The Touch-and-Go (TAG) Rehearsal mission phase involves rehearsing the events leading up to TAG, or the sample collection event. During the Checkpoint and Matchpoint rehearsals, the OSIRIS-REx mission team and spacecraft practice the various steps of the touchdown sequence.
The touchdown sequence includes two separate burns – the Checkpoint burn and the Matchpoint burn – that generate the spacecraft’s final trajectory down to the asteroid’s surface. At 410 ft (125 m) above Bennu, the spacecraft executes the Checkpoint burn, which adjusts the spacecraft’s position and speed down toward the altitude of the Matchpoint burn. The Matchpoint burn occurs at approximately 164 ft (50 m) from the asteroid’s surface and places the spacecraft on a trajectory that matches the rotation of Bennu as it further descends toward the targeted touchdown spot.
On Apr. 14, the mission pursued its first practice run – known as Checkpoint rehearsal. This rehearsal allowed the team to practice navigating the spacecraft through the Checkpoint burn to the location of the Matchpoint burn. The spacecraft’s activities included departing orbit, extending the robotic sampling arm out to the sample collection configuration, moving the solar arrays into a configuration that safely positions them away from the asteroid’s surface, collecting navigation images for the Natural Feature Tracking (NFT) guidance system, and capturing science data.
The team will perform these same activities during Matchpoint rehearsal on Aug. 11, and then navigate down to the Matchpoint burn altitude of approximately 82 ft (25 m) before backing away.
A primary goal of this mission phase is to perfect the steps of the sample collection event in preparation of the first sampling attempt. These rehearsals also allow the team to confirm that the spacecraft’s imaging, navigation and ranging systems operate as expected during the descent sequence. Additionally, they give the team a chance to ensure that the Natural Feature Tracking (NFT) guidance system accurately updates the spacecraft’s position and speed relative to Bennu as it descends towards the surface
Between rehearsals, the spacecraft will remain in a 0.7-mile (1.1-km) safe-home orbit around Bennu. It will also perform the Recon C low-altitude flyover of backup site Osprey on May 26.