PRARE
The Precise RAnge and Range-Rate Equipment (PRARE) was developed and maintained as a national German experiment by the Institute for Navigation (INS) of the University of Stuttgart, the GeoForschungsZentrum Potsdam, Time Tech GmbH Stuttgart, and Kayser-Threde GmbH Munich. Development is funded by BMFT (Germany's Federal Ministry for Research and Technology). PRARE was flown on the European Space Agency (ESA) European Remote Sensing Satellites ERS-1 and ERS-2 and will be flown on the ESA ENVISAT. PRARE is a highly accurate microwave ranging system, supported by a network of mobile ground stations, which are used for orbit determination at decimeter level of accuracy as well as for various geodetic applications. The PRARE is designed to: - provide, in all weather conditions, precise satellite-to-ground or ground-to-satellite range and range-rate information - guarantee very reliable measurements through cross-checks and calibration procedures - ensure highly effective operation of the ground segment through data collection and dissemination via the satellite itself and control of the global network via one central ground station - allow fast product generation at an archiving, processing and distribution centre. In this two-way microwave ranging system, the on-board equipment performs the measurements in X-band (8.5 GHz), with some additional functions in S-band (2.2 GHz) for ionospheric correction purposes. The PRARE measures range and Doppler (range rate) between the satellite's antenna and up to four ground stations simultaneously. It is an autonomous system for precise satellite orbit observation. It consists of the space segment with its own computer and data storage medium, and the ground segment, the unattended user ground stations, a dedicated command station and a master station for receiving the data dumps. PRARE operates in X-band and, in the downlink, also in S-band. Thus, the ionospheric total electron content (TEC) can be determined along the line-of-sight from the ground station to the satellite. The applications of PRARE are: - precise satellite orbit determination (e.g. of altimeter and geodynamic satellites) - earth gravity field recovery - precise point positioning (tectonics) - earth rotation parameter determination and measurement of the ionospheric total electron content (TEC). In the measurement process the space segment is the active part, i.e. the satellite is the start and end point of the two-way line and the Range and Doppler correlations take place on-board. A ground station only turns the signal around after amplification and after modulating the S/X-band travel time difference and meteorological data on the carrier. All data are collected on-board and dumped during contact with the master station. The space segment also provides updated orbit and schedule data to the ground stations in the downlink. With this design it is possible to operate a global ground station network without external data transmission facilities. Especially important is that even the host satellite is not encumbered by the PRARE data flow. Related URL: "http://op.gfz-potsdam.de/prare/general/general.html" "http://earth.esa.int/ers/prare" Reference online documentation: "http://earth.esa.int/services/esa_doc/doc_pra.html" For any query, please refer to: ESA/ESRIN Earth Observation Help Desk "http://earth.esa.int" E-mail: eohelp@esa.int Phone: +39 06 94180777 Fax: +39 06 94180292 Address: ESA/ESRIN Via G.Galilei 00044 Frascati Italy
Positioning/Navigation