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The importance of an accurate model of the Moon gravity field has been assessed for future navigation missions orbiting and/or landing on the Moon, in order to use our natural satellite as an intermediate base for next solar system observations and exploration as well as for lunar resources mapping and exploitation. One of the main scientific goals of MAGIA mission, whose Phase A study has been recently funded by the Italian Space Agency (ASI), is the mapping of lunar gravitational anomalies, and in particular those on the hidden side of the Moon, with an accuracy of 1 mGal RMS at lunar surface in the global solution of the gravitational field up to degree and order 80. MAGIA gravimetric experiment is performed into two phases: the first one, along which the main satellite shall perform remote sensing of the Moon surface, foresees the use of Precise Orbit Determination (POD) data available from ground tracking of the main satellite for the determination of the long wavelength components of gravitational field. Improvement in the accuracy of POD results are expected by the use of ISA, the Italian accelerometer on board the main satellite. Additional gravitational data from recent missions, like Kaguya/Selene, could be used in order to enhance the accuracy of such results. In the second phase the medium/short wavelength components of gravitational field shall be obtained through a low-to-low (GRACE-like) Satellite-to-Satellite Tracking (SST) experiment. POD data shall be acquired during the whole mission duration, while the SST data shall be available after the remote sensing phase, when the sub-satellite shall be released from the main one and both satellites shall be left in a free-fall dynamics in the gravity field of the Moon. SST range-rate data between the two satellites shall be measured through an inter-satellite link with accuracy compliant with current state of art space qualified technology. SST processing and gravitational anomalies retrieval shall benefit from a second ISA accelerometer on the sub-satellite in order to decouple lunar gravitational signal from other accelerations. Experiment performance analysis shows that the stated scientific requirements can be achieved with a low mass and low cost sub-satellite, with a SST gravimetric mission of just few months. [ABSTRACT FROM AUTHOR]

Abstract: The gravitational anomalies of the Moon have never been completely mapped; in particular, those on the hidden side are known only through the interpolation of data obtained for the visible side. Many space agencies around the world are developing new plans for the exploration of the Moon, hence a more precise knowledge of lunar harmonics could be useful for the planning of future missions. The aim of this study is to demonstrate the feasibility of a micro-satellite mission for the accurate mapping of high order lunar harmonics, generated by density anomalies, on the hidden side of the Moon. The mission, conceived within the School of Aerospace Engineering, at the University of Rome “La Sapienza”, employs two small probes (whose masses will be under 100kg), placed in two orbits around the Moon, with a fixed ratio between their orbital periods. The main probe will essentially be a relay satellite placed in a higher and eccentric orbit, always facing the Earth; a smaller probe will be in a low circular, near-polar, orbit. A reference signal would be sent from a net of Earth stations, and relayed by the relay satellite to the smaller probe, that reflects the signal back to the relay satellite, and then to Earth. A subsequent analysis of the Doppler effect on the downlink signal, with respect to the uplink, will allow to build a map of Moon gravitational field. The interesting aspect of this method of measurement is that there is no need to carry any kind of instrumentation for Doppler effect detection, including a stable frequency reference, on board. This allows the reduction of overall costs and technical complexity of the mission. The encouraging results of this study show the possibility of the realization of the mission in the short term, and with a limited budget, given the collaboration between universities, the aerospace industry, and any space agency. [Copyright &y& Elsevier]