Optical-Performance Testing of the Laser RetroReflector for InSight

In the framework of the scientific activities foreseen by the NASA, ASI and INFN agreement for the InSight Mars lander mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport), we characterized the optical performance of the LaRRI instrument (Laser RetroReflector for InSight), through two sets of in-air solar-thermo-optical tests carried out at the SCF_Lab (Satellite/lunar/GNSS laser ranging/altimetry and cube/microsat Characterization Facilities Laboratory) of INFN–LNF in Frascati, Italy. The in-air tests consisted of optical and thermal measurements carried out by: (1) varying LaRRI’s bulk temperature (without solar illumination); (2) illuminating LaRRI with a solar spectrum; in both cases, LaRRI was interrogated with a laser at varying incidence angles w.r.t. its surface. This paper describes the tests and their results, which provide a first characterization of LaRRI’s optical and thermal behaviour in approximate Mars surface conditions.