Three on-board instruments turn Herschel’s telescope from a mere light collector into a pair of hi-tech eyes. The instrument detectors form the retina, where the light from astronomical objects is really seen. The instruments then detect and analyse the light in many different ways.

This artist’s impression shows the top view of the Herschel focal plane, with the focal plane units (FPUs) of the three scientific instruments: HIFI (Heterodyne Instrument for the Far Infrared), a high-resolution spectrometer, developed under the coordination of the SRON Netherlands Institute for Space Research; PACS (Photoconductor Array Camera and Spectrometer), developed under the coordination of the MPE, Germany; SPIRE (Spectral and Photometric Imaging REceiver), a camera, developed under the coordination of the Cardiff University (UK).

The three focal plane units are mounted on top of the optical bench inside the cryostat vacuum vessel, the top of which has been removed in this view to reveal the focal plane.