Tests of LARES and CHAMP cube corner reflectors in simulated space environment

There are more than two thousands retroreflectors orbiting the Earth. Many are on geodetic satellites typically used for geodesy and geodynamics but also for testing fundamental physics such as in the case of the LARES and LAGEOS satellites. Other are mounted on GPS and GALILEO navigation satellites. Most retroreflectors are Cube Corner Reflectors (CCRs) that rely on the very accurate dihedral angles to return laser pulses towards the ground emitting stations. It is very important to know the thermal conditions of the CCRs and verify that the CCR dihedral angles are not deformed sensibly thus causing the return laser pulse to miss the station. To this aim it has been designed and built a specific thermovacuum chamber capable of reproducing the space environment by the use of 5 nitrogen cooled walls a Sun and Earth simulator and a vacuum enclosure that operates between 10(-6) and 10(-9) millibar. The chamber is equipped with several feedthrough for electrical signals and several optical windows. One of this is used for sending a laser beam inside the chamber. The beam will hit a CCR and will exit the chamber through the same window engaging an optical circuit for Far Field Diffraction Pattern acquisition. The paper will briefly address the LARES and CHAMP mission, describe the different designs of retroreflectors and in particular the ones of LARES and CHAMP and report the experimental results obtained on LARES and CHAMP CCR