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M. Bersanelli et al.: Planck pre-launch status: Design and description of the Low Frequency Instrumentscanning strategy, a higher knee frequency ( f k < 50 mHz) is acceptableas robust destriping and map making algorithms canbe successfully applied to suppress the effects of low-frequencyfluctuations. Because a total power HEMT receiver would havetypical knee frequencies of 10 to 100 Hz, a very efficient differentialdesign is needed for LFI to meet the 50 mHz requirement.2.5. Systematic effectsThroughout the design and development of LFI a key driverhas been the minimisation and control of systematic effects,i.e., deviations from the signal that would be produced by aninstrument with axially symmetric Gaussian beams, with idealpointing and pure Gaussian white noise. These include opticaleffects (e.g., straylight, misalignment, beam distortions), instrumentintrinsic effects (e.g., non-stationary and correlated noisefeatures such as 1/ f noise, spikes, glitches, etc.), thermal effects(e.g., temperature fluctuations in the front-end or otherinstrument interfaces), and pointing errors. In particular, theLFI receiver (discussed in Sect. 3) wasdesignedwiththeprimaryobjective of minimising the impact of 1/ f noise, thermalfluctuations, and systematic effects due to non-ideal receivercomponents.The quantitative evaluation of various potential systematiceffects required a complex iterative process involving designchoices, knowledge and stability of the interfaces (with HFI andwith the satellite), testing and modelling of the instrument behaviour,and simulations and simplified data analysis to evaluatethe impact of each effect on the scientific output of the mission(Mennella et al. 2004). Furthermore, dedicated analyses wererequired to evaluate the impact of instrument non-idealities onpolarisation measurements (Leahy et al. 2010).Limits on systematic effects impacting the effective angularresolution (beam ellipticity, alignment, pointing errors) wereused, together with those coming from HFI, as input to the designof the Planck telescope and focal plane, as well as to setpointing requirements at the system level. Regarding signal perturbations,for LFI we set an upper limit to the global impactof systematic effects of
A&A 520, A4 (2010)Fig. 2. Schematic of the LFI system displaying the main thermal interfaceswith the V-grooves and connections with the 20 K and 4 K coolers.Two RCAs only are shown in this scheme. The radiometer arrayassembly (RAA) is represented by the shaded area and comprises thefront-end unit (FEU) and back-end unit (BEU). The entire LFI RAAincludes 11 RCAs, with 11 feeds, 22 radiometers, and 44 detectors.Fig. 1. Top: schematicofaradiometerchainassembly(RCA).TheLFI array has 11 RCAs, each comprising two radiometers carrying thetwo orthogonal polarisations. The RCA is constituted by a feed horn,an orthomode transducer (OMT), a front-end module (FEM) operatedat 20 K, a set of four waveguides that connect FEM to the back-endmodule (BEM). The notations “0” and “1” for the two radiometers inthe RCA denote the branches downstream of the main and side armsof the OMT, respectively. Each amplifier chain assembly (ACA) comprisesa cascaded amplifier and a phase switch. Bottom: pictureofa30 GHz RCA integrated before radiometer-level tests.3.2. Radiometer array assemblyAschematicoftheradiometerarrayassembly(RAA),isshownin Fig. 2. EachRCAhasbeenintegratedandtestedseparately,and then mounted on the RAA without de-integration to ensurestability of the radiometer characteristics after calibrationat RCA level (Villa et al. 2010).A“mainframe”supportstheLFI20Kfrontend(withfeeds,OMTs, and FEMs) and interfaces the HFI 4 K front-end box inthe central portion of the focal plane. The HFI 4 K box is linkedto the 20 K LFI mainframe with insulating struts and providesthe thermal and mechanical interface to the LFI reference loads.Forty-four waveguides connect the LFI front-end unit (FEU) tothe back-end unit (BEU), which is mounted on the top panel ofthe Planck service module (SVM) and is maintained at a temperatureof ∼300 K. The BEU comprises the eleven BEMs andthe data acquisition electronics (DAE) unit. After on-board processing,provided by the radiometer box electronics assembly(REBA), the compressed signal is down-linked to the groundstation with housekeeping data.Amajordesigndriverhasbeentoensureacceptablylowconductive and radiative parasitic thermal loads at the 20 Kstage, particularly those introduced by the waveguides and cryoharness.As we discuss below, sophisticated design solutionswere implemented for these units. In addition, three thermalsinks were used to largely reduce the parasitic loads in the 20 Kstage, and these are the three conical shields (V-grooves) introducedin the Planck payload module to thermally isolate thecold telescope enclosure from the SVM at ∼300 K (Tauber et al.2010a). The V-grooves also provide multiple precool temperaturesto all of the Planck coolers, as well as intercepting parasiticsfrom the cooler piping and HFI equipment. The threeV-grooves are expected to reach in-flight temperatures of approximately170 K, 100 K, and 50 K.The FEU is aligned in the focal plane of the telescope andsupported by a set of three thermally insulating bipods attachedto the telescope structure. The back-end unit is fixed on top of thePlanck service module, below the lower V-groove. In Fig. 3 weshow a detailed drawing of the RAA, including an exploded viewshowing its main subassemblies and units. After integration, theRAA was first tested in a dedicated cryo-facility (Mennella et al.2010) forinstrumentleveltests(Fig.4), and then inserted intoPage 6 of 21
