PRARE one resp. two years in orbit-performance analysis of the instruments´ oscillators onboard ERS-2 and Meteor-3/7

The precise range and range-rate equipment (PRARE) is a new space-borne microwave satellite tracking system, which has been operational since end of April 1995 in redundant configuration onboard the European remote sensing satellite ERS-2. For system function verification, an identical flight model had been tested between February 1994 and September 1995 onboard the Russian meteorological satellite Meteor-3/7. The system´s primary function is to measure very precisely range and range-rate between the space segment and dedicated PRARE ground-station transponders which are distributed around the Earth. From these basic measurements, which have a precision below 3 cm and 0.1 mm/s respectively, several higher level products are derived, such as precise orbits, Earth rotation and gravity field parameters, and clock synchronization quantities. The measurement signals are basically derived from one central oscillator inside the space segment. Analyses of the long-time behaviour of the two instruments´ oscillators, which are generated on a routine basis at the PRARE Master Station Oberpfaffenhofen, the accurate modelling of their UTC-related time scales, and results of occasional remote clock synchronization experiments are presented. The excellent suitability of the system for alternative usage as for example highly precise time transfer between remote atomic standards becomes obvious