Proceedings Article | 12 July 2023
KEYWORDS: Collimators, Mirrors, Equipment, Optical alignment, Manufacturing, Vacuum chambers, Light sources and illumination, Design and modelling, Astronomical imaging, Black bodies
The Meteosat Third Generation is the new generation of European operational geostationary meteorological system. The MTG series will comprise 4 imaging (MTG-I) and 2 sounding (MTG-S) satellites. The MTG-S sounding satellites, whose development is led by OHB System (Wessling, Germany), will carry 2 instruments: an Infrared Sounder (IRS) and an Ultraviolet Visible Near-Infrared spectrometer (UVN). The aim of IRS instrument is to provide detailed vertical profiles of atmospheric temperature and water vapor at a high spatial resolution of 4km. These data will be used in the future for numerical weather prediction and nowcasting. In the framework of this project, AMOS (Liège, Belgium), as a subcontractor of OHB, is the responsible for the design, manufacturing, integration, alignment and testing of the Geometrical and Spectral Test Assembly (GESTA) for the performance tests and calibration if the IRS under operational conditions. GESTA is an Optical Ground Support Equipment (OGSE) used for optical measurements during the alignment and test phases of the Infra-Red Sounder (IRS) instruments. The GESTA is composed of three different main subassemblies: The source Assembly (SA), designed by Bertin Technologies (Aix-en-Provence, France) is composed of a heated pattern plate mounted on an XY translation stage enabling to position it across the focal plane of the collimator. A Cold Black Body, operated at 90K, ensures the necessary contrast for the geometrical measurements. An Integrated Sphere is fed with MWIR and LWIR laser outputs, which are located outside of the vacuum chamber, and hence generates a uniform monochromatic output towards the collimator and ultimately the IRS. The Gas Cell, designed by Centre Spatial de Liège (CSL – Liège, Belgium), consists of a Hot Black Body, operated at high temperature (295K, 523K), as broad-band MWIR/LWIR light source and an atmospheric gas cell, operated at 293K with the possibility to fill it with up to 4 different gases in order to check the spectral and radiometric sensitivities of the IRS. The collimator, designed by AMOS, consists in a four mirror anastigmatic telescope with focal length of 2600 mm and an entrance pupil size of 320mm, operated at ambient temperature (293K). The collimator mirrors are made out of light-weighted aluminum structure with gold coating. The mirrors are mounted on a baseplate, which is of the same material and allows low stresses and deformations due to differential thermal dilatation. In view of its qualification, GESTA underwent an extensive testing campaign including thermal control performances, alignment stability and radiometric performances under operational conditions (i.e. same conditions as the ones encountered with the IRS instrument in front of GESTA). The results of the tests allow to demonstrate the compliance of the GESTA OGSE to the requirements. Additional presentation content can be accessed on the supplemental content page.
