Herschel payload: straylight design and performance

Abstract

Herschel is an ESA spaceborne far infrared observatory, to be launched late 2008. It's key science objectives emphasize specifically the formation of stars and Galaxies. The focal plane of the 3.5m diameter telescope is shared by three instruments located in the cryostat: PACS (imaging photometer and integral field line spectrometer, operating from 35µm to 205µm wavelength); SPIRE (imaging photometer and Mach-Zender interferometer, operating from 194µm to 572µm wavelength); and HIFI (heterodyne detector, from 157 to 625µm wavelength). Infrared straylight rejection is one of the key performances of the Herschel observatory. In this paper, we present the straylight requirements, some specific design issues, the estimated performances and test results.