Lunar gravity estimate: Independent confirmation

Abstract

Reduction of 2½ days of Lunar Orbiter 4 radio tracking data has provided an independent estimate of the low-degree spherical harmonic coefficients in the lunar potential model. The estimate is in good agreement with previous results and confirms that the moon is essentially homogeneous. These Doppler data, never incorporated in other gravity estimates, were obtained at relatively high spacecraft altitudes (2700–6000 km). This high-altitude data allowed the model to fit to the noise level of 1 mm/sec, unlike previous results, where systematic residuals of tens of millimeters per second occurred, owing to local gravity anomalies detectable at low spacecraft altitudes (≈100 km).