A cold focal plane chopper for Herschel-PACS - critical components and reliability

Details A cold focal plane chopper for Herschel-PACS - critical components and reliability A cold focal plane chopper for Herschel-PACS - critical components and reliability

Sep 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001esasp.480..221h&link_type=abstract

In: Proceedings of the 9th European Space Mechanisms and Tribology Symposium, 19-21 September 2001, Liège, Belgium. Compiled by

Physics

Optics

Herschel Space Observatory, Choppers

Scientific paper

A chopper acts as an optical switch within the entrance optics of the PACS instrument onboard the ESA Space Observatory HERSCHEL to discriminate the light of faint celestial sources from a large background flux, which is basically due to the thermal radiation of the only moderately cooled 3.5m telescope (≍80K). This chopper primarily consists of a small electrically driven tilting mirror with a high position accuracy for the full range of elongations up to ±9° to be operated at 4K with a power dissipation of less than 4mW. At a chopping frequency of up to 10 Hz in square wave modulation scheme a duty cycle of 80% is to be achieved. After a pre-development phase at MPIA, which resulted in an optimized and cold tested prototype, the industrial optimization and implementation of the PACS chopper started in 2000 in a cooperation with the company Zeiss (Oberkochen). We focus on the new design of the chopper and its critical components, including the recently developed double-stage flexural pivots as high reliable bearings of the chopping mirror axis. The monolithic CuBe2 layout has to resist vibration loads of up to 45g during the launch of the ARIANE 5 carrier and to guarantee for an accurate motion in a cryogenic environment during a lifetime of at least 3 years in space, which corresponds to 630 Mio cycles of the chopper. Other components like the cryomotor and the rotor will be considered with respect to the selection of optimal materials, the reliability of mechanical linkages and the compensation of thermal stresses within the whole multi-material chopper assembly.

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