PRARE
PRARE ( P recise R is A nd R ange-rate E quipment ) is a system for radar-based distance measurement to satellite . It also includes a two-way measurement in which a transponder answers the incoming radio signals on a different frequency.
The accuracy of the system developed by German researchers around 1990 was below 6.5 cm from the start and has been further improved. The two-frequency measurement also allows a more precise recording of the refraction .
PRARE is only light in weight and could therefore be installed as a " black box " in various earth satellites . It serves u. a. for satellite-to-satellite tracking and for observing plate tectonics .