PLANCK HIGH FREQUENCY INSTRUMENT - DESIGN AND TESTING OF THEHFI 0,1K COOLER STRUCTURES, WITH A SHAPE MEORY ALLOYLAUNCH BLOCKING SYSTEM

摘要

Planck is the European infra-red space observatory thatwill map the temperature anisotropies of the cosmicbackground radiation. The space-borne telescope willfocus the infrared light onto the Low FrequencyInstrument, LFI (30 GHz to 100 GHz) and the HighFrequency Instrument, HFI (100 GHz to 857 GHz).AIR LIQUIDE and the CNRS/CRTBT, are in charge ofthe design, manufacturing and qualification, of the HFIstructure and its 0,1K helium dilution cooler, under theprime contractorship of IAS, the Principal Investigatorof HFI, and financed by CNES, the French NationalSpace Agency.The 0,1K functional temperature requirement of theinstrument, produced and maintained by the 100nWpower of the Helium Dilution Cooler, can only beachieved with a thermally optimized architecture, withminimal conductive heat entries, and very thin structuralelements that are not compatible with the mechanicalloads experienced during launch. In order to fulfill theseconflicting requirements, AIR LIQUIDE has developeda specific launch blocking system, based on a shapememory alloy technique, that provides a high stiffnessand mechanical strength during the launch phase, and acomplete thermal and mechanical decoupling once inorbit. This passive system, composed of a clamp and ashape memory alloy mechanism, opens and closesautomatically at a determined temperature, without anyelectrical power. This rigid clamp provides a 2500Ntightening force to restrain the core of the HFIinstrument, and help it to withstand the Ariane-5 launchenvironment.After the launch, the clamp is cooled by conductionthrough the spacecraft to its opening temperature at200K, and the key elements of HFI and 0,1K Cooler arereleased. Once the clamp opened, the center part of HFIis freed from any significant heat entry, and the dilutioncooler can bring the instrument sensors down to the0.1K necessary for the deep space observation.In order to implement such a mechanism, a specificshape memory alloy has been developed incollaboration with the suppliers, to achieve the targetopening temperature and material elongation.The HFI mechanical test campaign, conducted by AIRLIQUIDE, has qualified the hardware to the Ariane-5launch loads, and has demonstrated the efficiency of thelaunch blocking mechanism up to 40g's.