Design, performances, and qualification of the optics of the Venus Spectrometer Instrument (VEM)

Abstract

In the frame of the two missions VERITAS (JPL/NASA) and EnVision (M5/ESA) to map Venus’ surface to determine the planet’s geologic history, an infrared spectro-imager (VEM) is developed under the responsibility of DLR in Berlin. The LIRA is responsible of the optical system of VEM, called VEMO. The concept is based on a filter made of multiple strips arranged side-by-side and positioned on a substrate. Each strip has its own optical bandwidth over the whole spectrum of 0.8-1.7μm. This filter is under the CNES responsibility, manufactured by Bertin-Winlight, Cilas working on the thin film deposition. The optical combination is made of three lenses, first acting as a telescope focusing on the filter, the two other lenses reimaging the filter on the detector through an aperture stop. This leads to a very robust and compact design with all the components installed in a mechanical barrel, with a large FoV of 41x35 square degrees. Facilities has been developed to test VEMO under various thermal conditions, over the whole optical bandwidth and FoV. First results of optical performances acquired in representative conditions are shown. A complete process of qualification is done for the mechanical and thermal environment (all the mechanical simulation done by MECANO-ID) on the whole objective, irradiation test is done only on optical samples.