Corrections to Navigation of VEx/VMC images

This report outlines my contribution to the analysis of the navigation for images obtained with the Venus Monitoring Camera (VMC) onboard Venus Express (VEx). The navigation of the VMC images is carried out using the SPICE kernels generated for the VEX mission, and the SPICE kernels are read using NASA’s ICY routines. The navigation issues were examined both manually and automatically, using an IDL routine built for that purpose which will be described below. Only nadir and limb observations taken with the UV filter were examined in this work, discarding all the cases where the limb was not clearly visible. Apparent problems observed during the analyses of the images were the following: Pointing errors: when confronted the image and the coordinate grid obtained with the SPICE kernels, the match is not accurate enough in most of the cases. For this reason, in most of the images the planet’s coordinate grid appears slightly shifted relative to the planet disk. Grid Size errors: even after correcting the pointing mentioned in 1., sometimes the grid obtained with the SPICE kernels seems not to have the same size as the planet disk, being somewhat smaller in many cases and larger in others. Several cases are shown in the Appendix. This work was carried out by Javier Peralta (CAAUL/OAL, Portugal) at the Max Planck Institute for Solar System Research (Lindau, Germany) during May and June 2011. J. Peralta acknowledges a two-month contract by the German Max Planck Institute for Solar System Research and a Postdoctoral Fellowship from the Portuguese Fundação para a Ciência e a Tecnologia.