Planck Pre-Launch Status Papers - APC - UniversitÃ© Paris Diderot ...

More documents

Recommendations

Info

J. A. Tauber et al.: Planck pre-launch status: The optical systemTable 1. Design requirements of the Planck telescope reflectors.Fig. 2. The layout of the focal plane of Planck.TheLFIhornssurroundthe HFI focal plane (circular structure in the centre of the figure). Seealso Fig. 4.the reflectors (conic constants and radius of curvature) and telescope(distances and angles between reflectors and focal plane).The merit function was the minimisation of the quadratic sumof the wavefront error (WFE) at 16 points in the focal planefield (8 for LFI and 8 for HFI). After each optimisation run,the radiation patterns were computed using physical optics withthe GRASP software and the horn tapers were readjusted tokeep spillover power within allowed straylight levels. Care wasalso taken to maintain minimum mechanical distances betweenhorns, and to reduce obscuration and mutual electromagnetic effects.The resulting optimised telescope is an aplanatic one consistingof two ellipsoidal reflectors, and is described in Sect. 3and Appendix A.Once the intended optical prescription was established, highlevel requirements for hardware production were set mainly interms of WFE, but also in terms of peak gain degradation, ellipticity,and straylight levels. The maximum WFE levels requiredfor each detector were calculated (based on ideal feedhorns withspecified taper levels and the optimised telescope design prescription),and we constrained themostaccuratepre-launchestimateof the in-flight WFE to be lower than that level within aspecified tolerance. The surface characteristics of the reflectorsdetermine to a significant degree the total WFE of the system,and during their manufacture a specific set of mechanical requirements(Table 1) was imposed from a sub-allocation of themaximum WFEs. All the requirements, whether at system or reflectorlevel, were required to be met at operational temperature.3. Mechanical configuration and manufactureThe major elements constituent of the optical system of Planckare considered to be the following (see Fig. 3):– The detector feedhorns, designed, manufactured and testedby the LFI and HFI instrument teams (Villa et al. 2010,in prep.; Sandri et al. 2010; Maffei et al. 2010).– The Planck telescope, consisting of:– the primary and secondary reflectors (PR and SR), designedand manufactured by Astrium (Friedrichshafen,Germany);– the support structure, designed and manufactured byOerlikon Space (Zürich, Switzerland).– The baffle 2 surrounding the telescope, designed and manufacturedby Contraves (Zürich, Switzerland).2 The baffle isusedforstraylightcontrol,butalsohasanimportantthermal function, increasing substantially the capacity to radiate passivelyto cold space.Requirement Primary reflector Secondary reflectorContour shape off-axis ellipsoid off-axis ellipsoidSize (mm) 1555.98 × 1886.79 1050.96 × 1104.39Radius ofCurvature (mm) 1440 ± 0.25 −643.972 ± 0.2Conic constant −0.86940 ± 0.0003 −0.215424 ± 0.0003Stability of best fit ellipsoidalong each axis±0.1 mmaround each axis±0.1 mradMechanical surface errors rms spec (goal) aring 17.5 µm (5µm)ring 212 µm (8µm)ring 320 µm (13µm)ring 433 µm (22µm)ring 550 µm (33µm)Surface roughness R q < 0.2 µm onscales99.5 per centEnd of life>98.5 (goal 99.0) cMass 30.6 kg 14.5 kgFirst eigenfrequency>120 HzTemperaturesOperational45 KQualification30−325 KNotes. (a) Each ring is a concentric ellipse with the same ellipticity asthe rim of the reflector, dividing the major axis in 5 equal pieces. Ring 1is the innermost ring and ring 6 the outermost one.(b) Defined in Sect. 3.1.(c)At telescope level, the total emissivity is specified to be
