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A Block IIA GPS satellite
Mission type Navigation
Operator US Air Force
COSPAR ID 1993-032A[1]
SATCAT № 22657[1]
Mission duration 7.5 years (planned)[2]
Spacecraft properties
Spacecraft type GPS Block IIA[2]
Manufacturer Rockwell[2]
Launch mass 1,816 kilograms (4,004 lb)[2]
Start of mission
Launch date 13 May 1993, 00:07:00 (1993-05-13UTC00:07Z) UTC
Rocket Delta II 7925-9.5, D220[3]
Launch site Cape Canaveral LC-17A[3]
End of mission
Deactivated 20 December 2007 (2007-12-21)
Orbital parameters
Reference system Geocentric
Regime Medium Earth
Perigee 20,033 kilometres (12,448 mi)[4]
Apogee 20,327 kilometres (12,631 mi)[4]
Inclination 54.9 degrees[4]
Period 717.88 minutes[4]

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.[3] The launch took place from Launch Complex 17A at the Cape Canaveral Air Force Station,[5] and placed USA-91 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37XFP apogee motor.[2]

On 14 June 1993, USA-91 was in an orbit with a perigee of 20,033 kilometres (12,448 mi), an apogee of 20,327 kilometres (12,631 mi), a period of 717.88 minutes, and 54.9 degrees of inclination to the equator.[4] It broadcast signal PRN 07, and operated in slot 4 of plane C of the GPS constellation.[6] The satellite had a mass of 1,816 kilograms (4,004 lb). It had a design life of 7.5 years,[2] and ceased operations on 20 December 2007.


  1. ^ a b "Navstar 2A-11". US National Space Science Data Center. Retrieved 10 July 2012. 
  2. ^ a b c d e f Krebs, Gunter. "GPS-2A (Navstar-2A)". Gunter's Space Page. Retrieved 10 July 2012. 
  3. ^ a b c McDowell, Jonathan. "Launch Log". Jonathan's Space Page. Retrieved 10 July 2012. 
  4. ^ a b c d e McDowell, Jonathan. "Satellite Catalog". Jonathan's Space Page. Retrieved 10 July 2012. 
  5. ^ McDowell, Jonathan. "Launch List". Launch Vehicle Database. Jonathan's Space Page. Retrieved 10 July 2012. 
  6. ^ Wade, Mark. "Navstar". Encyclopedia Astronautica. Retrieved 10 July 2012.