Thermal deformation on a laser retro-reflector of LARES satellite: error analysis

LARES is an Italian Space Agency satellite that was successfully put in orbit with the qualification launch of VEGA. The surface of the satellite is covered with 92 Cube Corner Reflectors (CCRs) that allow its precise positioning through the measurements of the International Laser Ranging Service. By measuring the time of flight of the laser pulses sent towards the satellite it is possible to reach ranging accuracies of few millimeters from the best stations. LARES is passive and as such it does not have thermal control. Thermal deformations of the CCRs can be calculated if power input, boundary conditions and thermal heat transfer parameters are known. The reflecting performances of CCRs are typically evaluated through the analysis of the Far Field Diffraction Pattern (FFDP) which provides information on the energy distribution, of the reflected laser pulse, on the ground. The CCR deformations can change the FFDP thus reducing the probability to have good laser returns to the station. Due to its particular CCR mounting system, that minimizes contact with the CCR, heat transfer of the CCR is mainly governed by radiation. It is therefore important to evaluate experimentally the solar absorptivity α_s and the infrared emissivity ε. The paper will report the error analysis to provide guidelines for an optimized test.