Glass fiber reinforced plastics within the fringe and flexure tracker of LINC-NIRVANA

The Fringe and Flexure Tracking System (FFTS) is meant to monitor and correct atmospheric piston varia­ tion and instrumental vibrations and flexure during near-infrared interferometric image acquisition of LING­ NIRVANA. In close work with the adaptive optics system the FFTS enables homothetic imaging for the Large Binocular Telescope. One of the main problems we had to face is the connection between the cryogenic upper part of the instrument, e.g. detector head, and the lower ambient temperature part. In this ambient temperature part the moving stages are situated that move the detector head in the given field of view (FOV). We show how we solved this problem using the versatile material glass fiber reinforced plastics (GFRP's) and report in what way this material can be worked. We discuss in detail the exquisite characteristics of this material which we use to combine the cryogenic and ambient environments to a fully working system. The main characteristics that we focus on are the low temperature conduction and the tensile strength of the GFRP's. The low temperature conduction is needed to allow for a low heat-exchange between the cryogenic and ambient part whereas the tensile strength is needed to support heavy structures like the baffle motor and to allow for a minimum of flexure for the detector head. Additionally, we discuss the way we attached the GFRP to the remaining parts of the FFTS using a two component encapsulant.