ENVIRONMENT-INDUCED ANOMALIES ON THE TDRS AND THE ROLE OF SPACECRAFT CHARGING

The Tracking and Data Relay Satellites TDRS-A (F-1), TDRS-C (F-3), and TDRS-D (F-4) have all experienced environment-induced anomalies. These anomalies were determined to be related to spacecraft charging based on their occurrence frequency, distribution in local time, and the environment at the time of the anomalies. One type of anomaly occurring in F-1 is believed to be the result of buried charging with shadowing from the spacecraft's antennas being the discharge trigger mechanism. The circuitry in the F-3 and F-4 spacecraft were modified to make them immune to this type of anomaly. However, F-3 and then F-4 both suffered a second type of anomaly also attributed to buried charging effects. In addition, F-1 and F-3 have experienced a third type of anomaly that appears to be associated with surface charging. These anomalies, the local plasma environment, and their relationship to spacecraft charging are discussed.