Alternative Sample Mass Measurement Technique for OSIRIS-REX Sample Collection Phase

The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft is the third NASA New Frontiers Program mission and arrived at the near-Earth asteroid (101955) Bennu in December 2018. Following completion of sample collection in October 2020, otherwise known as Touch-And-Go (TAG), the OSIRIS-REx spacecraft was set to verify its collected sample mass requirement (> 60g of material). The thoroughly tested Sample Mass Measurement (SMM) method was to be used for this verification. Imaging of the Touch-And-Go Sample Acquisition Mechanism (TAGSAM) was received shortly following the TAG event, intended to ensure mechanism health prior to moving forward with the SMM activity. These images displayed sample leakage, prompting discussion for alternative paths forward. Risk of continued sample loss and a desire to retain as much material as possible lead the team to pursue an accelerated sample stow schedule and forgo the planned SMM activity. Once the sample was safely stowed in the return capsule an alternative SMM method was proposed. The alternative SMM technique utilized reaction wheel momentum data from identical TAGSAM movements prior to and following the TAG event to estimate changes in spacecraft moment of inertia. Conservation of momentum was used to isolate the sample mass from this inertia change. Using this new method, the spacecraft team was able to successfully estimate collected sample mass to be 250.37 ± 101 g.