The GEOSAT (GEOdetic SATellite) was a U.S. Navy Earth observation satellite launched into a 108° inclination orbit, with a nodal period of about 6040 seconds. The satellite carried a radar altimeter capable of measuring the distance from the satellite to the sea surface with a relative precision of about 5 cm. The initial phase was an 18-month classified Geodetic Mission (GM) have a ground track with a near-23-day repeat with closure to within 50 kilometers. The effect of atmospheric drag was such that by Fall 1986 GEOSAT was in an almost exact 23-day repeat orbit.