Geodetic Satellites

artificial earth satellites launched as objects of observation for the solution of problems of satellite geodesy. The direction to a particular satellite (positional observations) and the distance to it, which are calculated from observations, serve as the data for the solution of such problems. Geodetic links between points on the earth, separated from each other by up to several thousand kilometers (for example, in intercontinental cosmic triangulation), are established by means of positional photographic observations of the satellite moving at an altitude of 4,000-6,000 km simultaneously from two or more points. In order to ensure such observations using satellite photographic cameras of medium dimensions, inflatable geodetic satellite balloons of aluminized plastic film are launched, having diameters of 30-40 m. Much larger satellites are used in dynamic satellite geodesy. Their motion depends to a lesser degree on the heterogeneity of the atmosphere but is basically determined by the nature of the earth’s gravitational field. Such geodetic satellites are launched to altitudes of up to 3,000 km.

Special equipment is installed on geodetic satellites in order to increase the accuracy of simultaneous positional observations and of measurements of the distances to the satellites. Powerful impulse sources of light, which are controlled by on-board quartz watches and are operated from the earth, facilitate positional observations and allow, with the simultaneous participation of several stations, their synchronization with a great degree of precision.

Transponders, which relay radio signals sent to the geodetic satellite by stations on earth, allow us to determine the distance to the satellite by measuring the phase shift of the signal received at the station relative to the signal transmitted. Distances to geodetic satellites are also determined by analyzing the changes in the frequency of the signals of the radio transmitters installed on the geodetic satellites as a result of the Doppler effect. Corner reflectors are set up on the geodetic satellites for measuring distances using satellite laser range finders. The first geodetic satellite was the American satellite ANNA IB, launched in 1962, which was equipped with flash lamps.