Etalon is a series Soviet passive geodetic satellites; Etalon means "standard." Each is spherical and covered with 306 antenna arrays, each array containing 14 corer cubes for laser reflection. Etalons were designed and launched to enable the complete characterization of Earth's gravitational field at the altitude and inclination planned for the Glonass navigation satellites. They were also used to refine understanding of the Earth-Moon gravitational system, to determine the effect of non-gravitational forces on satellites, and for geophysical research. Only two Etalon satellites have been orbited, each accompanied by a pair of GLONASS satellites. Each was launched by a Proton rocket from Baikonur, measured 1.3 × 1.3 m, and had a mass of 1,415 kilograms.