The Integral mission launches from the Baikonur spaceport. Image: ESA-S. Corvaja, Oct 2002 The European Space Agency (ESA) launched the Integral satellite on 17 October 2002. A Russian Proton rocket carried the probe into space from the Baikonur cosmodrome in Kazakhstan.

Integral is ESA’s first gamma ray observatory. The primary mission has been extended until 2007.

Gamma rays are the most energetic part of the spectrum of electromagnetic radiation, which includes visible light and radio waves. At such high energies there are few individual wave-particles (photons) so telescopes need to observe many sources for long periods of time.

The high energy of gamma rays makes them dangerous, but fortunately our thick atmosphere absorbs them so shields the surface of the Earth and protects life.

Integral orbits the Earth every three days, spending most of its time at altitudes of more than 40,000 km. This places the mission well above the Earth’s radiation belts so their background contribution is removed.

The spacecraft

Artist’s impression of the Integral spacecraft in Earth orbit. Copyright: ESA. Illustration by D. Ducros Integral is around 5 metres high and weighs more than 4 tonnes. The satellite divides into a service module (a replica of the one on XMM-Newton) and a payload module that carries the scientific instruments.

The instruments weigh 2 tonnes, making them the heaviest payload ever launched by ESA. Two devices detect gamma rays. Firstly, an imager will give the sharpest-ever images made in this region of the spectrum. Secondly, a spectrometer will measure the energies of incoming gamma-ray photons. Alongside these, an X-ray monitor and optical camera will assist in identifying the gamma-ray sources.

4 metres above the other instruments is a platform with a 'coded mask’, essentially a pinhole camera with many different holes. Gamma-rays cannot be focussed so the coded mask is used to identify the direction of incoming radiation and to build up an image.

Mission objectives

Images of the Cygnus X-1 region from Integral’s four detectors are superimposed on an artist’s impression of the black hole and companion star. Copyright: ESA. Illustration by the Integral team & ESA/ECF Gamma rays are emitted by some of the most energetic objects in the Universe. These include exploding stars (supernovae), material falling into black holes and the enigmatic gamma-ray bursts (GRBs). Integral began its studies in earnest in early 2003 and has already returned its first results.

First light

GRB observed by Integral on 25 November 2002. The image of the event is in the central frame and an artist’s impression can be seen on the upper left. The GRB lasted just 20 seconds, was designated GRB021125 and is thought to be at a distance of 5 billion light years from our galaxy. Copyright: ESA. Illustration by the Integral SPI Team & ESA/ECF Integral observed the high-energy radiation source Cygnus X-1 in the autumn of 2002. Cygnus X-1 is thought to be a black hole with five times the mass of our Sun slowly devouring its blue giant companion star. The star (HDE 226868) has a surface temperature of 31000 K and orbits the black hole every 5.6 days. 

During its initial investigations, Integral also managed to detect its first GRB. These outbursts will be a key target over the lifetime of the mission.