Leveraging Resonant Terminator Orbits for the Trajectory Design of OSIRIS-APEX at (99942) Apophis

The OSIRIS-REx spacecraft has been approved for an extended mission (OSIRIS-APEX) to visit the asteroid (99942) Apophis. In this paper we outline a potential design for the spacecraft’s trajectory during the variable phase orbit segment of the APEX mission. This phase of the mission, nominally expected to begin in January2030, has the primary goal of collecting image and spectral data of the full asteroid surface at a wide variety of illumination conditions without requiring frequent firing of the spacecraft thrusters. This work will focus on leveraging resonant terminator orbits (RTOs) in order to satisfy these goals and the associated science requirements. Though this segment will occur after Apophis’ closest flyby of Earth in April 2029, the proposed design utilizes the current best estimates of the asteroid’s orbital elements and physical properties at that time when designing the spacecraft’s orbit.