ESA GNC Conference Papers Repository
Orbit determination strategy and simulation performance for OSIRIS-REx proximity operations
The Origins Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-REx) is a NASA New Frontiers mission to the near-earth asteroid Bennu (101955) that will rendezvous in 2018, create a comprehensive and detailed set of observations over several years, collect a regolith sample, and return the sample to Earth in 2023. The Orbit Determination (OD) team is a sub-section of the Flight Dynamics System (FDS) responsible for generating precise reconstructions and predictions of the spacecraft trajectory. The OD team processes radiometric data, LIDAR, as well as center-finding and landmark-based Optical Navigation (OpNav) images throughout the proximity operations phase to estimate and predict the spacecraft location within several meters. Stringent knowledge requirements stress the OD team's concept of operations and procedures to produce verified and consistent high quality solutions for observation planning, maneuver planning, and onboard sequencing. The first several phases of Bennu Proximity Operations will stress the OD team's ability to respond quickly to a dramatically different dynamical environment than that experienced during cruise. The Approach phase begins with the first attempts to acquire optical images of Bennu as a point source. As the approach progresses, Bennu will become a resolved extended object in the field-of-view. During this phase, initial observation opportunities necessary to generate an asteroid shape model are conducted. This phase is susceptible to introducing systematic biases that may be present through the first few Proximity Operations phases, thus care must be taken to produce and ensure that the OD reconstructions and predictions are of the best quality. Preliminary Survey continues the use of center finding OpNav images with radiometric data through a series of hyperbolic flybys to begin estimating Bennu's gravity. Once the gravity is estimated to a few percent, the transition to Orbital-A occurs with orbital insertion through several maneuvers to circularize into a 1.5 km orbit. Orbital-A's major objective is to allow for the Navigation Team to transition from the star-based center-finding OpNav images to landmark-based navigation. During this phase, it is the OD team's responsibility to produce late maneuver updates and periodic on-board ephemeris updates to maintain Bennu in the OpNav image field-of-view. The transition to landmark navigation is vital to obtain more precise OD required to meet challenging ephemeris prediction accuracy requirements for the highest resolution science observations in subsequent mission phases. This paper will provide insight into the OD concept of operations and summarize the OD performance expected during the approach and early proximity operation phases, based on our pre-encounter knowledge of Bennu. Strategies and methods used to compare and evaluate predicted and reconstructed solutions are detailed. The use of high fidelity operational tests during early 2017 will stress the teams concept of operations and ability to produce precise OD solutions with minimal turn-around delay. The Approach phase operational test will stress the OD team's ability to ingest star-based center-finding OpNav images and produce reconstructed and predicted trajectories several times a week for approach maneuver reconstruction and design respectively. The next operational test covers the critical orbital insertion phase of the mission in which OD solutions must be generated daily, with design updates for critical maneuver design events performed in the final 24 hours before the burn. Orbital-A provides a time for the navigation team to focus on the transition from center-finding OpNav images to landmark-based OpNav. This operational test covers several days of simulated OpNav images with systematic biases and random noise to produce the most realistic simulation of landmark based navigation yet. This operational test will stress the team's ability to respond to these error sources and validate the concept of operations necessary to successful complete the remaining proximity operation phases.