1.2. Background

The Herschel Space Observatory is an ESA cornerstone mission, for high spatial resolution observations in the FIR and sub-millimeter regime, launched on the 14th of May 2009 aboard an Ariane 5 rocket together with Planck. It was placed on a Lissajous 700 000 km diameter orbit 1.5 million kilometers away from Earth at the second Lagrange point of the Earth-Sun system.

The mission is named after Sir William Herschel, who discovered the infrared radiation in 1800.

It is the first space observatory to cover the full far-infrared and submillimetre waveband. It performs photometry and spectroscopy in the 55-670 µm range, with its 3.5m diameter radiatively cooled telescope, with three science instruments housed inside a superfluid helium cryostat.

Herschel is designed to observe the "cool universe". The main scientific objectives of the mission are:

Herschel is operated as an observatory facility for three years of routine observations. Roughly two thirds of the observing time are "open time", and will be offered through a standard competitive proposal procedure.

The Photodetector Array Camera & Spectrometer (PACS) is one of the three science instruments of the Herschel observatory. PACS provides the Herschel Space Telescope with the capabilities for spectroscopy and imaging/photometry in the 55-210 µm range.

PACS has been designed and built by a consortium of institutes and university departments from across Europe under the leadership of the Principal Investigator Albrecht Poglitsch at Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany. Consortium members are from Austria: UVIE; from Belgium: IMEC, KUL, CSL; from France: CEA, OAMP; from Germany: MPE, MPIA; from Italy: IFSI, OAP/OAT, OAA/CAISMI, LENS, SISSA; from Spain: IAC.

For a detailed description of the PACS instrument and its in-flight performances, we refer to Poglitch et al., (2010).