Perturbations in perigee and eccentricity at the critical inclination

A cluster of three satellites showed large, unpredicted orbital perturbations shortly after launch. There was immediate concern for the success of its mission which depends on the stability of the cluster geometry. The Naval Surface Weapons Center found the zonal harmonics of degree five and seven to cause most of the observed perturbations. Subsequently, the three orbits were computed for the time frame June 1976 to July 1984. It was also shown that the cluster configuration remains unaffected by the large orbital perturbations, and the mission appears safe.