The location system GPSDR on Topex/Poseidon
The GPSDR (Global Positioning System Demonstration Receiver) is a tracking system that uses the GPS constellation of satellites to determine the exact position of a transmitter.
The GPSDR (28 kg without redundancy, 29 W), operating at 12,227.6 MHz and 1,575.4 MHz, receives signals from up to six GPS satellites. The GPS antenna is mounted on a long boom to reduce multipath effects which can severely corrupt the measurements.
These satellite data plus GPS tracking data from ground sites allow nearly geometric solutions. Precise tracking of the satellite is made possible by using the Kalman filtering technique and a new GPS differential ranging technique.
Function
The GPSDR supports precise orbit determination by the DORIS system. It also helps to improve gravity field models and provides data for satellite positioning accurate to about 50 metres and 50 nanoseconds.
Principle
The GPSDR receives dual-frequency navigation signals continuously and simultaneously from 16 GPS satellites. It uses these signals to acquire phase measurements accurate to about one millimetre and pseudo-range measurements accurate to about 10 centimetres.
Technical data
The onboard system consists of two independent receivers operating in cold redundancy, each with an omnidirectional antenna, low-noise amplifier, quartz oscillator, sampling converter and a baseband digital processor communicating via the bus interface.
Further information :
- International GPS Services
- Instrument Description: GPS (Nasa/JPL website)
Missions passées 
