The figure of Mars and its effect on radar-ranging.

Formulae are given which indicate the errors made in computing the radar-range to a planet when one assumes the planet to have a spherical surface, centered at the center of mass. These formulae are evaluated for Mars, using an ellipsoidal fit of the martian surface obtained from the occultation measurements of the Mariner 9 spacecraft. The secularlike part of the errors amounts to about 4 km in range over the past 3 oppositions, due mainly to the flattening of 0.006 and to a 3 km southerly displacement of the center of figure from the center of mass. The method of solution is given in the appendix along with a method for applying the ellipsoidal model to the reduction of radar-range data.