ISO was the world's first true orbiting infrared observatory
(Figure 1.1). It
was given a perfect launch on 17
November 1995 by an Ariane IV vehicle. Equipped
with four sophisticated and versatile scientific instruments, it
provided astronomers with a facility of unprecedented sensitivity and
capabilities for an exploration of the universe at infrared wavelengths
from 2.5 to 240
m. The satellite was a great technical and
scientific success with most of its sub-systems operating far better
than their specifications and with its scientific results impacting
practically all fields of astronomy. At a wavelength of 12m,
ISO was one thousand times more sensitive and had one hundred times
better angular resolution than its predecessor, the all-sky-surveying
IRAS1.1.
During its routine Operational Phase (4 February 1996 to 8 April 1998), which lasted almost a year longer than specified, ISO successfully made over 27000 individual scientific observations and more than 4000 calibration observations.
After termination of in-orbit operations, all observations were re-processed with the `end-of-mission' calibration and pipeline. The ISO Data Archive opened to the world-wide astronomical community in December 1998 and all data had entered the public domain by August 1999. At the beginning of 2002, the data were again re-processed with the `end-of-post-mission' calibration (final off-line processing software OLP Version 10) to create the ISO Legacy Archive.
ISO's Post-Operations Phase (POPS, 1998 - 2001) was designed to leave behind a homogeneous archive with improved calibration as a legacy to future generations of astronomers. From 2002 to 2006, an Active Archive Phase (AAP) takes place with the goal of maximising the scientific exploitation of ISO's vast data sets. In this latter period, the archive will be brought into its final form, including the concept of feeding back into the archive data reduced `by hand' by experts (the so-called Highly Processed Data Products or HPDPs).
