From now until the month of August, the entire satellite will undergo verification testing and calibration in FOCAL 5. Its core – the telescope and its sensors – will be placed in a vacuum during a sixty-day period, during which it will be exposed to a temperature of 0.1 °K, or 273,05°C. That means it will be in an environment where the temperature is very close to absolute zero! The satellite instrumentation includes two “seeing eyes” that will make observations of the heavens based on nine different wavelengths, in order to measure with unparalleled precision the temperature of the CBR (Cosmic microwave Background Radiation), the “background noise” of the universe. An LFI (Low Frequency Instrument) detector will make observations in the microwave range (30-77 GHz), while the HFI (High Frequency Instrument) package with 36 detectors will measure radiant energy based on infrared radiation from very distant sources, and also emissions in the 100-857 GHz portion of the microwave spectrum. The detectors have to pass qualifying tests so that the CSL can certify that in a vacuum they are sensitive to variations in temperature as small as a few millionths of a degree.

The unavoidable final exam

What is special about Planck, and the thing that makes its preparation so complicated, is that its scientific payload has to function at an ultra-low temperature during a period of 18 months, the time of its space mission. This is the necessary condition for measuring, based on precise observations and with unequaled clarity, the diffuse cosmic background radiation. CSL’s responsibility occurs at a crucial and delicate point of the process: the CSL teams of researchers, engineers and technicians, assisted by specialists from ESTEC and Thales Alenia Space, must give the final “OK” that will allow Planck to join its “buddy” Herschel on a flight to Guiana, soon afterward to be launched into space by an Ariane 5.


This final battery of tests for the Planck satellite is handled with all possible care. Industrial engineer Isabelle Domken has 20 years experience handling space systems testing. She is the director of the CSL team preparing the FOCAL 5 simulator. She is responsible for making sure that the satellite intended to spy out the very origins of the cosmos passes its final exam with flying colors. She reminds us that Planck first visited Liège in 2001, when a feasibility study showed that the CSL had the capacity to test an entire satellite. The facilities had to be adapted for these satellites (construction of an additional wing of the building, expansion of the receiving area), new equipment had to be purchased (helium liquefactor, railway system leading up to the entrance to the simulator enclosure to bring in the satellite, double thermal tent, security arrangements), and engineers had to receive additional training in cryogenic research.