Etalon-1 and Etalon-2 are
geodetic satellites. They are designed to determine, with high accuracy, terrestrial reference frame and earth rotation parameters, to improve the gravity field, and to improve the gravitational constant. Each satellite is a high-density passive laser reflector in a very stable
medium Earth orbit
A medium Earth orbit (MEO) is an geocentric orbit, Earth-centered orbit with an altitude above a low Earth orbit (LEO) and below a high Earth orbit (HEO) – between above sea level. (MEO).
References
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Geodetic satellites
Laser ranging satellites
Russian space probes
Earth observation satellites of the Soviet Union
Spacecraft launched in 1989