FLTSATCOM Battery Experience - Twelve Years On-orbit

he Fleet Satellite Communications System (FLTSATCOM) has been a key element of the worldwide military communications systems for more than a decade. This paper discusses the design and performance of the nickel-cadmium (NiCd) batteries used on the first four FLTSATCOM spacecraft. The first of these was launched in February 1978. Maximum depth of discharge has been 65 to 70% of rated capacity (55 to 60% of measured capacity). Battery management involves charging from a dedicated section of the solar array to a temperature-compensated voltage limit, followed by switch down to a low-rate trickle charge. Battery temperatures are maintained low, and periodic reconditioning to a low state of charge is performed to ensure long life and reliable operation. This paper summarizes an in-depth review of on-orbit operating data which revealed flawless battery performance. Capacities observed during solstice season reconditioning increase gradually during the initial, approximately 16 to 18, seasons, and decrease subsequently. This signature suggests that the batteries in the older spacecraft are entering the wear-out-mode portion of their life.