SPIRE Design Description - Research Services

Draft SPIRE Design Description Document
1. INTRODUCTION ....................................................................................................................................6
1.1 The SPIRE instrument and its scientific programme .......................................................................6
1.2 Purpose of this document.................................................................................................................6
1.3 Scope................................................................................................................................................8
2. INSTRUMENT OVERVIEW ..................................................................................................................9
2.1 Photometer design drivers................................................................................................................9
2.2 Spectrometer design drivers.............................................................................................................9
2.3 Instrument functional block diagram .............................................................................................10
2.3.1 Imaging photometer...................................................................................................................12
2.3.2 Fourier transform spectrometer .................................................................................................16
2.3.3 Helium-3 cooler.........................................................................................................................19
3. Instrument System Design ......................................................................................................................20
3.1 SPIRE subsystems..........................................................................................................................20
3.2 The SPIRE instrument as a system ................................................................................................26
3.3 Structural design and FPU integration ...........................................................................................31
3.4 Optical Design................................................................................................................................33
3.4.1 Common optics and photometer optics .....................................................................................33
3.4.2 Spectrometer optical design.......................................................................................................36
3.5 Straylight control............................................................................................................................40
3.5.1 Bandpass filtering ......................................................................................................................40
3.5.2 Baffling......................................................................................................................................41
3.5.3 Diffraction limited optical analysis............................................................................................45
3.5.4 Optical alignment.......................................................................................................................48
3.6 Thermal design...............................................................................................................................48
3.6.1 Instrument temperature levels....................................................................................................48
3.6.2 Cryogenic heat loads..................................................................................................................49
3.6.3 Temperature stability.................................................................................................................50
3.7 EMC...............................................................................................................................................50
3.7.1 Signal quality.............................................................................................................................50
3.7.2 Grounding and RF shield...........................................................................................................50
3.7.3 Microphonics .............................................................................................................................55
3.8 System-level criticality...................................................................................................................55
3.9 Redundancy scheme.......................................................................................................................56
3.10 System budgets ..............................................................................................................................56
4. Subsystem Design...................................................................................................................................57
4.1 Warm Electronics...........................................................................................................................57
4.1.1 Digital Processing Unit (HSDPU) .............................................................................................57
4.1.2 Detector Readout and Control Unit (HSDRCU) .......................................................................61
4.1.3 Detector Control Unit (HSDCU) ...............................................................................................67
4.2 RF Filters........................................................................................................................................69
4.3 JFET units ......................................................................................................................................70
4.4 Bolometric Detector Arrays ...........................................................................................................72
4.4.1 Principle of semiconductor bolometers .....................................................................................72
4.4.2 SPIRE bolometer performance requirements ............................................................................72
4.4.3 SPIRE bolometer design and specifications ..............................................................................73
4.4.4 Bolometer readout electronics ...................................................................................................73
4.4.5 Feedhorns and bolometer cavities..............................................................................................74
4.4.6 Bolometer array thermal-mechanical design .............................................................................76
4.5 Mirrors ...........................................................................................................................................77
4.6 Filters, beam splitters .....................................................................................................................82
4.6.1 Photometer filtering scheme ......................................................................................................82
4.6.2 Spectrometer filtering scheme ...................................................................................................85
4.7 Internal calibrators .........................................................................................................................87
4.7.1 Photometer calibrator (PCAL)...................................................................................................87
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