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Planck is in Liège!
5/29/08

A life filled with technological problems and challenges

Planck’s presence at the CSL during the summer season will be noticed. The Center’s priority is conducting the tests on the complete satellite before it is sent into space. The CSL was expecting Planck at the end of 2007, but unexpected difficulties and delays forced it to reschedule its work with the European cosmological observatory.

The FOCAL 5 simulator has been configured to test the satellite in operation at a temperature that is close to absolute zero; the coldest panels measuring minus 269°C! Taking every possible precaution, since the margin for error is extremely small, the CSL teams trained with the help of a mockup to bring Planck’s 1.8 tons into a thermal tent specially constructed for this purpose by the Liège-based company AMOS. The interior of the tent is actually covered with empty beehives attached to copper panels, a process inspired by a similar one employed by the Aerofleet company of Soumagne, Belgium.

details-preparation
The panels were painted black so as to absorb radiant heat flux, and to avoid any heat being reflected from the hot side (electronic) of the satellite, the side of the service module turned toward the sun (the temperature inside this module must remain constant at 20°C), onto the part that has to remain ultra-cold (the telescope and its associated instruments).

Another technological problem that had to be solved: the use of a panel indicating three reference sources that had to come down in front of the HFI instrument assembly and allow it to be calibrated with a heretofore unattained degree of precision. This panel is similar to a liquid helium bath, and was designed to function in a stable manner at temperatures around 4 Kelvin (– 269°C).

Support for the Big Bang theory

In order to keep the core of its payload temperature-controlled under extreme conditions, Planck uses a passive heat sink down to 50 K, and three active cooling units to maintain temperature at 20 K, 4 K, and 100 micro-Kelvin (mK). The latter value for the cooling of the focal plane of the HFI instrument group is achieved by a system of dilution of two isotopes of helium, helium 4 and helium 3. The first occurs naturally, but helium 3 is only produced as a byproduct of nuclear fission, and is one of the most expensive substances in the world (at about 1.2 million euros per kilogram). For Planck alone, the amount used represents two years worth of world production!

The CSL must therefore take every precaution in the testing of the fully operational refrigeration system of the space observatory tested in FOCAL 5.

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