Thermal Design and Thermal Behaviour of Radio Telescopes and their Enclosures Bearbeitet von Albert Greve, Michael Bremer 1. Auflage 2010. Buch. X, 420 S. Hardcover ISBN 978 3 642 03866 2 Format (B x L): 15,5 x 23,5 cm Gewicht: 795 g Weitere Fachgebiete > Physik, Astronomie > Astronomie: Allgemeines > Astronomische Beobachtung: Observatorien, Instrumente, Methoden Zu Leseprobe schnell und portofrei erhältlich bei Die Online-Fachbuchhandlung beck-shop.de ist spezialisiert auf Fachbücher, insbesondere Recht, Steuern und Wirtschaft. Im Sortiment finden Sie alle Medien (Bücher, Zeitschriften, CDs, ebooks, etc.) aller Verlage. Ergänzt wird das Programm durch Services wie Neuerscheinungsdienst oder Zusammenstellungen von Büchern zu Sonderpreisen. Der Shop führt mehr als 8 Millionen Produkte.
1 Radio Astronomy and Radio Telescopes... 1 1.1 Radio Wavelengths and Radio Telescopes... 1 1.2 Deep Space Network and Large Communication Antennas... 9 1.3 Radio Telescopes in Space... 10 1.4 Overview of Telescope Constructions... 10 2 Radio Telescope Constructions in View of Thermal Aspects... 13 2.1 Optical Configurations... 14 2.1.1 The Parabolic Reflector... 14 2.1.2 The Cassegrain and Gregory System... 15 2.2 Basic Telescope Constructions... 19 2.2.1 The Telescope with Alidade Support... 20 2.2.2 The Telescope with Pedestal Yoke Support... 22 2.2.3 The Telescope with Pedestal Fork Support... 25 2.3 Telescope Components... 29 2.3.1 Reflector Backup Structure (BUS)... 29 2.3.2 The Homologous BUS... 34 2.3.3 The Open and Closed, Ventilated and Climatised BUS... 35 2.3.4 Reflector Panels... 38 2.3.5 Active Reflector Surface... 42 2.3.6 The Quadripod and Subreflector... 43 2.3.7 The Secondary Focus Cabin... 43 2.4 The Thermal Design of Radio Telescopes... 44 3 Telescope Enclosures... 49 4 The Variable Thermal Environment... 55 4.1 The Environment and Observatory Sites... 55 4.2 The Ambient Air... 57 4.3 The Ambient Air Temperature... 59 4.3.1 Measured Ambient Air Temperatures... 59 xvii
xviii 4.3.2 Approximation of the Daily Ambient Air Temperature... 62 4.3.3 Rate of Ambient Air Temperature Change... 64 4.4 Wind Speed and Wind Direction... 65 4.4.1 Measured Wind Speeds... 65 4.4.2 Wind Speed and Convective Heat Transfer... 68 4.5 Ground Temperature... 69 4.5.1 Measured Ground Temperatures... 69 4.5.2 Approximation of the Ground Temperature... 70 4.6 Humidity, Condensation, Icing... 71 4.6.1 Humidity and Sky Radiation... 73 4.7 Sky Temperature... 74 4.7.1 Measured Sky Temperature... 75 4.7.2 Calculation of the Sky Temperature... 75 4.8 Cloud Coverage... 79 4.9 Solar Radiation... 79 4.9.1 Measurements of Solar Radiation... 81 4.10 Meteorological Design Specifications... 82 4.11 Space Environment... 83 5 Calculation of Solar Illumination... 85 5.1 The Apparent Motion of the Sun... 85 5.2 The Plane Surface... 88 5.3 The Tube Surface... 91 5.4 The Parabolic Reflector Surface... 92 5.4.1 Borderline between Shadow and Sunshine... 92 5.4.2 Solar Illumination of the Reflector Surface... 94 5.5 The Open and Closed BUS... 96 5.6 The Box type Enclosure (Astrodome)... 97 5.7 The Cylindrical Enclosure (Astrodome)... 98 5.8 The Over Hemispherical Radome... 99 5.9 Manipulation of Insolation through Surface Finish...102 5.10 Sun on Subreflector and Quadripod...104 6 Temperature Measurements and FEM Thermal Deformation Calculations...107 6.1 Electric Resistance Temperature Sensors...108 6.2 Temperature Measurements by Infrared Radiation...110 6.3 Temperature Sampling Rate...110 6.4 Location of Temperature Sensors (InterpolationMatrixandInfluenceMatrix)...111 6.5 Precision of Temperature Measurements...118 6.6 Prediction of Temperature induced Deformations...118 6.7 Empirical Relations...120 6.8 Temperature related Measurements...120
xix 7 Heat Transfer...123 7.1 Laws of Thermodynamics and Modes of Heat Transfer...123 7.2 Amount of Heat transferred...124 7.3 Heat Content...126 7.4 Heat Transfer by Conduction...127 7.5 Heat Transfer by Convection...130 7.6 Heat Transfer by Conduction and Convection...132 7.7 The Convective Heat Transfer Coefficient (h)...133 7.7.1 Forced Convection...134 7.7.2 Natural Convection...138 7.7.3 Forced Convection and Ventilation...139 7.7.4 Natural Convection and Ventilation...140 7.8 Radiative Heat Transfer...141 7.9 Heat Transfer by Conduction, Convection and Radiation...145 7.10 Radiative Nodes and View Factors...146 7.10.1 Radiative Nodes...146 7.10.2 View Factor Relations...148 7.10.3 Internal View Factors...149 7.11 Energy/Heat Conservation...152 7.12 The Steady and