Lunar Reference Systems

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The goal of this project is to realize Moon-related systems consistently tied to the ITRS/ICRS, a prerequisite for further lunar science and exploration. This project also paves the way for transferring established geodetic methods for mapping of extra-terrestrial bodies. In the first period, basic concepts have been developed: We have improved LLR analysis and modelling, e.g. by an added ground and reflector station, as well as taking tidal displacements of lunar reflectors into account. We re-analysed the LLR data set including all currently available LLR normal points. Through simulations, we showed the benefit of novel reflector types. We have demonstrated how photographs of landing sites can be combined with LRO images to generate highly accurate local maps stabilised by the LLR reflector coordinates. We have developed techniques for LRO orbit determination based on different types of tracking data. In the second funding phase, these methods shall be further extended, e.g. by using LOLA crossovers or novel data from D-VLBI. The major objectives are to refine realisations of the lunar reference system, consistently embedded into the ICRF. This will be achieved by taking different measures:1) Realise LLR modelling with mm-level of accuracy. Refinement of models affecting lunar motion and rotation, e.g. external and internal torques, will further improve the LLR retroreflectors¿ coordinates as point-wise realisations of the lunar reference system.2) Reconstruct precise LRO orbits from multiple data sets. An independent capability for combined determination of orbits and low-degree harmonics of lunar gravity shall be established, using radiometric as well as LRO one-way laser tracking and altimetric data.3) Integrating novel data from missions LRO and GRAIL. We will develop a capability in Germany, independent from NASA, for referencing LRO altimetry and imagery to the lunar system, and contributing to improved physical parameters of the Moon. At the end of project, we will be able to analyse data from other orbiter missions.4) Data combinations. Combinations of LROC images and LOLA altimetry will lay the basis for accurately mapping the Moon. LROC images are combined with images from former lunar missions and tied to the LLR reflector coordinates. In the polar regions, accurate DTMs from LOLA will be the basis for generating illumination maps, which will be valuable for future landing missions, to identify places with the longest possible daylight hours.5) New solutions of the lunar reference system. A concept for the combination of LLR with VLBI observations will be developed by analysing simulated and, if possible, real differential VLBI measurements between radio transmitters on the Moon and quasars. As a major result, the current realisation of the selenocentric system will be improved to achieve accurate and Moon-wide uniform coordinate knowledge and a high-resolution lunar map. This lunar frame will be firmly tied to the ICRF and ITRF.