Satellite-to-Satellite Tracking
The term satellite-to-satellite tracking summarizes methods of satellite geodesy in which the satellites carry out mutual distance measurements .
The previously common primary measurement from ground stations can be circumvented, as well as the resulting problems of orbit determination , refraction in the earth's atmosphere , etc.
introduction
When two artificial earth satellite behind the other at approximately the same path, the earth orbit, the distance remains between them is not constant but changes depending on the abnormalities of the gravity field . As an effect of somewhat uneven mass distribution on the earth's surface ( terrain ), in the earth's crust (geology) and in the earth's mantle (plate tectonics), neither gravity is constant in a constant orbit, nor is its direction centric to the center of the earth . Therefore, the orbital speed of the satellites is subject to small disturbance forces, which depend on the respective disturbance potential of the earth's body at the altitude.
As a result, there are constant deviations from a (trouble-free) Keplerbahn , which can add up to amounts in the kilometer range. They affect the mutual distance between two satellites flying one behind the other (depending on the distance) with sizes ranging from meters to hectometers .
Direct measurement of the web interference differences
The new technology of satellite-to-satellite tracking distance measurements is a very welcome addition to the previous methods of satellite geodesy and geoid determination . The measurement itself takes place z. B. electronically ( EDM ) or with microwaves - and can now be done with millimeter precision. A first, largely successful project is GRACE , in which two specially equipped geodetic satellites orbit the earth around the earth at a distance of around 200 kilometers.