Summary of the CTS Transient Event Counter Data after One Year of Operation

A spacecraft electrical system transient detector has been operating on the joint Canadian-American Communications Technology Satellite (CTS), now called Hermes, since January 31, 1976. This detector, called the transient event counter (TEC), senses and counts transients having a minimum amplitude of 5 volts and a rise time of less than 0.3 ¿sec. The transients in three separate wiring harnesses are counted: the attitude control harness, the solar array instrumentation harness and the solar array power harness. Recently, anomalous behavior of geosynchronous satellites has been attributed to the electrostatic charging of spacecraft surfaces by the environment during geomagnetic substorms. Insulating surface materials subjected to high electrical stress by such charging can discharge through electrical arcing. It is believed that the electromagnetic pulses from such discharges can couple into the spacecraft wiring harnesses and result in uncommanded switching of logic circuits, which in turn is responsible for the observed anomalies. The function of the TEC is to count such transients. This report describes the TEC and presents the flight data for a year of operation. A large number of transients have occurred but these have not caused any anomalous electronic switching events in the satellite systems. The character of the transients seems to imply that additional sensors are required to understand the discharge phenomenon on large satellites. The results of this experiment indicate that satellite system immunity to discharge-related electronic switching anomalies can be obtained by filtering out the harness transients.