METIS opto-mechanical design & packaging study

METIS: "Mid-infrared ELT Imager and Spectrograph" is the mid-infrared (3 - 14 microns) instrument for imaging and spectroscopy for the European Extremely Large Telescope (E-ELT). To ensure high detection sensitivity the internal radiation of the instrument needs to be eliminated (sufficiently reduced) and thus needs to be operated at cryogenic temperatures. The instrument is divided in a cold and warm system. The cold system, the actual heart of the system, is subdivided into five main opto-mechanical modules located within a common cryostat (part of the warm system). The warm system provides the crucial environment for the cold system, including the instrument control and maintenance equipment. The end 2009 finished Phase-A study carried out within the framework of the ESO sponsored E-ELT instrumentation studies has been performed by an international consortium with institutes from Netherlands (PI: Bernhard Brandl - NOVA), Germany, France, United Kingdom and Belgium. During this conference various aspects of the METIS instrument (design) are presented in several papers, including the instrument concept and science case, and the system engineering and optical design. This paper describes the design constraints and key issues regarding the packaging of this complex cryogenic instrument. The design solutions to create a light, small and fully accessible instrument are discussed together with the specific subdivision of the cold and warm system to ensure concurrent development at various different institutes around Europe. In addition the paper addresses the design and development studies for the special, challenging units such as the large optical image de-rotator, the (2D) chopper mechanism and the special cryogenic drives.