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:
to study the formation of galaxies in the early universe and their subsequent evolution;
to investigate the formation of stars and their interaction with the interstellar medium;
to observe the chemical composition of the atmospheres and surfaces of comets, asteroids, planets and satellites;
to examine the molecular chemistry of the universe.
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).