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

N. Mandolesi et al.: The Planck-LFI programmeTable 4. Measured performance parameters of the LFI passivecomponents.Feed HornsOMTsWaveguidesReturn Loss 1 ,Cross-polar(±45 ◦ )andCo-polarpatterns (E, H and ±45 ◦ planes) in amplitudeand phase, Edge taper at 22 ◦Insertion Loss, Return Loss, Cross-polarisation,IsolationInsertion Loss, Return Loss, IsolationNotes. (1) Return loss and patterns (E, H for all frequencies, also ±45 ◦and cross-polar for the 70 GHz system) have been measured for theassembly Feed Horn + OMT as well.Passive components, i.e., feed-horns, OMTs, and waveguides,were tested at room conditions at the Plasma PhysicsInstitute of the National Research Council (IFP-CNR) using aVector Network Analyser. A summary of the measured performanceparameters is provided in Table 4; measurementsand results are discussed in detail in Villa et al. (2009) andD’Arcangelo et al. (2009a,b).In addition, radiometric performance was measured severaltimes during the LFI development on individual subunits(e.g., amplifiers, phase switches, detector diodes) on integratedfront-end and back-end modules (Davis et al. 2009; Artal et al.2009; Varis et al. 2009)andonthecompleteradiometricassemblies,both as independent RCAs (Villa et al. 2010) andinRAA, the final integrated instrument configuration (Mennellaet al. 2010).In Table 5 (taken from Mennella et al. 2010), we list the mainLFI radiometric performance parameters and the integration levelsat which they have been measured. After the flight instrumenttest campaign, the LFI was cryogenically tested again afterintegration on the satellite with the HFI, while the final characterisationwill be performed in-flight before starting nominaloperations.The RCA and RAA test campaigns have been important tocharacterizing the instrument functionality and behaviour, andmeasuring its expected performance in flight conditions. In particular,30 GHz and 44 GHz RCAs were integrated and testedin Italy, at the Thales Alenia Space (TAS-I) laboratories inMilan, while the 70 GHz RCA test campaign was carried out inFinland at the Yilinen-Elektrobit laboratories (Villa et al. 2010).After this testing phase, the 11 RCAs were collected and integratedwith the flight electronics in the LFI main frame atthe TAS-I labs, where the instrument final test and calibrationhas taken place (Mennella et al. 2010). Custom-designed cryofacilities(Terenzi et al. 2009b;Morganteetal.,inprep.)andhigh-performance black-body input loads (Terenzi et al. 2009a;Cuttaia et al. 2009) weredevelopedtotesttheLFIinthemostflight-representative environmental conditions.Aparticularpointmustbemadeaboutthefront-endbiastuning, which is a key step in determining the instrument scientificperformance. Tight mass and power constraints called forasimpledesignoftheDAEboxsothatpowerbiaslinesweredivided into five common-grounded power groups with no biasvoltage readouts. Only the total drain current flowing through thefront-end amplifiers is measured and is available to the housekeepingtelemetry.This design has important implications for front-end biastuning, which depends critically on the satellite electrical andthermal configuration. Therefore, this step was repeated at all integrationstages and will also be repeated during ground satellitetests and in-flight before the start of nominal operations. DetailsTable 5. Main calibration parameters and where they have been/will bemeasured.Category Parameters RCA RAA SAT FLITuning FE LNAs Y Y Y YFE PS Y Y Y YBE offset and gain Y Y Y YQuantisation/compression N Y Y YRadiom. Photometric calibration Y Y Y YLinearity Y Y Y YIsolation Y Y Y YIn-band response Y N N NNoise White noise Y Y Y YKnee freq. Y Y Y Y1/ f slope Y Y Y YSusc. FE temperature fluctuations Y Y Y YBE temperature fluctuations Y Y N NFE bias fluctuations Y Y N NNotes. The following abbreviations have been used: SAT = Satellite;FLI = In-flight; FE = Front-end; BE = Back-end; LNA = Low noiseamplifier; PS = Phase switch; Radiom = Radiometric; and Susc =Susceptibility.Table 6. Calibrated white noise from ground-test results extrapolated tothe CMB input signal level.Frequency channel 30 GHz 44 GHz 70 GHzWhite noise per ν channel 141–154 152–160 130–146[µK· √s]Notes. Two different methods are used to provide a reliable range ofvalues (see Mennella et al. 2010, forfurtherdetails).Thefinalverificationof sensitivity will be derived in-flight during the commissioningperformance verification (CPV) phase.about the bias tuning performed on front-end modules and on theindividual integrated RCAs can be found in Davis et al. (2009),Varis et al. (2009), and Villa et al. (2010).Parameters measured on the integrated instrument werefound to be essentially in line with measurements performedon individual receivers; in particular, the LFI shows excellent1/ f stability and rejection of instrumental systematic effects.On the other hand, the very ambitious sensitivity goals have notbeen fully met and the white noise sensitivity (see Table 6) is∼30% higher than requirements. Nevertheless, the measured performancemakes LFI the most sensitive instrument of its kind, afactor of 2 to 3 superior to WMAP 8 at the same frequencies.6. LFI data processing centre (DPC)To take maximum advantage of the capabilities of the Planckmission and achieve its very ambitious scientific objectives,proper data reduction and scientific analysis procedures were defined,designed, and implemented very carefully. The data processingwas optimized so as to extract the maximum amount ofuseful scientific information from the data set and deliver thecalibrated data to the broad scientific community within a rathershort period of time. As demonstrated by many previous spacemissions using state-of-the-art technologies, optimal scientificexploitation is obtained by combining the robust, well-definedarchitecture of a data pipeline and its associated tools with thehigh scientific creativity essential when facing unpredictable8 Calculated on the final resolution element per unit integration time.Page 15 of 24