NAVSTAR 46 (also known as USA 145, and GPS 2R-3) is an American navigational spacecraft of the GPS fleet that was launched by a Delta 2 rocket from Cape Canaveral at 13:51 UT on 1999 October 07. This is the third of the 21 redesigned 2R series that may eventually replace the existing GPS fleet. With this launch, the GPS fleet now had 28 operational spacecraft. Initial orbital parameters are period 736.2 min, apogee 21,164 km, perigee 20,097 km, and inclination 53.1 deg.
The Global Positioning System (GPS) was developed by the US 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 degrees. These vehicles are placed in 6 orbit planes with four operational satellites in each plane. There are also four additional satellites orbiting as reserves.
GPS Block 2 was the operational system, following the demonstration system comprised of Block 1 (Navstar 1 - 11) spacecraft. These spacecraft are 3-axis stabilized, nadir pointing using reaction wheels. Dual solar arrays supplied 710 watts of power. They used S-band (SGLS) communications for control and telemetry and UHF cross-link between spacecraft. The payload consisted of two L-band navigation signals at 1575.42 MHz (L1) and 1227.60 MHz (L2). Each spacecraft carried 2 rubidium and 2 cesium clocks and nuclear detonation detection sensors. Built by Rockwell Space Systems for the US Air Force, the spacecraft measured 5.3 m across with solar panels deployed and had a design life of 7.5 years.
GPS navigational location had originally been at 100-meter accuracy for civilian use signals, and at 20-meter accuracy for military use signals. As of 2000 May 01, the DOD voided the intentional degradation of the accuracy for civilian use, and made it on a par with the military accuracy. But it retained the prerogative to degrade the accuracy at selected locations when necessary.
Alternate Names
Navstar 46
GPS 2R-3
USA 145
Facts in Brief
Launch Date: 1997-11-06
Launch Vehicle: Delta II 7925
Launch Site: Cape Canaveral, United States
Mass: 840.0 kg
Nominal Power: 710.0 W