Exploring the hidden depths of space

• Completed
• Launched 17 November 1995
• Ended in 1998

The satellite made important studies of cool objects in the Universe that emit infrared radiation but no visible light. Infrared radiation is primarily heat, or thermal radiation. Even objects that we think of as being very cold (such as an ice cube) emit infrared radiation.

During its 28 months in orbit, the satellite completed 900 revolutions of the Earth and made 30,000 different scientific observations. Data from the mission is still being used by scientists today.

Mission facts

• ISO was originally designed to last 18 months but a combination of some world-class engineering and a bit of luck meant it actually lasted for 28 months, and generated far more data than expected.
  
  
• On average, ISO made 45 scientific observations each time it went around the Earth. Each orbit lasted just under 24 hours.
  
  
• To observe the cool part of the Universe, ISO's instruments needed to work at -269 °C, close to absolute zero (-273 °C). Scientists used a coolant of liquid helium to maintain these temperatures throughout the mission. This made ISO one of the coldest objects in the universe.
  
  
• The mission ended soon after the coolant ran out in April 1998. The satellite is now heading towards the Earth’s atmosphere, where it will burn up in about 2014.

Technology

Scientists from 11 European countries helped to design the four scientific instruments used by ISO.

A telescope with a 60 cm diameter primary mirror fed infrared light via a pyramidal mirror to the four instruments.

Between them, the instruments made observations at a wide range of wavelengths. This meant they could measure and produce images of many different types of astronomical object.

UK involvement

UK scientists led the development of one instrument and were involved in the development of three of the four instruments used by ISO. The STFC Rutherford Appleton Laboratory was involved in collating the data from the mission.