MARISAT

MARISAT was a U.S. maritime satellite communications system that provided an interim operational capability for mobile users—primarily maritime—prior to the deployment of FLTSATCOM. Three MARISAT gapfiller (GAP) satellites were launched in 1976: MARISAT F-1 on 19 February, MARISAT F-2 on 10 June, and MARISAT F-3 on 14 October. The satellites were positioned to provide coverage of the Atlantic, Pacific, and Indian Ocean regions at nominal longitudes of approximately 345°E (15°W), 176.5°E, and 72.5°E, respectively. From 1981 onward, MARISAT services were progressively superseded by Inmarsat.

Each MARISAT satellite carried payloads operating in L band for maritime mobile services and C-band for feeder links, together with UHF transponders supporting military and government users. The UHF payload comprised two 25-kHz channels and one 500-kHz channel. Electrical power available to the communications payload was approximately 330 W.

Although designed for a nominal five-year service life, all three MARISAT satellites operated far longer. MARISAT F-1 was initially operated at 345°E from 1976 to 1990, then relocated to 254°E (106°W) to provide coverage of the Americas until its transfer to a disposal orbit in 1997. MARISAT F-2 operated near 176°E from 1976 to 1991, was subsequently relocated to several longitudes, and remained in service until October 2008 before final disposal. MARISAT F-3 operated at 72.5°E until the late 1990s, when it was moved to a disposal orbit, having accumulated approximately 32 years of service—one of the longest operational lifetimes achieved by a commercial communications satellite.