The U.S. Navy GEOdetic SATellite, GEOSAT, was launched on 12 March 1985, into an 800-km, 108-deg inclination orbit, carried an altimeter that was capable of measuring the distance from satellite to sea surface with a relative precision of about 5 cm. After a classified mission for the Navy, GEOSATs scientific Exact Repeat Mission (ERM) began on 8 November 1986 after it was manoeuvred into a seventeen-day repeat orbit.
