Report of the Seasat Failure Review Board

The Seasat spacecraft failed on October 9, 1978, after satisfactory operation in orbit for 105 days, as a result of a loss of electrical power in the Agena bus that was used as a part of the spacecraft. This loss of power was caused by a massive and progressive short in one of the slip ring assemblies that was used to connect the rotating solar arrays into the power subsystem. The most likely cause of this short was the initiation of an arc between adjacent slip ring brush assemblies. The triggering mechanism of this arc could have been either a wire-to-brush assembly contact, a brush-to-brush contact, or a momentary short caused by a contaminant that bridged internal components of opposite electrical polarity. The slip ring assembly, as used in the Seasat spacecraft, was connected into the power subsystem in such a way that most of the adjacent brush assemblies were of opposite electrical polarity. This wiring arrangement, together with the congested nature of the design itself, made the Seasat slip ring assembly a unique, first-of-a-kind component that was particularly prone to shorting. The possibility of slip ring failures resulting from placing opposite electrical polarities on adjacent brush assemblies was known at least as early-as the summer of 1977 to other projects within the contractor's organization. Furthermore, failures of slip ring assemblies due to shorting between brushes had been experienced by the prime contractor on slip ring assemblies used by other programs. That the Seasat organization was not fully aware of these potential failure modes was due to a breakdown in communication within the contractor's organization.