USA-91

USA-91, also known as GPS IIA-11, GPS II-20 and GPS SVN-37, was an American navigation satellite which formed part of the Global Positioning System. It was the eleventh of nineteen Block IIA GPS satellites to be launched.

USA-91 was launched at 00:07:00 UTC on 13 May 1993, atop a Delta II carrier rocket, flight number D220, flying in the 7925-9.5 configuration. The launch took place from Launch Complex 17A at the Cape Canaveral Air Force Station, and placed USA-91 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37XFP apogee motor.

On 14 June 1993, USA-91 was in an orbit with a perigee of 20033 km, an apogee of 20327 km, a period of 717.88 minutes, and 54.9 degrees of inclination to the equator. It broadcast signal PRN 07, and operated in slot 4 of plane C of the GPS constellation. The satellite had a mass of 1816 kg. It had a design life of 7.5 years, and ceased operations on 20 December 2007.

Following decommissioning, it was kept as a reserve satellite. It was finally put in a disposal orbit approximately 1000km above the operational constellation on March 18, 2016.