The Herschel-PACS grating drive mechanism: design status and prototype results

The Photodetector Array Camera and Spectrometer (PACS) is an imaging spectrometer-photometer which forms part of the science payload of the Herschel Space Observatory (formerly called FIRST), an ESA cornerstone mission (CS4) to be launched in 2007 on Ariane 5. This paper reports the present design of the motorised grating assembly for the PACS spectrometer. The PACS grating shall be capable of accurate positioning (4 arcsec) within a large angular throw (40 arcdeg) in cryogenic environment (4K). The drive mechanism is remotely controlled from the "Detector and Mechanism Controller" (DEC/MEC). Technologies of actuators, position sensors, pivots, lubricants, servo-control and cryogenic test set-up are discussed in this paper.