Planck Pre-Launch Status Papers - APC - Université Paris Diderot ...

A&A 520, A1 (2010)Fig. 6. The Planck service module consists of a conical mechanical structure around which is supported an octagonal set of panels. It containsall the warm satellite and payload electronic units, with the only exception of the box containing JFETs for impedance-matching to the HFIbolometers (see Fig. 5), which is mounted on the primary reflector support panel, to allow the operation of the JFETs at an optimal temperature of∼130 K . Figure courtesy of Thales Alenia Space (France).values of f k ∼ 20 mHz, i.e. well below the required levelwhich was set taking into account the satellite spin rate,f S ≃ 17 mHz, and the efficiency of destriping algorithms(Maino et al. 2002; Keihänenetal.2005).2. Radiometer thermal fluctuations – The LFI front-end iscooled to 20 K for optimal sensitivity of the indium phosphidecryogenic amplifiers. Fluctuations in the temperatureof the 20 K cold end lead to perturbations of the radiometricdifferential signal through a complex transfer functionwhich depends on the thermal susceptibility of the activeand passive components in the LFI front-end modules andon the damping properties of the instrument thermal mass(Mennella et al. 2010). Stability requirements imposed onthe 20K sorption cooler (see Fig. 8) leadtofluctuationsinthe raw data of