Since its launch on May 14th 2009 Herschel is the largest telescope of its kind in space. Herschel's 3.5-metre diameter mirror collects long-wavelength infrared radiation from some of the coldest and most distant objects in the Universe. Herschel is the only space observatory to cover the spectral range from far-infrared to sub-millimetre wavelengths. The Herschel satellite is 7.5 metres high and 4 metres wide, with a launch mass of approximately 3.3 tonnes. The bulk of the spacecraft consists of a superfluid liquid helium cryostat inside which three scientific instruments (PACS, SPIRE & HIFI) are operated. Via various cooling stages the instruments are cooled to between a few tens and a few tenths of a degree above absolute zero. This paper gives a brief overview of the spacecraft and the on-ground testing, with an emphasis on the cryogenic issues encountered.

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