During the Orbital A Phase, which began on Dec. 31, 2018, the OSIRIS-REx spacecraft is operating in a gravitationally-bound orbit around Bennu for the first time.
Unlike previous mission phases, there are no science requirements for Orbital A. Instead, this phase is designed to provide the mission team with experience navigating in close proximity to a small body. The spacecraft is circling Bennu at a distance between 0.99 and 1.3 miles (1.6 and 2.1 km) and is traveling around 0.11 mph (5 cm/sec), with each orbit lasting about 61.4 hours. This phase marks the closest that a spacecraft has ever orbited around a small body and makes Bennu the smallest object to ever have been orbited by a spacecraft.
An OpNav image showing Bennu’s southern hemisphere, taken Jan. 17, 2019 with NavCam 1.
During Orbital A, the navigation team will transition from star-based navigation to landmark-based navigation. Using landmarks – such as boulders and craters on Bennu’s surface – to determine the position of OSIRIS-REx allows the navigation team to maneuver the spacecraft very precisely, which will be critical during upcoming mission phases.
As OSIRIS-REx orbits Bennu, the spacecraft’s NavCam 1 navigation camera is regularly imaging the asteroid’s surface, even though its scientific camera suite (OCAMS) is not collecting data. The navigation team uses “OpNav” (short for optical navigation) images to monitor the spacecraft’s close orbit around the asteroid.
The Orbital A phase is scheduled to end on Feb. 28, 2019. Get an overview of all the phases of Asteroid Operations.