MIRI-JWST spectrometer main optics opto-mechanical design and prototyping

In December 2004 the European Consortium that develops the optical bench assembly for MIRI successfully passed the Preliminary Design Review. MIRI is the combined imager and integral field spectrometer for the 5-28 micron wavelength range under development for the JWST. After this PDR milestone the optical design of the MIRI spectrometer is now implemented in a compact, modular mechanical design that puts all optical elements in place within the required tolerances. Many aspects of this design are based on the heritage of previous instruments developed at ASTRON, in particular the cryogenic optics for the mid-IR VLT instruments VISIR and MIDI, but several adjustments to this design philosophy were made to develop the necessary space-qualified light-weighted components. Prototyping of these components has now started. This paper describes trade-offs and solutions for the opto-mechanical design of the optics (gratings, mirrors and their mountings) and of the main structure of the spectrometer, taking into account optical performance, manufacturability, cost and lead times. It also addresses the complex interface management in a large international consortium and reports first prototype results.