Thermal Design and Thermal Behavior of Radio Telescopes [PDF]

*********************************************************************************** ~~~Thermal Design and Thermal Behavior of Radio Telescopes and their Enclousures~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~37.6 MB | PDF | 409 pages~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ *********************************************************************************** Radio telescopes as well as communication antennas operate under the influence of gravity, temperature and wind. Among those, temperature influences may degrade the performance of a radio telescope through transient changes of the focus, pointing, path length and sensitivity, often in an unpredictable way. Thermal Design and Thermal Behaviour of Radio Telescopes and their Enclosures reviews the design and construction principles of radio telescopes in view of thermal aspects CONTENTS *1 Radio Astronomy and Radio Telescopes* 1.1 Radio Wavelengths and Radio Telescopes 1.2 Deep Space Network and Large Communication Antennas 1.3 Radio Telescopes in Space 1.4 Overview of Telescope Constructions *2 Radio Telescope Constructions in View of Thermal Aspects* 2.1 Optical Configurations 2.1.1 The Parabolic Reflector 2.1.2 The Cassegrain and Gregory System 2.2 Basic Telescope Constructions 2.2.1 The Telescope with Alidade Support 2.2.2 The Telescope with Pedestal–Yoke Support 2.2.3 The Telescope with Pedestal–Fork Support 2.3 Telescope Components 2.3.1 Reflector Backup Structure (BUS) 2.3.2 The Homologous BUS 2.3.3 The Open and Closed, Ventilated and Climatised BUS 2.3.4 Reflector Panels 2.3.5 Active Reflector Surface 2.3.6 The Quadripod and Subreflector 2.3.7 The Secondary Focus Cabin 2.4 The Thermal Design of Radio Telescopes *3 Telescope Enclosures* *4 The Variable Thermal Environment* 4.1 The Environment and Observatory Sites 4.2 The Ambient Air 4.3 The Ambient Air Temperature 4.3.1 Measured Ambient Air Temperatures 4.3.2 Approximation of the Daily Ambient Air Temperature 4.3.3 Rate of Ambient Air Temperature Change 4.4 Wind Speed and Wind Direction 4.4.1 MeasuredWind Speeds 4.4.2 Wind Speed and Convective Heat Transfer 4.5 Ground Temperature 4.5.1 Measured Ground Temperatures 4.5.2 Approximation of the Ground Temperature 4.6 Humidity, Condensation, Icing 4.6.1 Humidity and Sky Radiation 4.7 Sky Temperature 4.7.1 Measured Sky Temperature 4.7.2 Calculation of the Sky Temperature 4.8 Cloud Coverage 4.9 Solar Radiation 4.9.1 Measurements of Solar Radiation 4.10 Meteorological Design Specifications 4.11 Space Environment . *5 Calculation of Solar Illumination* 5.1 The Apparent Motion of the Sun 5.2 The Plane Surface 5.3 The Tube Surface 5.4 The Parabolic Reflector Surface 5.4.1 Borderline between Shadow and Sunshine 5.4.2 Solar Illumination of the Reflector Surface 5.5 The Open and Closed BUS 5.6 The Box–type Enclosure (Astrodome) 5.7 The Cylindrical Enclosure (Astrodome) 5.8 The Over–Hemispherical Radome 5.9 Manipulation of Insolation through Surface Finish 5.10 Sun on Subreflector and Quadripod *6 Temperature Measurements and FEM Thermal Deformation* Calculations 6.1 Electric Resistance Temperature Sensors 6.2 Temperature Measurements by Infrared Radiation 6.3 Temperature Sampling Rate 6.4 Location of Temperature Sensors (InterpolationMatrix and InfluenceMatrix) 6.5 Precision of Temperature Measurements 6.6 Prediction of Temperature induced Deformations 6.7 Empirical Relations 6.8 Temperature related Measurements *7 Heat Transfer* 7.1 Laws of Thermodynamics and Modes of Heat Transfer 7.2 Amount of Heat transferred 7.3 Heat Content 7.4 Heat Transfer by Conduction 7.5 Heat Transfer by Convection 7.6 Heat Transfer by Conduction and Convection 7.7 The Convective Heat Transfer Coefficient (h) 7.7.1 Forced Convection 7.7.2 Natural Convection 7.7.3 Forced Convection and Ventilation 7.7.4 Natural Convection and Ventilation 7.8 Radiative Heat Transfer 7.9 Heat Transfer by Conduction, Convection and Radiation 7.10 Radiative Nodes and View Factors 7.10.1 Radiative Nodes 7.10.2 View Factor Relations 7.10.3 Internal View Factors 7.11 Energy/Heat Conservation 7.12 The Steady and Non–Steady Thermal State 7.12.1 External Thermal