|Operator||US Air Force|
|Mission duration||7.5 years (planned)|
|Spacecraft type||GPS Block II|
|Launch mass||840 kilograms (1,850 lb)|
|Start of mission|
|Launch date||24 January 1990, 22:55:01UTC|
|Rocket||Delta II 6925, D191|
|Launch site||Cape Canaveral LC-17A|
|End of mission|
|Deactivated||18 August 2000|
|Perigee altitude||20,087 kilometres (12,481 mi)|
|Apogee altitude||20,275 kilometres (12,598 mi)|
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 was launched at 22:55:01 UTC on 24 January 1990, atop a Delta II carrier rocket, flight number D191, flying in the 6925 configuration. The launch took place from Launch Complex 17A at the Cape Canaveral Air Force Station, and placed USA-50 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37XFP apogee motor.
On 25 February 1990, USA-50 was in an orbit with a perigee of 20,087 kilometres (12,481 mi), an apogee of 20,275 kilometres (12,598 mi), a period of 717.92 minutes, and 54.6 degrees of inclination to the equator. The satellite had a mass of 840 kilograms (1,850 lb), and generated 710 watts of power. It had a design life of 7.5 years, and was retired from service on 18 August 2000.