Integral Satellite - International Gamma Ray Astrophysics Laboratory, Europe

The Integral satellite is the European Space Agency's (ESA) international gamma ray astrophysics laboratory, due for launch in October 2002. It is currently undergoing environmental tests at ESA's technical research centre in the Netherlands. The Integral spacecraft will have two gamma ray detectors: an imager and a spectrometer. Two monitor instruments support these instruments: an X-ray monitor and an optical camera. The operation will be controlled from the European Space Operations Centre (ESOC) in Darmstadt, Germany.

OBJECTIVES AND OPERATIONS OF THE INTEGRAL PROJECT

Integral will examine the remnants of supernovae explosions to learn more about how elements are formed. It will also study the sites of recent supernova explosions, and scientists speculate that it will find previously unknown supernovae remnants.

EUROPEAN SPACE OPERATIONS CENTRE (ESOC) AND GROUND STATIONS

The mission centre will be the European Space Operations Centre (ESOC) in Darmstadt, Germany, where the raw data will be gathered and turned into physical units. This data will be distributed to the observer and archived for later use by the scientific community. The satellite will be tracked from the ground stations Redu in Belgium (ESA) and Goldstone in the USA (NASA).

The satellite will go into an eccentric 72 hour orbit around the Earth at an altitude of 10,000-153,000km outside Earth's radiation belts to minimise background radiation effects. The inclination will be 51.6°. It will be launched in October 2002 on a Russian Proton rocket.

INTEGRAL SATELLITE

The spacecraft consists of a service module and a payload module. The service module provides the power generation, conditioning and control, stabilisation and ground-satellite link and the payload module hosts the instruments. The interface between the two modules was designed to be as simple as possible. This approach allows working in parallel on the service and payload modules, thereby reducing the time needed for developing, assembling and testing the spacecraft.

The orbit, power and data rates of Integral are very similar to ESA's XMM-Newton project, so the service module is a rebuild of the service module for that project. Electric power is generated by a deployable, double wing solar array and the energy is stored in two nickel-cadmium batteries. Hydrazine thrusters control the spacecraft. The new module varies from XMM-Newton in that the tanks are not internal and contain a diaphragm separating the liquid propellant from the pressurisation gas.

The payload module consists of an equipment platform accommodating the detector assemblies and an empty box supporting the 'upper floor' at a height of about 4m. The so-called coded masks, which remove nearly all background radiation are installed there. The backbone supporting the instruments in the payload module is an H-shaped structure. It is made of strong and stiff composite material and ensures that the instruments will have the structural stability necessary for their accurate pointing. The satellite is 5m high and has a diameter of 3.7m. It weighs 4.7t.

INSTRUMENTS ON THE INTEGRAL SATELLITE

Integral will have two gamma ray detectors: an imager and a spectrometer. These instruments are supported by two monitor instruments: an X-ray monitor and an optical camera. All four instruments are co-aligned and will observe the same region of the sky simultaneously. This allows the clear identification of gamma-ray sources, a key feature in studying high-energy processes in the violent universe.

The Spectrometer will gauge gamma ray energies with exceptional precision. It will be 100 times more sensitive than the previous high spectral resolution space instruments. It will perform spectral analysis of gamma ray point sources and extended regions over an energy range between 20keV and 8MeV with an unprecedented energy resolution of 2keV at 1MeV. This will be achieved by 19 hexagonal high-purity Germanium detectors.

CONTRACTORS ON THE INTEGRAL PROJECT

The lead contractor responsible for the design, integration and testing of the satellite is Alenia Aerospazio. 28 companies all over Europe are producing the many components for the different parts of the spacecraft. The total cost of the project excluding design and development of the servicing module, which is common with XMM-Newton, is €353 million.