Midcourse space experiment precision ephemeris

The Midcourse Space Experiment satellite, hosting a suite of state-of-the-art sensors, was launched into an 898-km altitude, nearly sun-synchronous orbit in April 1996, One of the primary tasks of the space surveillance principal investigator team was to evaluate the utility of the Midcourse Space Experiment sensors in performing space surveillance tasks. A critical issue in assessing the sensors' performance is the metric accuracy of their observations, which depends on the ephemeris accuracy of the satellite. In particular, to support the accuracy requirements of the Space-Based Visible, the primary space surveillance sensor onboard the satellite, the ephemeris accuracy goal was set at 15 m (1 sigma). There are two issues that had to be addressed in meeting this ephemeris accuracy goal: 1) the quantity and quality of the tracking data and 2) the dynamic modeling of the satellite's motion. The tracking of the satellite was performed by the U.S. Air Force Space Ground Link System of S-band radars, while Lincoln Laboratory's Millstone Hill radar in Westford, Massachusetts provided tracking data that were used to independently assess orbit accuracy. The most difficult aspect of the dynamic modeling of the satellite's motion was due to the effect of anomalous accelerations from cryogen gas venting, Results are presented that show the 15-m ephemeris accuracy goal has been met and exceeded.