Etalon

In contrast to GEO-IK, the Russian Etalon satellites reside in high altitude (19,100 km) orbits and are completely passive in nature. Each 1,415-kg satellite is a 1.294 m diameter sphere covered with 306 antenna arrays which in turn each contain 14 corner cubes for laser interrogation and reflecting. A small number of reflectors are made of germanium for "future infrared interferometric measurements" (Reference 483). To date only two Etalon satellites have been orbited, Kosmos 1989 (10 January 1989) and Kosmos 2024 (31 May 1989), and each accompanied a pair of GLONASS satellites on Proton launch vehicles.

The higher altitude of the Etalon satellites, when compared to similar laser-reflecting geodetic satellites of other nations, was selected to enhance several specific goals: "(1) the development of a high-accuracy global reference coordinate system and determination of the Earth's rotation parameters, (2) determination of lengths of long baselines, (3) improvement of the Earth's gravitational field parameters, and (4) improvement of the selenocentric gravitational constant" (Reference 483). The effect of non-gravitational forces on the orbits of the Etalon satellites was reported in late 1990 and further studies, including the effects of the Sun and the planets, were released in late 1993 (References 484-486).