Interdisciplinary Development of the METimage Cryogenic Sub-System Thermo-Mechanical Design

METimage is a multispectral imaging optical instrument with a wide coverage realized by a scanning design. It is part of the instrument suite on satellite-type A of the Metrological Operational Satellite –Second Generation (MetOp-SG). The instrument covers a wide range of spectral bands from visible to long wave infrared split into 20 spectral channels. As the huge differences in wavelength exceed the capabilities of a single detector, the channels are distributed across three physically separated focal plane assemblies (FPA). To ensure the synchronized operation in a controlled stable thermal environment the Cryogenic Sub-System (CGSS) has been developed as the central sub-assembly of the METimage Instrument. This paper gives an overview of the design and verification methodologies used for the thermo-mechanical design of the CGSS considering the boundary conditions coming from the requirements of the different disciplines. The CGSS features a highly integrated design providing operational environment for three focal plane assemblies by means of active cooling to cryo-temperatures for the two infrared FPAs and a controlled environment for the third FPA (visible) operating at 300K. Cold and warm optical assemblies are linked by a set of beam splitters, folding mirrors and transmitting cryo-optics on a common highly stable structure. Due to the high level of integration, the system thermal design posed several challenges overcome by a sequential development process involving many disciplines: thermal design, structural design, optical design, electrical design, contamination control, parts materials and processes, AIT, alignment and performance engineering. Many design requirements defined by these disciplines lead to contradicting sizing requests and drive the design of each individual component within the cryogenic part of the CGSS. The selected design priorities, harmonization of interdisciplinary needs and verification approaches by analysis and successful test in an STM are described hereafter.