A&A 520, A2 (2010)Fig. 3. (Top)Twosideviewsofthepayloadmodule,showingmainlythethree V-grooves, which radiatively insulate the payload from the warmpart of the satellite, and the large baffle usedforstraylightcontrolandradiative cooling. (Bottom) Across-sectionalsketchoftheoptimisedPlanck telescope design, showing the reflectors support structure andthe focal plane. The principal (right-handed) coordinate systems are indicated.The rotation of the spin axis is about the +X TEL direction.3.2. Design and manufacture of the reflectorsThe strong requirement imposed on the Planck reflectors to minimizedeformations between room temperature and operationalconditions (∼40 K) led to the selection of carbon fiber reinforcedplastic (CFRP) honeycomb sandwich technology, in which acarefully controlled mixture of carbon fibers and resin yields aneffective thermal expansion coefficient, which is close to zero inthe temperature range relevant to Planck.The main parameters driving the CFRP design are the size,mass, maximum reflector thickness and lowest eigenfrequency.Furthermore, because of the differences in mechanical propertiesof the CFRP and the adhesion between the front facesheetand the core, the CFRP membrane within each core cell hasatendencytobecomeslightlyconcave(thiseffect is usuallycalled “dimpling”). Although the effect is small, it was expectedbased on a Finite Element Model to be systematically presentin all core cells, and therefore to enhance the response of thetelescope in specific narrow areas on the sky, away from themain beam (“grating lobes”). To decrease the dimpling effect,athickerfacesheetwasrequired,whichalsoincreasedthefirsteigenfrequency. The final design of the reflector sandwich structurewas based on detailed simulations exploiting the full availablevolume and minimizing the dimpling effect and the mass.This resulted in the selection of hexagonal core cells with a pitchof 60 mm and a wall thickness of 0.8 mm; the final thickness ofthe facesheets in the center of the reflectors is 2.178 mm.Amoredetaileddiscussionofthemechanicaldesignandmanufacturing of the Planck reflectors can be found in Stute(2005).The Planck reflectors were produced by Astrium, Germany(ASED), under contract to ESA and the Danish National SpaceInstitute (DTU-Space). The facesheets were made by layingcarbon fibers on high-precision, cast-steel, optically polishedmoulds. ASED developed a numerically-controlled fiber placementtechnology, where the fibers are impregnated during thelay-up process with a precise amount of resin. To assure homogeneity,layers with the fiber direction at different angles werecombined to form a laminate. In the case of the Planck reflectors,the facesheets were doubly curved. To assure a true-anglelay-up over the whole reflector, ASED developed a special algorithmfor their lay-up machine. The facesheet fibers were laid upin 4 + 4symmetricallayers(0 ◦ ,45 ◦ , −45 ◦ ,90 ◦ ). The fibers usedfor the top and bottom layers were selected especially to preventcracks on the surfaces of the facesheets. Once the fiber material,the resin, and the details of the lay-up are selected, the main parametergoverning the mechanical properties of the laminate isthe fiber volume content. For Planck, thefibervolumecontentwas 60%, and a resin with low curing temperature was selected,to minimize the build-up of internal stresses.The cores for the inner honeycomb were