A COTS-Based Attitude Dependent Contact Scheduling System

‡The mission architecture of the Gamma -ray Large Area Space Telescope (GLAST) requires a sophisticated ground system component for scheduling the downlink of science data . Contacts between the GLAST satellite and the Tracking and Data Relay Satellite System (TDRSS) are restricted by the limited field -of -view of the science data downlink antenna . In addition, contacts must be scheduled when permitted by the satellite’s complex and non -repeating attitude profile . Complicating the matter further, the long lead -time required to schedule TDRSS services, combined with the short duration of the downlink contact opportunities, mandates accurate GLAST orbit and attitude modeling . These circumstances require the development of a scheduling system that is capable of pre dictively and accurately modeling not only the orbital position of GLAST but also its attitude . This paper details the methods used in the design of a Commercial Off The Shelf (COTS) -based attitude -dependent TDRS S contact scheduling system that meets the u nique scheduling requirements of the GLAST mission, and it suggests a COTS -based scheduling approach to support future missions . The scheduling system applies filtering and smoothing algorithms to telemetered GPS data to produce high -accuracy predictive GL AST orbit ephemerides . Next, bus pointing commands from the GLAST Science Support Center are used to model the complexities of the two dynamic science gathering attitude modes . Attitude -dependent view periods are then generated between GLAST and each of th e supporting TDR Ss . Numerous scheduling constraints are then applied to account for various mission specific resource limitations . Next, an optimization engine is used to produce an optimized TDRS S contact schedule request which is sent to TDRSS scheduling for confirmation . Lastly, the confirmed TDRS S contact schedule is rectified with an updated ephemeris and adjusted bus pointing commands to produce a final science downlink contact schedule.