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From Wikipedia, the free encyclopedia

NamesNavstar 2A-11
Mission typeNavigation
OperatorU.S. Air Force
COSPAR ID1993-032A [1]
SATCAT no.22657
Mission duration7.5 years (planned)
14.5 years (achieved)
Spacecraft properties
SpacecraftGPS IIA
Spacecraft typeGPS Block IIA [2]
ManufacturerRockwell International
Launch mass840 kg (1,850 lb)
Dimensions5.3 m (17 ft) of long
Power710 watts
Start of mission
Launch date13 May 1993, 00:07:00 UTC
RocketDelta II 7925-9.5
(Delta D220)
Launch siteCape Canaveral, LC-17A
ContractorMcDonnell Douglas
Entered service14 June 1993
End of mission
DisposalGraveyard orbit
Deactivated18 March 2016
Last contact20 December 2007
Orbital parameters
Reference systemGeocentric orbit [3]
RegimeMedium Earth orbit
SlotC4 (slot 4 plane C)
Perigee altitude20,033 km (12,448 mi)
Apogee altitude20,334 km (12,635 mi)
Period717.88 minutes
← USA-90 (GPS IIA-10)
USA-92 (GPS IIA-12) →

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.


Global Positioning System (GPS) was developed by the U.S. Department of Defense to provide all-weather round-the-clock navigation capabilities for military ground, sea, and air forces. Since its implementation, GPS has also become an integral asset in numerous civilian applications and industries around the globe, including recreational used (e.g., boating, aircraft, hiking), corporate vehicle fleet tracking, and surveying. GPS employs 24 spacecraft in 20,200 km circular orbits inclined at 55.0°. These vehicles are placed in 6 orbit planes with four operational satellites in each plane.[1]

GPS Block 2 was the operational system, following the demonstration system composed of Block 1 (Navstar 1 - 11) spacecraft. These spacecraft were 3-axis stabilized, nadir pointing using reaction wheels. Dual solar arrays supplied 710 watts of power. They used S-band (SGLS) communications for control and telemetry and Ultra high frequency (UHF) cross-link between spacecraft. The payload consisted of two L-band navigation signals at 1575.42 MHz (L1) and 1227.60 MHz (L2). Each spacecraft carried 2 rubidium and 2 Cesium clocks and nuclear detonation detection sensors. Built by Rockwell Space Systems for the U.S. Air force, the spacecraft measured 5.3 m across with solar panels deployed and had a design life of 7.5 years.[1]


USA-91 was launched at 00:07:00 UTC on 13 May 1993, atop a Delta II launch vehicle, flight number D220, flying in the 7925-9.5 configuration.[4] The launch took place from Launch Complex 17A (LC-17A) at the Cape Canaveral Air Force Station (CCAFS),[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 km (12,448 mi), an apogee of 20,334 km (12,635 mi), a period of 717.88 minutes, and 54.9° of inclination to the equator.[3] It broadcast signal PRN 07, and operated in slot 4 of plane C of the GPS constellation.[6] The satellite had a mass of 840 kg (1,850 lb). It had a design life of 7.5 years,[2] 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 1000 km above the operational constellation on 18 March 2016.[7]


  1. ^ a b c "Display: Navstar 2A-11 1993-032A". NASA. 14 May 2020. Retrieved 19 December 2020. This article incorporates text from this source, which is in the public domain.
  2. ^ a b c Krebs, Gunter. "GPS-2A (Navstar-2A)". Gunter's Space Page. Retrieved 10 July 2012.
  3. ^ a b "Trajectory: Navstar 2A-11 1993-032A". NASA. 14 May 2020. Retrieved 19 December 2020. This article incorporates text from this source, which is in the public domain.
  4. ^ McDowell, Jonathan. "Launch Log". Jonathan's Space Report. Retrieved 10 July 2012.
  5. ^ McDowell, Jonathan. "Launch List". Launch Vehicle Database. Jonathan's Space Report. Retrieved 10 July 2012.
  6. ^ Wade, Mark. "Navstar". Encyclopedia Astronautica. Retrieved 10 July 2012.
  7. ^ "50 SW to dispose of two GPS satellites". United States Air Force. Retrieved 21 March 2016. This article incorporates text from this source, which is in the public domain.
This page was last edited on 20 December 2020, at 03:02
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