Opportunities for Greater Autonomy for Osiris-Apex Spacecraft Operations at Apophis

After the successful return of samples from asteroid Bennu in September 2023, the OSIRIS-REx spacecraft executed a divert maneuver to initiate a new mission: OSIRIS–Apophis Explorer (APEX). The APEX mission will re-purpose the OSIRIS-REx flight system to rendezvous with and survey the near-Earth asteroid Apophis just after that asteroid’s rare, close approach to Earth in April 2029. This paper will describe some of the unique challenges for the OSIRIS-REx mission operations team at Bennu and present some of the ground and flight updates that are being studied to increase autonomy and reduce the burden on the operations team at Apophis. Mission operations around Bennu were extremely challenging in large part due to its very small size of ~500 meters diameter, the smallest planetary body ever to be orbited by a spacecraft. Close orbits and flybys of Bennu required execution of propulsive maneuvers ranging in velocity from tens of centimeters per second to as little as 0.01 millimeters per second. This, in turn, required extremely precise modeling of small forces acting on the spacecraft and frequent ground-in-the-loop navigation updates, in which optical navigation images were downlinked, used to update a navigation solution in combination with radiometric tracking by the ground team, and subsequently used to update products that were sent up to the spacecraft, all within a 24-hour period. These 24-hour late-update cycles entailed two-shift operations that frequently required personnel to work evenings and weekends, pushing the envelope of what would be sustainable and affordable for a second asteroid encounter. Nevertheless, the APEX mission will characterize Apophis — which with an estimated mean diameter of 340 meters is even smaller than Bennu — at centimeter scales, similar to the dataset collected at Bennu. Given budgetary constraints for the APEX mission and lessons learned from Bennu operations, the team is studying several opportunities to implement more autonomous operations at Apophis. One example includes an expansion of the autonomous onboard navigation process that was utilized during the four-hour sample collection event at Bennu to enable autonomous targeting of most science observations at Apophis, dramatically reducing the number of 24-hour ground updates necessary. Several potential improvements to ground processes and tools are also being considered. The OSIRIS-APEX mission promises to expand scientific knowledge of the solar system by enabling close study of the tidal effects on Apophis from its close encounter with Earth, while demonstrating more autonomous deep space operations techniques that could apply to future missions.