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USA-54, also known as GPS II-7 and GPS SVN-20, was an American navigation satellite which formed part of the Global Positioning System. It was the seventh of nine Block II GPS satellites to be launched, which were the first operational GPS satellites to fly.

USA-54

Names	Navstar 2-07 GPS II-7 GPS SVN-20
Mission type	Navigation
Operator	U.S. Air Force
COSPAR ID	1990-025A
SATCAT no.	20533
Mission duration	7.5 years (planned) 6.5 years (achieved)
Spacecraft properties
Spacecraft	GPS II
Spacecraft type	GPS Block II[1]
Manufacturer	Rockwell International[1]
Launch mass	840 kg (1,850 lb) [2]
Dimensions	5.3 m (17 ft) of long
Power	710 watts
Start of mission
Launch date	26 March 1990, 02:45:01 UTC
Rocket	Delta II 6925-9.5 (Delta D193) [3]
Launch site	Cape Canaveral, LC-17A
Contractor	McDonnell Douglas
Entered service	April 1990
End of mission
Deactivated	21 May 1996
Orbital parameters
Reference system	Geocentric orbit[4]
Regime	Medium Earth orbit (Semi-synchronous)
Slot	?
Perigee altitude	20,089 km (12,483 mi)
Apogee altitude	20,268 km (12,594 mi)
Inclination	55.0°
Period	717.84 minutes
Global Positioning System ← USA-50 (GPS II-6) USA-63 (GPS II-8) →

Background

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.[2]

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.[2]

Launch

USA-54 was launched at 02:45:01 UTC on 26 March 1990, atop a Delta II launch vehicle, flight number D193, flying in the 6925-9.5 configuration.[3] The launch took place from Launch Complex 17A (LC-17A) at the Cape Canaveral Air Force Station (CCAFS),[5] and placed USA-54 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37XFP apogee motor.[1]

Mission

On 30 April 1990, USA-54 was in an orbit with a perigee of 20,089 km (12,483 mi), an apogee of 20,268 km (12,594 mi), a period of 717.84 minutes, and 55.0° of inclination to the equator.[4] The satellite had a mass of 840 kg (1,850 lb), and generated 710 watts of power.[2] It had a design life of 7.5 years,[1] however following problems with the satellite switching between timing standards, the satellite was declared unusable on 21 May 1996.[6]

References

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