Thermal architecture of the SPICA/SAFARI instrument

The SAFARI instrument is a far infrared imaging spectrometer that is a core instrument of the SPICA mission. Thanks to the large (3 meter) SPICA cold telescope, the ultra sensitive detectors and a powerful Fourier Transform Spectrometer, this instrument will give access to the faintest light never observed in the 34 μm - 210 μm bandwidth with a high spectral resolution. To achieve this goal, TES detectors, that need to be cooled at a temperature as low as 50 mK, have been chosen. The thermal architecture of the SAFARI focal plane unit (FPU) which fulfils the TES detector thermal requirements is presented. In particular, an original 50 mK cooler concept based on a sorption cooler in series with an adiabatic demagnetization refrigerator will be used. The thermal design of the detector focal plane array (FPA) that uses three temperature stages to limit the loads on the lowest temperature stage, will be also described. The current SAFARI thermal budget estimations are presented and discussed regarding the limited SPICA allocations. Finally, preliminary thermal sensitivity analysis dealing with thermal stability requirements is presented.