USA-150, also known as GPS IIR-4 and GPS SVN-51, is an American navigation satellite which forms part of the Global Positioning System. It was the fourth Block IIR GPS satellite to be launched, out of thirteen in the original configuration, and twenty one overall. It was built by Lockheed Martin, using the AS-4000 satellite bus.^[2]

USA-150 was launched at 01:48:00 UTC on 11 May 2000, atop a Delta II carrier rocket, flight number D278, flying in the 7925-9.5 configuration.^[4] The launch took place from Space Launch Complex 17A at the Cape Canaveral Air Force Station,^[5] and placed USA-150 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37FM apogee motor.^[2]

By 11 June 2000, USA-150 was in an orbit with a perigee of 20,133 km (12,510 mi), an apogee of 20,234 km (12,573 mi), a period of 718.02 minutes, and 54.9° of inclination to the equator.^[6] It is used to broadcast the PRN 20 signal, and operates in slot 1 of plane E of the GPS constellation, having replaced USA-35, the first operational GPS satellite.^[7] The satellite has a mass of 2,032 kg (4,480 lb), and a design life of 10 years.^[2] As of 2012 it remains in service.