Optical performance of the wide-angle camera for the Rosetta mission: preliminary results

This report describes the preliminary experimental results obtained by the analysis of the optical performance of the Qualification Model of the Wide Angle Camera for the Rosetta mission. This camera is an F/5.6 all-reflecting telescope with a rather large 12 degree(s) X 12 degree(s) field of view that satisfies the scientific requirements about spatial resolution, contrast capability, and spectral coverage, thanks to an original two-mirror, off-axis and unobstructed optical design. Theoretically, from the simulation with a ray-tracing code, more than 80% of the collimated beam energy falls within a single pixel (20' X 20') over the whole camera field of view, and the possible contrast ratio is smaller than 1/1000. The analysis of the optical performance of the Qualification Model shows a good agreement between theoretical performance and experimental results. It's worth mentioning that this optical design is rather simple from a mechanical point of view, compact and relatively easy to be aligned. All these characteristics make this type of camera rather flexible and suitable also for other possible space missions in which similar performance are required.