Meeting Report: BSRL/JPL Seminar on the Lunar Motion

Abstract

mination of the selenodetic coordinates of surface features from the analysis of Lunar Orbiter photographs. The consistency of the results from different frames and different spacecraft is used as a measure of the accuracy of the techniques used. The present inconsistencies are on the order of 2 km, as a result of several improvements in the analysis. The 'periwiggle problem' that has plagued the data analyses of the Lunar Orbiter trajectories was the subject of a discussion by Gayle D. Barrow and Phillip E. Hong, Boeing Space Division. The periwiggle is a high-frequency systematic fluctuation in the doppler residuals of the spacecraft trajectory in the vicinity of the periapse, implying unexplainable excursions of perhaps as much as 60 m from the nominal orbit. An analysis of the residuals as a function of periapse altitude indicates that the cause might be correlated with lunar surface features. Fourier analysis of the residuals from both real and simulated data showed significant differences near periapse, but not in the rest of the orbit. No correlation could be found between the Fourier characteristics and possible missing frequencies in the harmonic expansion of the potential function. Paul M. Muller and Wm. L. Sjogren, Jet Propulsion Laboratory, followed this discussion by describing their discovery of a one-to-one correlation between large positive gravity anomalies and the ringed maria. Lunar Orbiter data were used to construct a gravimetric map of the visible face of the Moon. From this map, it was concluded (Muller and Sjogren, 1968) that each of the ringed maria contains a high-density mass concentration buried perhaps I00 km below the surface, such as, might be the result of the impact of a nickel-iron asteroid. This paper generated the most spirited discussion of the meeting. Muller emphasized that their findings, while qualitatively sound, could not be expected to be quantitatively reliable, nor do they prove that the ringed maria are impact features. The lunar potential field was treated by P. Sconzo, IBM, as a Helmert surface of