produced by filamentwinding of hexagon-shaped mandrels, a fiber volumecontent being chosen so that the CTE matched the CTE ofthe facesheets. The honeycomb cells were glued together andthe composite milled into the correct shape and size. Finally,the front facesheet, the core structure, and the back facesheetwere glued together using the mould again as support.The primary and secondary reflectors were manufactured inthe same way, the only difference being their size and shape.To fulfill the reflectivity requirement, the reflectors werecoated with 0.5 µm vacuum-depositedaluminium.Toassuregood adhesion, first a NiCr layer, then the aluminium layer, andon top a hard protection layer of Plasil (SiO x )weredeposited.The coating was performed at the Balzer coating facility in theCalar Alto Observatory in Spain. Measurements of the emissivityare described in Appendix B.3.3. The structure and baffleThe 2 Planck reflectors are supported by a CFRP structure ofsquare tubes. The interface between the reflectors and the telescopestructure consists of 3 so-called isostatic mounts (ISMs).The ISM’s are weak in the radial but stiff in the tangential direction.This design assures that deformation of the telescopestructure does not affect the reflectors. The ISMs are madeof titanium.The baffle surrounding the telescope is made from aluminiumhoneycomb, which is open on the outside to maximisethe radiating surface. To minimize the background radiation insidethe baffle cavity,thesurfacesofthetelescopestructurearecovered by aluminized kapton foil, while the inside of the baffleis coated with pure aluminium. Outside the cavity, the surfacesare coated with high emissivity paint to improve radiativecooling.Page 4 of 22
Page 1 and 2: A&A 520, E1 (2010)DOI: 10.1051/0004
Page 3 and 4: ABSTRACTThe European Space Agency
Page 5 and 6: A&A 520, A1 (2010)Fig. 2. An artist
Page 7 and 8: A&A 520, A1 (2010)Fig. 4. Planck fo
Page 9 and 10: A&A 520, A1 (2010)Fig. 6. The Planc
Page 11 and 12: A&A 520, A1 (2010)Table 4. Summary
Page 13 and 14: A&A 520, A1 (2010)three frequency c
Page 15 and 16: A&A 520, A1 (2010)Fig. 12. The left
Page 17 and 18: A&A 520, A1 (2010)Fig. 14. Left pan
Page 19 and 20: A&A 520, A1 (2010)flux limit of the
Page 21 and 22: A&A 520, A1 (2010)- University of C
Page 23 and 24: A&A 520, A1 (2010)57 Instituto de A
Page 25: A&A 520, A2 (2010)Fig. 1. (Left) Th
Page 29 and 30: A&A 520, A2 (2010)Table 2. Predicte
Page 31 and 32: Table 3. Predicted in-flight main b
Page 33 and 34: A&A 520, A2 (2010)materials. Theref
Page 35 and 36: A&A 520, A2 (2010)Fig. 11. Comparis
Page 37 and 38: A&A 520, A2 (2010)Table 5. Inputs u
Page 39 and 40: A&A 520, A2 (2010)Fig. 16. Three cu
Page 41 and 42: A&A 520, A2 (2010)Table 7. Optical
Page 43 and 44: A&A 520, A2 (2010)Fig. A.1. Dimensi
Page 45 and 46: A&A 520, A2 (2010)5 Università deg
Page 47 and 48: A&A 520, A3 (2010)Horizon 2000 medi
Page 49 and 50: A&A 520, A3 (2010)Fig. 1. CMB tempe
Page 51 and 52: A&A 520, A3 (2010)Ω ch 2τn s0.130
Page 53 and 54: A&A 520, A3 (2010)Fig. 6. Integral
Page 55 and 56: A&A 520, A3 (2010)Table 2. LFI opti
Page 57 and 58: 3.3.1. SpecificationsThe main requi
Page 59 and 60: A&A 520, A3 (2010)Fig. 11. Schemati
Page 61 and 62: A&A 520, A3 (2010)features of the r
Page 63 and 64: A&A 520, A3 (2010)Fig. 13. Level 2
Page 65 and 66: A&A 520, A3 (2010)Fig. 15. Level 3
Page 67 and 68: A&A 520, A3 (2010)GUI = graphical u
Page 69 and 70: A&A 520, A3 (2010)23 Centre of Math
Page 71 and 72: A&A 520, A4 (2010)In addition, all
Page 73 and 74: A&A 520, A4 (2010)Table 2. Sensitiv
