Apr 20, 2020
This week, OSIRIS-REx continued TAG Rehearsal phase operations. On Apr. 14, the mission successfully executed the Checkpoint (CP) rehearsal – this was the first time the team and spacecraft rehearsed the initial steps of the sample collection sequence. During the rehearsal, the spacecraft departed its 1-km safe-home orbit, performed the Checkpoint maneuver and executed the back-away burn as expected. The Checkpoint maneuver is the first of two planned maneuvers during the final stage of the TAG sequence to establish and adjust the terminal descent trajectory targeting the Nightingale site. During this rehearsal the back-away burn executed as planned prior to the point in the trajectory where the second and final maneuver, the Matchpoint maneuver, will occur during TAG. It’s notable that this is the first time that the spacecraft has utilized its on-board Natural Feature Tracking system to update its trajectory estimate and adjust the CP maneuver to autonomously correct its course. That’s a huge first time event that executed flawlessly adding confidence to the performance of the flight system during this mission critical activity.
After performing the checkpoint burn at approximately 125 m above Bennu’s surface, the spacecraft descended to approximately 65 m, the lowest altitude it has ever reached, at which point it executed a back-away burn. As part of rehearsal activities, the spacecraft also deployed the TAGSAM arm from its folded, parked position out to the sample collection configuration. Some of the spacecraft’s instruments also collected science and navigation images and made spectrometry observations of the sample site, as will occur during the actual sample collection event.
Prior to the Checkpoint rehearsal on Apr. 11, the spacecraft performed a second phasing burn, TR1P2, to adjust its position and velocity for the rehearsal’s orbit departure maneuver. TR1P2 is now the smallest maneuver executed on the mission to-date at 0.115 mm/s.