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A&A 520, E1 (2010)DOI: 10.1051/0004
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ABSTRACTThe European Space Agency
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A&A 520, A1 (2010)Fig. 2. An artist
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A&A 520, A1 (2010)Fig. 4. Planck fo
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A&A 520, A1 (2010)Fig. 6. The Planc
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A&A 520, A1 (2010)Table 4. Summary
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A&A 520, A1 (2010)three frequency c
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A&A 520, A1 (2010)Fig. 12. The left
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A&A 520, A1 (2010)Fig. 14. Left pan
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A&A 520, A1 (2010)flux limit of the
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A&A 520, A1 (2010)- University of C
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Page 61 and 62: A&A 520, A3 (2010)features of the r
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A&A 520, A7 (2010)Fig. 8. Footprint
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-30-40-30-6-3-20A&A 520, A7 (2010)0
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A&A 520, A7 (2010)Table 4. Galactic
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A&A 520, A7 (2010)Fig. A.1. Polariz
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A&A 520, A8 (2010)inflation, giving
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A&A 520, A8 (2010)estimated from th
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A&A 520, A8 (2010)ways the most str
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unmodelled long-timescale thermally
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A&A 520, A8 (2010)Fig. 5. Polarisat
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A&A 520, A8 (2010)Table 3. Band-ave
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A&A 520, A8 (2010)where S stands fo
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A&A 520, A8 (2010)Fig. 11. Simulate
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stored in the LFI instrument model,
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A&A 520, A8 (2010)Table 5. Statisti
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A&A 520, A8 (2010)comparable in siz
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A&A 520, A8 (2010)Table B.1. Main b
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A&A 520, A8 (2010)Bond, J. R., Jaff
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A&A 520, A9 (2010)- (v) an optical
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A&A 520, A9 (2010)Fig. 2. The Russi
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A&A 520, A9 (2010)Table 3. Estimate
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A&A 520, A9 (2010)Fig. 7. Picture o
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A&A 520, A9 (2010)Fig. 9. Cosmic ra
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A&A 520, A9 (2010)Fig. 13. Principl
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A&A 520, A9 (2010)Fig. 16. Noise sp
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A&A 520, A9 (2010)Table 6. Basic ch
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A&A 520, A9 (2010)with warm preampl
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A&A 520, A9 (2010)20 Laboratoire de
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A&A 520, A10 (2010)Table 1. HFI des
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A&A 520, A10 (2010)based on the the
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A&A 520, A10 (2010)Fig. 6. The Satu
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A&A 520, A10 (2010)5. Calibration a
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A&A 520, A10 (2010)Fig. 16. Couplin
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A&A 520, A10 (2010)217-5a channel:
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A&A 520, A10 (2010)10 -310 -495-The
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P. A. R. Ade et al.: Planck pre-lau
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A&A 520, A12 (2010)Table 1. Summary
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arrangement was also constrained by
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A&A 520, A12 (2010)frequency cut-of
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A&A 520, A12 (2010)Fig. 9. Gaussian
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A&A 520, A12 (2010)the horn-to-horn
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A&A 520, A12 (2010)Fig. 19. Broad-b
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C. Rosset et al.: Planck-HFI: polar
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of frequencies and shown to have po
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