XMM-Newton (X-ray Multi Mirror) Space Telescope, International

The project centres on the development and launch into space of the XMM-Newton, an X-ray telescope. The XMM (X-ray Multi Mirror) will explore the universe for X-rays emitted by spectacular celestial sources, such as exploding stars and pulsars and astronomers hope that it will provide conclusive evidence of the existence of black holes.

The project sponsor was European Space Agency (ESA). The prime industrial contractor for the spacecraft is Dornier Satellitensysteme GmbH (DSS, Friedrichshafen), Germany, a member of DaimlerChrysler Aerospace AG (Dasa, Munich). Under DSS' industrial lead, over 35 companies were involved in building the spacecraft, which required an investment of $200 million (Euro 230 million).

LAUNCH VEHICLE

The launch vehicle was the Ariane 5, which injected the spacecraft into a transfer orbit. After just 29mins, XMM-Newton was released from the upper stage of the vehicle at a height of 2,350km. After a further minute, the communications signal of XMM was received. The XMM ground crew then sent the signal to unfold the crafts solar array with a 16.1m span and deploy the sunshield. After a few corrective manoeuvres over the course of 24hrs, the craft was then sent into its final high eccentric orbit (7,000km perigee/114,000km apogee).

On its 48-hour orbit the craft will rise to one-third the distance to the Moon. At this maximum distance (the apogee), the satellite travels slowly. But at its closest point, (the perigee) it passes 7 000km above the Earth and nine times faster. While in orbit, the telescope tube was emptied of any residual gases ('outgassing'), the sunshield was deployed and, the doors of the mirror modules were opened. The telescope is almost 11m in length, has a 4m diameter and a total mass of nearly 4t. It is the largest satellite ever built under ESA's science programme.

Similar to the colour of visible light, which provides important information on the temperature, composition and dynamics of cosmic objects, X-rays offer a wealth of chemical and physical data over a much wider energy range. XMM has a far better resolution than previous telescopes, thus will substantially advance the 'decoding' of X-ray sources. In a single day, XMM will detect more X-rays than the first US X-ray mission did 25 years ago in three years.

XMM-Newton carries three very advanced X-ray telescopes, each of which contain 58 high precision concentric mirrors, delicately nested to offer the largest collecting area possible to catch the elusive X-rays. The barrel-shaped mirror consists of two segments, with the first segment formed according to a paraboloid and the second to a hyperboloid mirror.

During its design stages, experts made sure that the XMM spacecraft incorporated a satellite bus as a separate module, so that it can also be used for further European research satellites.

SATELLITE TESTS AND ANALYSIS

DSS submitted the satellite test and analysis results to its customer, ESA. The tests included a space simulation test (at various temperatures and under vacuum conditions), vibration tests (to simulate the ascent loads during launch) and extensive functional checks.

A thermally and mechanically identical flight model was used for testing the integration procedure and proving the performance data under all load conditions of the satellite during launch and in space. For this to be performed, the spacecraft was transported to ESA's test centre in Noordwijk / Holland in September 1997, for conducting the load tests, as this is the only space simulation facility of such unique dimensions found in Europe.

During thermal vacuum tests, the equipment was placed in a vacuum chamber with a sun simulator. This was used to reproduce the intensity of sunlight, which recreated the environment of space with its extreme variations in temperature.

Vibration tests checked the strength of the outer casing and instruments on board. The spacecraft was progressively shaken at different strengths on a 'shaker', which created conditions up to 25% more severe than those expected at lift-off. The spacecraft resonance was also measured to evaluate how its different parts would react to set frequencies, including those that it would probably encounter at launch.

ACOUSTIC TESTS

The complete spacecraft was submitted in a reverberating chamber to very intense noise similar to which it would encounter during launch.