  Herschel was launched on 14 May 2009, and is now an operational ESA space
observatory offering unprecedented observational capabilities in the
far-infrared and submillimetre spectral range 55-671 {\mu}m. Herschel carries a
3.5 metre diameter passively cooled Cassegrain telescope, which is the largest
of its kind and utilises a novel silicon carbide technology. The science
payload comprises three instruments: two direct detection cameras/medium
resolution spectrometers, PACS and SPIRE, and a very high-resolution heterodyne
spectrometer, HIFI, whose focal plane units are housed inside a superfluid
helium cryostat. Herschel is an observatory facility operated in partnership
among ESA, the instrument consortia, and NASA. The mission lifetime is
determined by the cryostat hold time. Nominally approximately 20,000 hours will
be available for astronomy, 32% is guaranteed time and the remainder is open to
the worldwide general astronomical community through a standard competitive
proposal procedure.
