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. On 25 February 1990, USA-50 was in an orbit with a perigee of kilometre (mi), an apogee of kilometre (mi), a period of 717.92 minutes, and 54.6 degrees of inclination to the equator. The satellite had a mass of kilogram (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.