NASA has confirmed that OSIRIS-REx has completed the last flyby over asteroid Bennu. The flyby was completed at about 6 AM EDT on April 7, leaving OSIRIS-REx slowly drifting away from the asteroid. Mission controllers have a few more days to wait before they’re able to find out how the spacecraft changed the surface of the asteroid after its sample collection mission.
The OSIRIS-REx team added the additional flyby of the asteroid to document surface changes that resulted from the Touch and Go sample collection maneuver conducted on October 20, 2020. Mission controllers said that surveying the distribution of the excavated material around the sample collection site allows them to learn more about the nature of the surface and subsurface materials along with mechanical properties of the asteroid.
During its final flyby, OSIRIS-REx imaged the asteroid for nearly 6 hours, covering more than a full rotation around Bennu. It flew within 2.1 miles of the surface, which is the closest the spacecraft has been since the sample collection event. It will be a few days before mission controllers have an idea of the landing site’s condition because it will take until at least April 13 for the spacecraft to downlink all of the data and new pictures.
OSIRIS-REx shares the Deep Space Network antennas used for relaying data with other NASA missions, including the Mars Perseverance Rover. OSIRIS-REx typically is allowed between four and six hours of downlink time per day. So far, mission controllers have received about 4000 megabytes of data collected during the flyby.
OSIRIS-REx is currently about 185 million miles from Earth, resulting in a slow downlink data rate of 412 kilobits per second. The limited-time the downlink is available per day, and the slow downlink rate means it will take several days for all of the data to be downloaded. OSIRIS-REx will remain in the vicinity of the asteroid until May 10, when its thrusters will fire, and the two-year journey home will begin.