Non Steady Thermal State...155 7.12.1 External Thermal Time Constant τ ext...155 7.12.2 Internal Thermal Time Constant τ int (Conduction)...159 8 Radiative Coupling towards Sky and Ground (External View Factor)...161 8.1 Vertical and Horizontal Walls...163 8.2 The Radome and Astrodome...165 8.3 The Parabolic Reflector...166 8.4 The Open and Closed BUS...170 9 Measured Thermal Behaviour of Radio Telescopes...173 9.1 Telescope Supports...174 9.1.1 The Pedestal...174 9.1.2 The Alidade...178 9.1.3 The Fork Support...186 9.1.4 Path Length Variations of Telescope Supports (forradiointerferometerandvlbiarrays)...192 9.2 BUS Supports...196 9.2.1 The (climatised) Yoke...197 9.2.2 The Central Hub...199 9.3 Backup Structures (BUS)...203 9.3.1 The Open BUS...206 9.3.2 The Closed BUS...209 9.3.3 The Ventilated BUS...216 9.3.4 Radial and Circular Ventilation...220
xx 9.3.5 The Climatised BUS (IRAM 30 m Telescope)...222 9.3.6 Thermal Deformations and Active Reflector Surfaces...225 9.3.7 The Radome/Astrodome enclosed BUS...226 9.3.8 Temperature Changes of the BUS and Focus Changes...231 9.4 Panels...232 9.4.1 Experimental Data of Panel Temperatures...233 9.4.2 Panel Temperatures measured on Telescopes...234 9.4.3 Thermal Panel Buckling...234 9.4.4 Heated Panels, De icing of Panels...239 9.5 Quadripod, Subreflector, Focus Cabins...242 9.5.1 Quadripod...242 9.5.2 Subreflector...246 9.5.3 Focus Cabins...247 9.6 Observations in the Direction of the Sun...248 9.7 De icing of a Telescope...250 9.8 Measured Temperature Uniformity of Radio Telescopes...251 9.9 The measured Thermal Behaviour of Telescopes...255 9.10 Temperature Monitoring and Trouble Shooting...258 9.11 Other Thermal Effects...261 10 Measured Thermal Behaviour of Enclosures...263 11 Thermal Model Calculations...267 11.1 Mechanical Models of Structural Components...268 11.2 Static Thermal Calculations (TheUseofKnownTemperatureDistributions)...271 11.3 Dynamic Thermal Model Calculations (TheDerivationofTemperatureDistributions)...271 11.4 Node Structure of Thermal Models...273 11.5 The Thermal Environment as Input Data...274 11.6 Models of Panels...275 11.7 Model of Telescope Supports...279 11.7.1 Model of an Alidade...279 11.7.2 Model of a Yoke...281 11.7.3 Model of a Fork Support...282 11.8 Model of a Backup Structure...288 11.8.1 Model of an Open BUS...289 11.8.2 Model of a Closed BUS with Natural Ventilation...290 11.8.3 Model of a Closed BUS with Forced Ventilation...291 11.9 Model of a Radome and Closed Astrodome...297 11.10 Servo loop Controlled Ventilation/Heating/Cooling...299 11.11 Model Calculations and Energy Balance...300 11.12 Model Calculations for Operational Purposes...302 11.13 Precision of Model Calculations...303 11.14 Programmes for Model Calculations...304
xxi 12 Beam Formation and Beam Degradation...305 12.1 Wave Propagation and Beam Formation...305 12.2 The Perfect Radio Telescope...308 12.3 The Beam Pattern of the Perfect Radio Telescope...311 12.4 The Real Radio Telescope...313 12.4.1 Systematic Wavefront Deformations...313 12.4.2 Repetitive Wavefront Deformations (ThermalPanelBuckling)...316 12.4.3 Random Wavefront Deformations...318 12.5 Superposition of Random and Systematic (Thermal) Deformations321 12.6 Beam Deformations and Thermal Tolerances...322 13 Thermal Tolerances...325 13.1 Global Estimates of Temperature Influences...326 13.1.1 Reflector Diameter Estimates...327 13.1.2 Estimated Thermal Behaviour of a BUS...328 13.1.3 Estimated Thermal Behaviour of an Alidade/Fork Support 330 13.1.4 Estimated Thermal Behaviour of Panels...331 13.2 System Alignment Tolerances...331 13.2.1 Displacements and Tilts of Main Reflector and Subreflector...331 13.2.2 Temperature induced Pointing Errors...335 13.2.3 Alignment Errors: Temperature Tolerance Estimates...336 13.3 Random Reflector Errors...337 13.4 Design Specifications and Error Budget...340 14 Optical Telescopes and Enclosures...343 15 A Summary and Further Studies...347 15.1 A Summary of the Present State...347 15.2 Temperature Measurements and Dynamic Thermal Models...348 15.3 Further Studies...349 15.4 A Dynamic Thermal Error Budget for Design...352 15.5 A Fundamental Investigation of Radio Telescope/Antenna Constructions...353 15.6 Future Design...355 A Units and Fundamental Constants...357 B Average Value, Root Mean Square Value (rms)...361 C Pointing Model...363 D Zernike Polynomials...367 Picture and Graphic Credits...369
xxii References...373 Indices...383 Historical Names Index...384 Author Index...385 Book Index...388 Subject Index...389