Page 75 and 76: A&A 520, A4 (2010)Fig. 2. Schematic
Page 77 and 78:
A&A 520, A4 (2010)Fig. 6. LFI recei
Page 79 and 80:
A&A 520, A4 (2010)Fig. 9. Schematic
Page 81 and 82:
A&A 520, A4 (2010)Table 4. Specific
Page 83 and 84:
A&A 520, A4 (2010)Fig. 15. DAE bias
Page 85 and 86:
A&A 520, A4 (2010)Fig. 19. Picture
Page 87 and 88:
A&A 520, A4 (2010)Table 10. Main ch
Page 89 and 90:
Table 13. Principal requirements an
Page 91 and 92:
A&A 520, A5 (2010)DOI: 10.1051/0004
Page 93 and 94:
A. Mennella et al.: LFI calibration
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
D.1. Step 1-extrapolate uncalibrate
Page 107 and 108:
A&A 520, A6 (2010)DOI: 10.1051/0004
Page 109 and 110:
F. Villa et al.: Calibration of LFI
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
A&A 520, A7 (2010)DOI: 10.1051/0004
Page 123 and 124:
M. Sandri et al.: Planck pre-launch
Page 126 and 127:
A&A 520, A7 (2010)Fig. 8. Footprint
Page 128 and 129:
-30-40-30-6-3-20A&A 520, A7 (2010)0
Page 130 and 131:
A&A 520, A7 (2010)Table 4. Galactic
Page 132 and 133:
A&A 520, A7 (2010)Fig. A.1. Polariz
Page 134 and 135:
A&A 520, A8 (2010)inflation, giving
Page 136 and 137:
A&A 520, A8 (2010)estimated from th
Page 138 and 139:
A&A 520, A8 (2010)ways the most str
Page 140 and 141:
unmodelled long-timescale thermally
Page 142 and 143:
A&A 520, A8 (2010)Fig. 5. Polarisat
Page 144 and 145:
A&A 520, A8 (2010)Table 3. Band-ave
Page 146 and 147:
A&A 520, A8 (2010)where S stands fo
Page 148 and 149:
A&A 520, A8 (2010)Fig. 11. Simulate
Page 150 and 151:
stored in the LFI instrument model,
Page 152 and 153:
A&A 520, A8 (2010)Table 5. Statisti
Page 154 and 155:
A&A 520, A8 (2010)comparable in siz
Page 156 and 157:
A&A 520, A8 (2010)Table B.1. Main b
Page 158 and 159:
A&A 520, A8 (2010)Bond, J. R., Jaff
Page 160 and 161:
A&A 520, A9 (2010)- (v) an optical
Page 162 and 163:
A&A 520, A9 (2010)Fig. 2. The Russi
Page 164 and 165:
A&A 520, A9 (2010)Table 3. Estimate
Page 166 and 167:
A&A 520, A9 (2010)Fig. 7. Picture o
Page 168 and 169:
A&A 520, A9 (2010)Fig. 9. Cosmic ra
Page 170 and 171:
A&A 520, A9 (2010)Fig. 13. Principl
Page 172 and 173:
A&A 520, A9 (2010)Fig. 16. Noise sp
Page 174 and 175:
A&A 520, A9 (2010)Table 6. Basic ch
Page 176 and 177:
A&A 520, A9 (2010)with warm preampl
Page 178 and 179:
A&A 520, A9 (2010)20 Laboratoire de
Page 180 and 181:
A&A 520, A10 (2010)Table 1. HFI des
Page 182 and 183:
A&A 520, A10 (2010)based on the the
Page 184 and 185:
A&A 520, A10 (2010)Fig. 6. The Satu
Page 186 and 187:
A&A 520, A10 (2010)5. Calibration a
Page 188 and 189:
A&A 520, A10 (2010)Fig. 16. Couplin
Page 190 and 191:
A&A 520, A10 (2010)217-5a channel:
Page 192 and 193:
A&A 520, A10 (2010)10 -310 -495-The
Page 194 and 195:
A&A 520, A11 (2010)DOI: 10.1051/000
Page 196 and 197:
P. A. R. Ade et al.: Planck pre-lau
Page 198 and 199:
Page 200 and 201:
Page 202 and 203:
A&A 520, A12 (2010)Table 1. Summary
Page 204 and 205:
arrangement was also constrained by
Page 206 and 207:
A&A 520, A12 (2010)frequency cut-of
Page 208 and 209:
A&A 520, A12 (2010)Fig. 9. Gaussian
Page 210 and 211:
A&A 520, A12 (2010)the horn-to-horn
Page 212 and 213:
A&A 520, A12 (2010)Fig. 15. Composi
Page 214 and 215:
A&A 520, A12 (2010)Fig. 19. Broad-b
Page 216 and 217:
A&A 520, A13 (2010)DOI: 10.1051/000
Page 218 and 219:
C. Rosset et al.: Planck-HFI: polar
Page 220 and 221:
Page 222 and 223:
of frequencies and shown to have po
Page 224 and 225:
Page 226 and 227:
show all

Planck Pre-Launch Status Papers - APC - UniversitÃ© Paris Diderot ...

Create successful ePaper yourself

Delete template?

Save as template?