Research On Lunar Gravity Field Model And Its Applications

Lunar gravity field has a strong effect on lunar-orbiters. With a refined lunar gravity field, designers can design orbits better. Lunar gravity field is useful in calculating constants of lunar geodetic survey and geodynamics and researching lunar libration. With a detailed knowledge of the lunar gravity field, the lunar's mass center and moment of inertia can be determined accurately, so as to establish lunar geodetic coordinate system. Besides, as it is also the physical consequence of inner substance, we can learn more on lunar geologic evolving history and geologic structure.In this paper, through investigation of the latest lunar gravity field models, theories on lunar gravity field were analyzed, which include estimation methods of model, spatial and spectral characteristics of lunar disturbing gravity, correlation of lunar terrain and lunar gravity field. And the conditions and capability of lunar gravity field recovery were analyzed. The main works and innovations are as follows:1) A brief introduction was made on the Moon, its coordinate system, and its gravity field. The emphasis was laid on the characteristics of lunar gravity field that differ from the Earth's gravity field as well as the expression of lunar gravity field. Theories on the recovery of the lunar gravity field were reviewed, which involve dynamic models and solutions.2) The negative correlation of mascon terrain and gravity anomaly on lunar surface was studied. According to the tracking data of different models as well as by comparing the gravity anomaly of different models, RMS curves of the potential coefficients for models and Kaula curves, model quality was estimated. A method for model reliability analysis is proposed which estimates the model reliability by comparing the Signal-Noise Ratio of models that reflect the spatial frequency spectral signal and errors. Above all of these, a method of estimating lunar gravity field was proposed.3) The characteristics of the disturbing gravity with respect to height in the lunar gravity field were analyzed. And the effects of lunar disturbing gravity on spacecraft in low lunar orbit were discussed. By investigation of the spectral distributions of the radial spectral components with respect to height, the spectral sensitivities at different frequencies were estimated, and the relations between potential coefficients that can be sensed and orbiter heights were estimated. Furthermore, improvements were proposed to solutions to model coefficients of the low frequency, middle-frequency and high-frequency parts of the lunar gravity field.4) Requirements on resolutions for the recovery of certain degree and order model coefficient were determined, and the lowest requirements on longitudinal and latitudinal resolution were derived for the recovery of the lunar gravity field model up to different degree and order for a circular-polar lunar orbiter. Then discussions were made on "Chang' E" mission, and the effects of the selection of orbit parameters on the recovery of the lunar gravity field model were analyzed. Finally two methods were discussed for evaluation of the capability of lunar gravity field recovery using lunar orbiters.