A determination of Earth equatorial ellipticity from seven months of Syncom 2 longitude drift

The 24-hour Syncom 2 satellite has been under periodic observation by range and range rate radar and Minitrack Radio Interferometer stations since mid-1963 [Wagner, 1964b]. Seven months of longitude drift in the vicinity of two momentarily stationary configurations were analyzed for sensitivity to hypothetical longitude components of the earth's gravity field which would be in ‘resonance’ on such a satellite [Blitzer et al., 1962; Wagner, 1964a]. This drift, in the region 54°W to 64°W (over Brazil), was derived from orbits calculated at the Goddard Space Flight Center. From mid-August 1963 to late November 1963, the figure-eight ground track of Syncom 2 drifted from 55°W to 59°W, with a mean acceleration of The average growth of the semimajor axis for this period was estimated as 0.0093±0.0042 km/day. The figure-eight configuration was momentarily stationary at about 54.76° on September 6, 1963, at which time the semimajor axis was 42166.0±0.2 km. On November 28, 1963, the westward drift of Syncom 2 was stopped by ground command firing of tangentially oriented cold gas jets on the satellite.