Reliability oriented design and testing of a telescope's front cover for long life space mission

The reliability of a telescope's front cover constitutes its primary demand, not to compromise the functionality of the whole instrument. From this point of view the design of the mechanism and the testing campaign should prove its fulfillment to the performance requirements, and its insensitivity to the environmental conditions, particularly for a long life mission where the performances have to be guaranteed along the whole life of the experiment. The Front Door Mechanism for the WAC (Wide Angle Camera) and NAC (Narrow angle Camera) telescopes constituting the OSIRIS experiment of the ROSETTA mission has been optimized to minimize the loads acting during its functional phases and the loads transferred to the other components of the optical bench, but at the same time to bear the loads acting during the launch and in the operating environment. The test campaign performed to demonstrate the compliancy of the mechanism to the requirements included environmental tests such as vibration and thermal vacuum cycling, life test, measurement of the resistant torque and of the reliability of the housekeeping sensors, and proved the fulfillment of the device to the requirements in terms of performances and insensitivity to the environmental tests performed. The life test executed during the thermal cycling proved the capacity of the mechanism to maintain its characteristics all along the number of activations foreseen for the test, being also unaffected by the temperature variations within the operating range.