Solar Dynamics Observatory (SDO) Ascent Planning and Momentum Management

The Solar Dynamics Observatory (SDO) has a mission to study the sun in unprecedented detail and its effects on Earth. SDO will reach its final mission orbit through a sequence of ascent maneuvers including an engineering burn, six major perigee raising burns, and three trim burns. Once it is in its mission orbit, there will be two station-keeping maneuvers a year to keep SDO at 102 degrees W longitude +/- 0.5 degrees. To achieve its goals it must maintain almost continuous ground contact. To maximize continuity of ground contact, momentum unloading maneuvers must be reduced to a minimum. Members of the Flight Dynamics and Attitude Control System teams collaborated to design systems and operational plans to properly manage the momentum during operations. The main objective of the SDO Momentum Management Planning (MMP) Utility is to provide a time and a target momentum for the next wheel momentum unload (usually referred to as ‘delta-H maneuver’). This is achieved by dynamical propagation of the total angular momentum coupled with a simplified version of the onboard wheel control algorithm to predict time evolution of each of four wheel speeds based on the anticipated history of the system momentum. A two-step procedure was designed to predict times when one of the wheel speeds would approach its upper limit if no delta-H maneuver is scheduled to prevent it. Based on this prediction, the MMP Utility provides the recommended time and a target momentum for the next delta-H maneuver. Reliability of MMP recommendations is restricted by the accuracy of a predicted external torque used for dynamical propagation. The Slew Planning and Momentum Management (SPAMM) environmental model provides