Time Constant t ext 7.12.2 Internal Thermal Time Constant t int (Conduction) *8 Radiative Coupling towards Sky and Ground* (External View Factor) 8.1 Vertical and HorizontalWalls 8.2 The Radome and Astrodome 8.3 The Parabolic Reflector 8.4 The Open and Closed BUS *9 Measured Thermal Behaviour of Radio Telescopes* 9.1 Telescope Supports 9.1.1 The Pedestal 9.1.2 The Alidade 9.1.3 The Fork Support 9.1.4 Path Length Variations of Telescope Supports (for radio interferometer and VLBI arrays) 9.2 BUS Supports 9.2.1 The (climatised) Yoke 9.2.2 The Central Hub 9.3 Backup Structures (BUS) 9.3.1 The Open BUS 9.3.2 The Closed BUS 9.3.3 The Ventilated BUS 9.3.4 Radial and Circular Ventilation 9.3.5 The Climatised BUS (IRAM 30–m Telescope) 9.3.6 Thermal Deformations and Active Reflector Surfaces 9.3.7 The Radome/Astrodome enclosed BUS 9.3.8 Temperature Changes of the BUS and Focus Changes 9.4 Panels 9.4.1 Experimental Data of Panel Temperatures 9.4.2 Panel Temperatures measured on Telescopes 9.4.3 Thermal Panel Buckling 9.4.4 Heated Panels, De–icing of Panels 9.5 Quadripod, Subreflector, Focus Cabins 9.5.1 Quadripod 9.5.2 Subreflector 9.5.3 Focus Cabins 9.6 Observations in the Direction of the Sun 9.7 De–icing of a Telescope 9.8 Measured Temperature Uniformity of Radio Telescopes 9.9 The measured Thermal Behaviour of Telescopes 9.10 TemperatureMonitoring and Trouble–Shooting 9.11 Other Thermal Effects *10 Measured Thermal Behaviour of Enclosures* *11 Thermal Model Calculations* 11.1 Mechanical Models of Structural Components 11.2 Static Thermal Calculations (TheUse of Known Temperature Distributions) 11.3 Dynamic Thermal Model Calculations (TheDerivation of TemperatureDistributions) 11.4 Node Structure of Thermal 11.5 The Thermal Environment as Input Data 11.6 Models of Panels 11.7 Model of Telescope Supports 11.7.1 Model of an Alidad 11.7.2 Model of a Yoke 11.7.3 Model of a Fork Support 11.8 Model of a Backup Structure 11.8.1 Model of an Open BUS 11.8.2 Model of a Closed BUS with Natural Ventilation 11.8.3 Model of a Closed BUS with Forced Ventilation 11.9 Model of a Radome and Closed Astrodome 11.10 Servo–loop Controlled Ventilation/Heating/Cooling 11.11 Model Calculations and Energy Balance 11.12 Model Calculations for Operational Purposes 11.13 Precision of Model Calculations 11.14 Programmes for Model Calculations *12 Beam Formation and Beam Degradation* 12.1 Wave Propagation and Beam Formation 12.2 The Perfect Radio Telescope 12.3 The Beam Pattern of the Perfect Radio Telescope 12.4 The Real Radio Telescope 12.4.1 Systematic Wavefront Deformations 12.4.2 Repetitive Wavefront Deformations (Thermal Panel Buckling) 12.4.3 RandomWavefront Deformations 12.5 Superposition of Random and Systematic (Thermal) Deformations 12.6 Beam Deformations and Thermal Tolerances *13 Thermal Tolerances* 13.1 Global Estimates of Temperature Influences 13.1.1 Reflector Diameter Estimates 13.1.2 Estimated Thermal Behaviour of a BUS 13.1.3 Estimated Thermal Behaviour of an Alidade/Fork Support 13.1.4 Estimated Thermal Behaviour of Panels 13.2 System Alignment Tolerances 13.2.1 Displacements and Tilts of Main Reflector and Subreflector 13.2.2 Temperature induced Pointing Errors 13.2.3 Alignment Errors: Temperature Tolerance Estimates 13.3 Random Reflector Errors 13.4 Design Specifications and Error Budget *14 Optical Telescopes and Enclosures* *15 A Summary and Further Studies* 15.1 A Summary of the Present State 15.2 Temperature Measurements and Dynamic Thermal Models 15.3 Further Studies 15.4 A Dynamic Thermal Error Budget for Design 15.5 A Fundamental Investigation of Radio Telescope/Antenna Constructions 15.6 Future Design =================================================================================== *********************************************************************************** **********In order to keep files alive please seed until a ratio of 1:1************ ****************************Thank you ~ Oceanhawk :)******************************* *********************************************************************************** ===================================================================================

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