Determination and Uncertainty Analysis of Mercury Libration Using BepiColombo HRIC Images

BepiColombo is an upcoming joint ESA/JAXA mission to Mercury. In particular the High Spatial Resolution Camera (HRIC), part of the SIMBIO-SYS (Spectrometer and Imagers for MPO Bepicolombo Integrated Observatory - SYStem) instrument suite, will characterize in detail the surface of the planet. In this work the BepiColombo rotation experiment is analysed: goal of the experiment is to investigate Mercury's interior measuring its rotational state. In this experiment images of surface regions taken at different epochs are used to retrieve information on Mercury's rotation and libration parameters. This analysis requires the use of an accurate model of the rotation of Mercury, to correlate the position of observed landmarks with planet libration. Then model parameters can be derived from observations using a maximum likelihood estimator. Uncertainties on spacecraft position, spacecraft attitude, imaged landmark position and camera intrinsic parameters result in the overall uncertainty on the estimated parameters. Simulations of the experiment and uncertainty analysis show that, with a small number of landmarks/images, the total planet libration can be measured. This analysis provides also support for the better design of the experiment in order to attain its scientific goals.