|Operator||US Air Force|
|Mission duration||5 years (planned)|
7 1⁄2 years (achieved)
|Spacecraft type||GPS Block I|
|Launch mass||759 kilograms (1,673 lb)|
|Start of mission|
|Launch date||22 February 1978, 23:44UTC|
|Rocket||Atlas E/F SGS-1, 64F|
|Launch site||Vandenberg SLC-3E|
|End of mission|
|Deactivated||17 July 1985|
|Perigee altitude||20,075 kilometres (12,474 mi)|
|Apogee altitude||20,291 kilometres (12,608 mi)|
OPS 5111, also known as Navstar 1, NDS-1, GPS I-1 and GPS SVN-1, was an American navigation satellite launched in 1978 as part of the Global Positioning System development programme. It was the first GPS satellite to be launched, and one of eleven Block I demonstration satellites.
OPS 5111 was launched at 23:44 UTC on 22 February 1978, atop an Atlas E/F carrier rocket with an SGS-1 upper stage. The Atlas used had the serial number 64F, 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 5111 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-27 apogee motor.
By 11 April 1978, OPS 5111 was in an orbit with a perigee of 20,075 kilometres (12,474 mi), an apogee of 20,291 kilometres (12,608 mi), a period of 718 minutes, and 63.3 degrees of inclination to the equator. The satellite had a design life of 5 years and a mass of 758 kilograms (1,671 lb). It broadcast the PRN 04 signal in the GPS demonstration constellation, and was retired from service on 17 July 1985.
- "Navstar 1". US National Space Science Data Center. Retrieved 12 July 2012.
- Krebs, Gunter. "GPS (Navstar)". Gunter's Space Page. Retrieved 12 July 2012.
- McDowell, Jonathan. "Launch Log". Jonathan's Space Page. Retrieved 12 July 2012.
- McDowell, Jonathan. "Satellite Catalog". Jonathan's Space Page. Retrieved 12 July 2012.
- McDowell, Jonathan. "Launch List". Launch Vehicle Database. Jonathan's Space Page. Retrieved 12 July 2012.
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