page_title: Infrared Space Observatory
section_title: The satellite
hierarchical_section_title: Infrared Space Observatory / The satellite
caption_attribution_description: English: Animation of Infrared Space Observatory's orbit&#160;&#160;&#160;&#160;&#160;&#160; Infrared Space Observatory&#160;· &#160;&#160;&#160;&#160;&#160;&#160; Earth
context_page_description: The Infrared Space Observatory was a space telescope for infrared light designed and operated by the European Space Agency, in cooperation with ISAS and NASA. The ISO was designed to study infrared light at wavelengths of 2.5 to 240 micrometres and operated from 1995 to 1998.
  The €480.1-million satellite was launched on 17 November 1995 from the ELA-2 launch pad at the Guiana Space Centre near Kourou in French Guiana. The launch vehicle, an Ariane 44P rocket, placed ISO successfully into a highly elliptical geocentric orbit, completing one revolution around the Earth every 24 hours. The primary mirror of its Ritchey-Chrétien telescope measured 60 cm in diameter and was cooled to 1.7 kelvins by means of superfluid helium. The ISO satellite contained four instruments that allowed for imaging and photometry from 2.5 to 240 micrometres and spectroscopy from 2.5 to 196.8 micrometers.
  Currently, ESA and IPAC continue efforts to improve the data pipelines and specialized software analysis tools to yield the best quality calibration and data reduction methods from the mission. IPAC supports ISO observers and data archive users through in-house visits and workshops.
context_section_description: The basic design of ISO was strongly influenced by that of its immediate predecessor. Like IRAS, ISO was composed of two major components:
  Payload module, composed of a large cryostat holding the telescope and the four scientific instruments.
  Service module, supports the activities of the payload module by providing electrical power, thermal control, attitude and orbit control and telecommunications.
  The payload module also held a conical sun shade, to prevent stray light from reaching the telescope, and two large star trackers. The latter were part of the Attitude and Orbit Control Subsystem (AOCS) which provided three-axis stabilisation of ISO with a pointing accuracy of one arc second. It consisted of Sun and Earth sensors, the before-mentioned star trackers, a quadrant star sensor on the telescope axis, gyroscopes and reaction wheels. A complementary reaction control system (RCS), using hydrazine propellant, was responsible for orbital direction and finetuning shortly after launch. The complete satellite weighed just under 2500 kg, was 5.3 m high, 3.6 m wide and measured 2.3 m in depth.
  The service module held all the warm electronics, the hydrazine propellant tank and provided up to 600 watts of electrical power by means of solar cells mounted on the sunpointing side of the service module-mounted sunshield. The underside of the service module sported a load-bearing, ring shaped, physical interface for the launch vehicle.
  The cryostat of the payload module surrounded the telescope and science instrument with a large dewar containing a toroidal tank loaded with 2268 litres of superfluid helium. Cooling by slow evaporation of the helium kept the temperature of the telescope below 3.4 K and the science instruments below 1.9 K. These very low temperatures were required for the scientific instruments to be sensitive enough to detect the small amount of infrared radiation from cosmic sources. Without this extreme cooling, the telescope and instruments would see only their own intense infrared emissions rather than the faint ones from afar.
caption: Animation of Infrared Space Observatory's orbit
     Infrared Space Observatory ·    Earth