SECOR

The method was developed around 1960 for satellite geodesy and first used at the end of 1962 launched flash satellite Anna 1B. It measures the distance between space ground station and satellite, answered by this measurement pulses with a transponder. The phase difference of the signals is a measure of the distance. The ambiguity is solved by use of four very different frequencies similar to the time tellurometer developed for terrestrial EDM.

A total of 14 small satellites were launched for the SECOR system, of which 10 successfully reached orbit. These satellites have also been designated by the name SECOR or alternatively with EGRS ( Electronic & Geodetic Ranging Satellite).

The measurement accuracy was 1-3 meters for the 1960s, a peak, but the construction of the ground stations is relatively complex ( Messhütte, medium roof antenna, control). Therefore, they were gradually closed down after successful completion of the SECOR Equatorial Network, which was the first survey network spanned the whole earth. A few years later you could with satellite lasers ( see Satellite Laser Ranging SLR) achieve even better accuracy, this is even in the millimeter range.