USA-50

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.

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.

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. The launch took place from Launch Complex 17A (LC-17A) at the Cape Canaveral Air Force Station (CCAFS), and placed USA-50 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37XFP apogee motor.

Mission
On 25 February 1990, USA-50 was in an orbit with a perigee of 20087 km, an apogee of 20275 km, a period of 717.92 minutes, and 54.6° of inclination to the equator. The satellite had a mass of 840 kg, and generated 710 watts of power. It had a design life of 7.5 years, and was retired from service on 18 August 2000.