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Fact Sheet

 Fast Facts


Launch date: 17-Nov-1995 01:20 UT
Mission end: 16-May-1998
Launch vehicle: Ariane 44P launcher, Kourou
Launch mass: 2400 kg
Mission phase: Archive
Orbit: ISO was placed in a highly elliptical orbit with a perigee at around 1000 km; an apogee at 70 500 km; and a period of almost 24 hours.
Achievements: The discovery of water traces around the planets in our solar system and as far distant as the Orion Nebula
New views of star formation, previously hidden by dust

ESA's Infrared Space Observatory (ISO) is an astronomical satellite that was operational between November 1995 and May 1998. It operated at wavelengths from 2.5 to 240 microns, in the infrared range of the electromagnetic spectrum. Because the atmosphere acts as an 'umbrella' for most infrared wavelengths -preventing them from reaching the ground- a space telescope is needed to detect this kind of radiation invisible to the human eye and to optical telescopes.

Mission Objectives

ISO was able to make chemical diagnoses of celestial objects including planets, comets and stars, as close to home as our own solar system and as far distant as other galaxies. Many new discoveries have been made as a result of ISO's data, and are still being made today.

Mission Name

ISO stands for Infrared Space Observatory.


The ISO satellite essentially consisted of the following:

  • Large liquid-helium cryostat
  • Telescope with a 60-cm diameter primary mirror
  • Four scientific instruments
  • Service module
Height 5.3 m
Width 3.6 m
Depth 2.8 m
Launch mass 2400 kg


ISOCAM Covering the 2.5-17 micron band with two different detectors
ISOPHOT  Operating at a broad range of wavelengths between 2.5 and 240 mcirons
SWS Covering the 2.4 to 45 micron band
LWS Operating at the 45 to 196.8 micron band


ISO's highly elliptical orbit had:

  • Perigee at around 1000 km;
  • Apogee at 70 500 km
  • Period of almost 24 hours.

The lowest parts of the orbit lay inside the Earth's van Allen belts of trapped electrons and protons. Inside these regions ISO's detectors were scientifically unusable due to effects caused by radiation impacts. ISO spent almost 17 hours per day outside the radiation belts and during this time all detectors could be operated.

Operations Centre

The Science Operations Centre at ESA's Satellite Tracking Station at Villafranca (Spain) was responsible for the control of the satellite. This is also where observations were scheduled. However, for scientific use ISO needed to be in continuous contact with a ground station. NASA's station at Goldstone (US) tracked ISO when it was obscured from Villafranca by the Earth.

Last Update: 1 September 2019
16-Jul-2024 00:48 UT

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