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USA-50, also known as GPS II-6 and GPS SVN-18, was an American navigation satellite which formed part of the Global Positioning System. It was the sixth of nine Block II GPS satellites to be launched, which were the first operational GPS satellites to fly.

USA-50

Names	Navstar 2-06 GPS II-6 GPS SVN-18
Mission type	Navigation
Operator	U.S. Air Force
COSPAR ID	1990-008A
SATCAT no.	20452
Mission duration	7.5 years (planned) 10.5 years (achieved)
Spacecraft properties
Spacecraft	GPS II
Spacecraft type	GPS Block II[1]
Manufacturer	Rockwell International
Launch mass	840 kg (1,850 lb) [2]
Dimensions	5.3 m (17 ft) of long
Power	710 watts
Start of mission
Launch date	24 January 1990, 22:55:01 UTC
Rocket	Delta II 6925-9.5 (Delta D191) [3]
Launch site	Cape Canaveral, LC-17A
Contractor	McDonnell Douglas
Entered service	February 1990
End of mission
Deactivated	18 August 2000
Orbital parameters
Reference system	Geocentric orbit[4]
Regime	Medium Earth orbit (Semi-synchronous)
Slot	?
Perigee altitude	20,087 km (12,481 mi)
Apogee altitude	20,275 km (12,598 mi)
Inclination	54.6°
Period	717.92 minutes
Global Positioning System ← USA-49 (GPS II-5) USA-54 (GPS II-7) →

Background

It was part of the 21-satellite Global Positioning System (GPS) Block II series that provides precise position data (accurate to within 16 m) to military and civilian users worldwide. Its signals could be received on devices as small as a telephone. The GPS II satellites, built by Rockwell International for the Air Force Space Systems Division, each have a 7.5-year design life. The Air Force intends to launch a GPS II every 2 to 3 months until the constellation of 21 operational satellite and 3 spares is aloft. The GPS Block II join 7 operational Block 1 satellites.[2]

Launch

USA-50 was launched at 22:55:01 UTC on 24 January 1990, atop a Delta II launch vehicle, flight number D191, 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-50 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37XFP apogee motor.[1]

Mission

On 25 February 1990, USA-50 was in an orbit with a perigee of 20,087 km (12,481 mi), an apogee of 20,275 km (12,598 mi), a period of 717.92 minutes, and 54.6° 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] and was retired from service on 18 August 2000.

References

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