Fleet Satellite Communications System (FLTSAT or FLTSATCOM)

The success of TACSAT led to the deployment in 1979 of the UHF/EHF Fleet Satellite Communications System (FLTSAT or FLTSATCOM) to support the US Navy and Air Force. Although principally for maritime use, the system was also used for aircraft as well as high-level command and control (the Strategic Air Command and the Presidential Command Network), strategic nuclear forces and other high priority users such as special forces. FLTSATCOM supported US military communications for over two decades.

FLTSATCOM was meant to be deployed in the early 1970s, but its delay led to the introduction of a MARISAT as a gap-filler satellite, GAPSAT.

FLTSATCOM-1 was launched on 9 February 1978 with 12×5-KHz channels (AFSAT), 10×25-kHz channels (FLTSAT) and 1×500-kHz channel (AFSAT) as well as one Navy Fleet Satellite Broadcast (FSB) channel with an SHF uplink and UHF downlink.

Eight satellites were launched between 1978 and 1989 with the system becoming operational in 1981—FLTSATCOM-2 on 4 May 1979, FLTSATCOM-3 on 18 January 1980; and FLTSATCOM-4 on 31 October 1980. FLTSATCOM-5 was launched on 6 August 1981, reached geostationary orbit but was limited by damage to the solar arrays. FLTSATCOM-7 was launched out of sequence on 5 December 1986. FLTSATCOM-6 failed on launch on 27 March 1987. FLTSATCOM-8 was launched on 25 September 1989.

The main body of the satellite was a hexagon structure,2.3 m wide and 1.27 m high, containing the payload and spacecraft modules. The bottom of the structure to the top of the offset spiral antenna mast measured 6.6 m. Two solar arrays, attached to booms extending from the spacecraft module, rotated to continually face the Sun, and produce a minimum of 1,259 W of power for at least five years. The solar wings measured 13.2 m tip-to-tip. Three 24-cell Ni-Cd batteries provided power during solar eclipse periods. Three-axis body stabilization was provided by redundant body-mounted momentum wheels which interacted with monopropellant hydrazine thrusters to maintain vehicle attitude, and keep antennas pointed at Earth. The satellite launch mass was 1,865 kg; in orbit it had a mass of 1,000 kg.

In the 1990s, the system was replaced by the UHF Follow-on (UFO) satellites. FLTSATCOM-7 and FLTSATCOM-8 continue to provide UHF communications.