Planck is in Liège!

At the end of 2008, or perhaps early in 2009, the European space program will launch Herschel and Planck, two satellites designed to make scientific observations, into space with the help of powerful Ariane 5 rockets. Their mission is to probe the mysteries of the universe, such as the formation of galaxies, and to gather new information bearing on the origin and expansion of the universe by investigating the traces left by the initial explosion known as the Big Bang. In conducting these tests in a simulated outer space (vacuum and ultra-low temperature) environment, the CSL (Liège Space Center) will be playing a key role in the success of both satellite launch missions.

Planck-artistHerschel and Planck, (*) whose instruments have to be able to function in ultra-cold temperatures, will be placed in stationary orbits 1.5 million kilometers from Earth, a distance four times as great as that between the Earth and the moon. They will be installed at Lagrangian point L2, one of several points where gravitational equilibrium between the Sun and the Earth can be achieved (L2 actually keeps the Earth between it and the Sun), and they will observe the cosmos from there. Both satellites are being launched into space by the ESA (European Space Agency) on behalf of the scientific community.

The two missions are costing a total of 2 billion euros, half of which represents the cost of the satellite packages alone, but their missions are of the highest scientific interest. The director of the CSL until 2010, Jean-Marc Defise, is aware of the importance of the cryogenic tests to be carried out in his laboratory complex, which is one of the few in Europe that could perform them on such large objects as these satellites.

In the testing for the complete Planck observatory satellite launch module (without solar panels), Defise sees the ultimate validation of the technological efforts that the University, supported by the Belgian government via the Federal agency for scientific policy, has undertaken in response to the needs of the ESA. For him, these are new proofs of the excellence and the sterling reputation of the Liège facility and the expertise of its scientists in the area of space research.

A technological “first”

Financed by the Member States of the ESA (European Space Agency), Herschel (3.3 ton payload at launch) and Planck (1.8 tons) were built on the same platform by cooperating European industries, under the direction of the company Thales Alenia Space. This company’s affiliate ETCA in Charleroi worked on power conditioning units for the project, and the Nivelles firm EHP (Euro Heat Pipes ; member of WSL, Wallonia Space Logistics) provided the heat conduction pipes. But the know-how of the CSL was required for the tasks of estimating and calibrating the payload for Herschel – a monolithic telescope with a diameter of 3.5 meters – in the vertical space environment simulator FOCAL 6.5 (**). The three instruments in the focal plane of the satellite were also been tested for their abilty to withstand vibration under cryogenic conditions by the CSL, by means of a unique installation designed by Liège technicians. Now it is Planck’s turn to undergo testing in the horizontal simulator FOCAL 5 : the object of this series of tests, the last before the module is transferred to the Guiana Space Center (CSG) at Kourou, is to verify that the instrumentation for the 1.5 meter telescope functions perfectly under the ultra-cold conditions it will encounter in outer space.

The flight model for the Planck European observatory was transferred via special convoy from ESTEC, the European center for space research and technology in Noordwijk, the Netherlands, and arrived on April 23. This was the third time it had visited Liège: a prototype was tested during 65 days in an airless environment in 2005, and part of the flight model came to Liège in the first half of 2006 for 21 days of testing. Performance testing for the optical mirrors of Planck’s telescope took place separately at the CSL under ultra-cold conditions, using instrumentation specially designed by Liège technicians. These mirrors were tested before being mounted in the telescope, which focuses signals received toward complex cone-shaped detectors.

(*) These are two great names from the European scientific pantheon: the astronomer William Herschel (1738-1822) discovered infrared radiation and sketched out the shape of our Galaxy; the name of physicist Max Planck (1858-1947) is commemorated in Planck’s constant, a number which lies at the basis of quantum mechanics.

(**) FOCAL (Facility for Optical Calibration At Liège) designates a family of simulators of vacuum environments at the space center of Liège. The number that follows the title indicates the diameter of the simulator enclosure in meters. The FOCAL 5 simulator required the construction (in 1984) of a building for space testing in the Liège Science Park in Sart Tilman.

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