OPS 5118

OPS 5118, also known as Navstar 6, GPS I-6 and GPS SVN-6, was an American navigation satellite launched in 1980 as part of the Global Positioning System development programme. It was the sixth of eleven Block I GPS satellites to be launched.

Background
Global Positioning System (GPS) was developed by the U.S. Department of Defense to provide all-weather round-the-clock navigation capabilities for military ground, sea, and air forces. Since its implementation, GPS has also become an integral asset in numerous civilian applications and industries around the globe, including recreational used (e.g., boating, aircraft, hiking), corporate vehicle fleet tracking, and surveying. GPS employs 24 spacecraft in 20,200 km circular orbits inclined at 55°. These vehicles are placed in 6 orbit planes with four operational satellites in each plane.

Spacecraft
The first eleven spacecraft (GPS Block 1) were used to demonstrate the feasibility of the GPS system. They were 3-axis stabilized, nadir pointing using reaction wheels. Dual solar arrays supplied over 400 watts. They had S-band communications for control and telemetry and Ultra high frequency (UHF) cross-link between spacecraft. They were manufactured by Rockwell Space Systems, were 5.3 meters across with solar panels deployed, and had a design life expectancy of 5 years. Unlike the later operational satellites, GPS Block 1 spacecraft were inclined at 63°.

Launch
OPS 5118 was launched at 22:00 UTC on 26 April 1980, atop an Atlas F launch vehicle with an SGS-1 upper stage. The Atlas used had the serial number 34F, and was originally built as an Atlas F. The launch took place from Space Launch Complex 3E at Vandenberg Air Force Base, and placed OPS 5118 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-27 apogee motor.

Mission
By 16 May 1980, OPS 5118 had been raised to an orbit with a perigee of 20006 km, an apogee of 20357 km, a period of 717.94 minutes, and 62.8° of inclination to the equator. The satellite had a design life of 5 years and a mass of 758 kg. It broadcast the PRN 09 signal in the GPS demonstration constellation, and was retired from service on 6 March 1991.