Earth-Moon Mass Ratio from Mariner 9 Radio Tracking Data

Abstract

THE navigation of the Mariner 9 spacecraft from Earth to Mars was performed using phase-coherent range and doppler tracking data recorded by the Jet Propulsion Laboratory (JPL) Deep Space Network. These data also determine the Earth–Moon mass ratio, which involves the following physics: as the Earth revolves about the centre of mass of the Earth–Moon system, a sinusoidal curve is impressed on the range and doppler tracking data with a frequency equal to the sidereal mean motion of the Moon. This signature is shown in Fig. 1, where a perturbation of 0.0003 was made in the mass ratio (μ⁻¹ = mass of Earth over mass of Moon). This sinusoidal variation in the tracking data can be eliminated by finding a value for μ⁻¹ that properly represents the amplitude of the barycentre motion of the Earth. The procedure is direct and for all practical purposes is completely uncoupled from other parameters used in reducing the tracking data.