Prototyping of cryomechanisms for the JWST near-infrared spectrograph (NIRSpec)

In 2011 NASA and ESA plan to launch the James Webb Space Telescope (JWST) as dignified successor of the Hubble Space Telescope. Three scientific instruments will cover the wavelength regions in the near-infrared (0.6-5μm, NIRCam and NIRSpec) and in the mid-infrared (5-28μm, MIRI), respectively. The ESA-led multi-object spectrograph NIRSpec as major European contribution is presently entering the detailed design phase in a collaboration between European space industries, scientific institutes, ESA and NASA. To allow for various operational modes in the instrument’s optical train several cryo-mechanisms are required, i.e. wheels for exchanging optical elements like filters and gratings as well as linear actuators on refocusing mirrors. We will give an overview on the detailed design, the prototyping and the testing of those mechanisms comprising highest reliability in the cryo-vacuum (~ 35K) combined with minimal power dissipation (~ 5mW on average), ultimate position accuracy (~ 0.5 - 1arcsec) combined with high launch vibration capability (ARIANE 5, ~ 60g) and a very long lifetime (~ 15 years) for ground tests and space operation under various environmental conditions. To reach this goal in a low cost and risk approach we rely on the heritage from ESA's earlier infrared missions, i.e. ISO and HERSCHEL.