OSIRIS-REX NAVIGATION PERFORMANCE DURING FIRST LEG OF OUTBOUND CRUISE

The NASA New Frontiers-class OSIRIS-REx mission is currently midway on its two-year interplanetary trajectory to rendezvous with the rare B-type near-earth asteroid Bennu (101955) in the fall of 2018. The spacecraft was directed during the first half of its journey to return to Earth for an Earth Gravity Assist (EGA) on September 22, 2017. This paper will summarize the performance of the spacecraft navigation over the first year of operations, which is exceeding expectations from prelaunch analysis. The navigation performance has benefitted from excellent performance of the main engine, trajectory correction maneuvers and attitude control system maneuvers, the well-balanced momentum desaturation maneuvers, and the quantity and quality of Deep Space Network 2-way X-band Doppler, range and delta-Differential One-way Range (ODOR) measurements. The combination of the ODOR with the traditional radio-metric data has allowed the navigation team to finely characterize the small forces influencing the spacecraft motion such as the outgassing, solar pressure and the force due to spacecraft thermal re-radiation. These forces need to be determined to a high level of accuracy to meet position requirements during proximity operations in the vicinity of Bennu. Comparisons of the current AV cost, maneuver magnitudes, expected orbit determination accuracies to the pre-launch analysis are presented.