The wide angle camera of the Rosetta mission: Design and manufacturing of a innovative baffling system for an aspherical optics telescope

Rosetta is the cornerstone mission of ESA devoted to the study of minor bodies of Solar System. The mission will be launched on January 2003 and has the rendez-vous with 46P/Wirtanen comet (on November 2011) as primary target. The final aim of the mission will be a better understanding of the formation and composition of early Solar System and of its evolution over the last 4.5 billion years. Rosetta has a complex instrumentation devoted both to remote sensing and to in situ investigation. The authors were involved in the design and manufacturing of the Wide Angle Camera (WAC) of the OSIRIS imaging system. The WAC has a very peculiar optical system based on two aspherical mirrors in an off axis configuration, and will be principally devoted to the study of the very faint gas and dust cometary features. To reach this goal an innovative baffling system was designed and constructed in order to obtain the stray-light suppression requirements for source both inside and outside the field of view of the camera. In particular a contrast ratio of 10-4 inside the field of view is needed in order to detect gaseous and dusty features close to the nucleus of the comet. In this paper the process of baffling design and manufacturing is described: the behavior of the baffle, previously calculated by numerical simulations from the mechanical and optical points of view, was assessed both for the single components and for the complete assembly as described in this paper.