazine propellant. Contact with the surface of Bennu was to be detected using accelerometers, and the impact force was meant to be dissipated by a spring in the TAGSAM arm.
Upon surface contact by the TAGSAM instrument, a burst of nitrogen gas was released, which was meant to blow regolith particles smaller than 2 cm into the sampler head at the end of the robotic arm. A five-second timer limited the collection time to mitigate the chance of a collision. After the timer expired, the back-away maneuver executed a safe departure from the asteroid.
The plan was then for OSIRIS-REx to perform a braking maneuver a few days later to halt the drift away from the asteroid in case it was necessary to return for another sampling attempt. It would then take images of the TAGSAM head to verify a sample had been acquired. If a sample was acquired, the spacecraft would rotate about the short axis of the sample arm to determine sample mass by measuring moment of inertia and determine if it was in excess of the required 60 g.
Both the braking and rotation maneuvers were canceled as images of the sample container clearly showed a large excess of material was collected, a portion of which was able to escape through the container's seal due to some material jamming the mechanism open. The collected material was scheduled for immediate storage in the Sample-Return Capsule. On 28 October 2020, the sample collector head was secured in the return capsule. Following the severance of the head from the collector arm, the arm will then be retracted into its launch configuration, and the Sample-Return Capsule lid will be closed and latched preparing to return to Earth.
In addition to the bulk sampling mechanism, contact pads on the end of the sampling head made of tiny stainless steel loops (Velcro) passively collected dust grains smaller than 1 mm.
On 20 October 2020 at 22:13 UTC, OSIRIS-REx successfully touched down on Bennu. NASA confirmed via images taken during sampling that the sampler had made contact. The spacecraft touched down within 92 cm of the target location. After imaging the TAGSAM head, NASA concluded that there are rocks wedged in the mylar flap that is meant to keep the sample in, causing the sample to slowly escape into space. In order to prevent further loss of the sample through the flaps, NASA canceled the previously-planned spinning maneuver to determine the mass of the sample as well as a navigational braking maneuver and decided to stow the sample on 27 October 2020 rather than 2 November 2020 as was originally planned, which was completed successfully. It was seen that the collector head hovering over the SRC after the TAGSAM arm moved it into the proper position for capture and later the collector head secured onto the capture ring in the Sample Return Capsule.
When the head was seated into the Sample-Return Capsule's capture ring on 28 October 2020, the spacecraft performed a "backout check", which commanded the TAGSAM arm to back out of the capsule. This maneuver is designed to tug on the collector head and ensure that the latches – which keep the collector head in place – are well secured. Following the test, the mission team received telemetry confirming that the head is properly secured in the Sample-Return Capsule. Thereafter, on 28 October 2020, two mechanical parts on the TAGSAM arm must first be disconnected – these are the tube that carried the nitrogen gas to the TAGSAM head during sample collection and the TAGSAM arm itself. Over the next several hours, the mission team commanded the spacecraft to cut the tube that stirred up the sample through the TAGSAM head during sample collection, and separate the collector head from the TAGSAM arm. Once the team confirmed these activities were done, it commanded the spacecraft on 28 October 2020, to close and seal the Sample-Return Capsule, the final step of the sample stowage process of Bennu's samples. To seal the SRC, the spacecraft closes the lid and then secures two internal latches. Additionally, on inspecting images, it was observed that a few particles had escaped from the collector head during the stowage procedure, but it was confirmed that no particles would hinder the stowage process, since the team was confident that a plentiful amount of material remains inside of the head, being more than the needed amount,60 g. Now, the sample of Bennu is safely stored and ready for its journey to Earth. Now that the collector head is secure inside the SRC, pieces of the sample will no longer be lost.>>
