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.

Credits: ESA

HIFI is a very high-resolution heterodyne spectrometer. The heterodyne detection principle involves translating the frequency range of the signal observed by the telescope to a lower frequency where it is easier to perform the required measurements.

This is done by mixing the incoming signal with a very stable monochromatic signal, generated by a local oscillator, and extracting the difference frequency for further processing.

HIFI observes in seven bands covering 480 to 1910 gigaHertz.

It was developed by a consortium led by SRON Netherlands Institute for Space Science.

Credits: ESA

The opening of this infrared window by PACS to sensitive photometry and spectroscopy at high spatial resolution will address a wide range of key questions of current astrophysics concerning the origins of stars, planetary systems, galaxies, and the evolution of the Universe.

PACS contains four detector arrays, two bolometer arrays and two Germanium:Gallium photoconductor arrays. The bolometer arrays are dedicated for wideband photometry, while the photoconductor arrays are to be employed exclusively for medium-resolution spectroscopy. PACS can be operated either as an imaging photometer, or as an integral field line spectrometer.

It was developed by a consortium led by Max-Planck-Institut für extraterrestrische Physik, Germany.

Credits: ESA

These observations will help tackle two of the most fundamental questions in astronomy: how and when did galaxies form and how do stars form?

The three-band imaging photometer is centred at 250, 350 and 500 micrometres, and an imaging Fourier Transform Spectrometer (FTS) covering 200-670 micrometres. The detectors are arrays of feedhorn-coupled NTD spider-web bolometers cooled to 0.3 K. SPIRE was developed by a consortium led by Cardiff University (UK).

Credits: ESA