NASA CR-134886 ER75-4368 MICROWAVE POWER TRANSMISSION SYSTEM STUDIES VOLUME III SECTION 8-MECHANICAL SYSTEMS AND FLIGHT OPERATIONS RAYTHEON COMPANY EQUIPMENT DIVISION ADVANCED DEVELOPMENT LABORATORY SUDBURY, MASS. 01776 prepared for NATIONAL AERONAUTICS AND SPACE ADMINISTRATION NASA Lewis Research Center Contract NAS 3-17835
1. Report No. NASA CR-134886 2. Government Accession No. 3. Recipient's Catalog No. 4. Title and Subtitle MICROWAVE POWER TRANSMISSION SYSTEM STUDIES Volume III - Mechanical Systems and Flight Operations (Section 8) 5. Report Date December 1975 6. Performing Organization Code 7. Author(s) O. E. Maynard, W.C. Brown, A. Edwards, J. T. Haley, G. Meltz J. M. Howell - Raytheon Co. ; A. Nathan - Grumman Aerospace Corp, 8. Performing Organization Report No. ER75-4368 10. Work Unit No. 11. Contract or Grant No. NAS 3-17835 13. Type of Report and Period Covered = Contractor Report 14. Sponsoring Agency Code 9. Performing Organization Name and Address Raytheon Company Equipment Division 528 Boston Post Road Sudbury, Massachusetts 01776 12. Sponsoring Agency Name and Address National Aeronautics and Space Administration Washington, D. C. 20546 15. Supplementary Notes Mr. Richard M. Schuh NASA Lewis Research Center Cleveland, Ohio 44135 16. Abstract A study of microwave power generation, transmission, reception and control was conducted as a part of the NASA Office of Applications1 joint Lewis Research Center/Jet Propulsion Laboratory five-year program to demonstrate the feasibility of power transmission from geosynchronous orbit. This volume (3 of 4) summarizes the efforts and presents recommendations associated with preliminary design and concept definition for mechanical systems and flight operations. Technical discussion in the areas of mission analysis, antenna structural concept, configuration analysis, assembly and packaging with associated costs are presented. Technology issues for the control system, structural system, thermal system and assembly including cost and man’s role in assembly and maintenance are identified. Background and desired outputs for future efforts are discussed. 17. Key Words (Suggested by Author(s)) Microwave power transmission; power from space; satellite power transmission; phased array power transmission; rectifying antenna (rectenna). 18. Distribution Statement Unclassified - Unlimited 19. Security Qassif. (of this report) Unclassified 20. Security Qassif. (of this page) Unclassified 21. No. of Pages 22 Price' 233 $3. 00
PREFACE This section was prepared by Grumman Aerospace Corporation for Raytheon as the final report on the Mechanical System and Flight Operations tasks of Preliminary Analysis and Concept Definition. The baseline MPTS assumed for these tasks was derived from the prior feasibility study (Reference 4). The principal difference between this baseline and the system description that evolved during the Conceptual Design Phase was the increase in weight of the MPTS waveguide to reflect an increase in wall thickness to 0.5 mm. This increase does not materially effect the study results since the structure design driver is the thermal environment, and the orbital transportation- assembly costs are normalized to cost per unit weight. A similar evolution to higher weight took place in the estimate for the solar photovoltaic power source used as an example for the complete SPS. The preliminary and final estimates are as follows for an aluminum-amplitron configuration and 5 GW ground output power:
TABLE OF CONTENTS VOLUME I - EXECUTIVE SUMMARY Section Page 1. Introduction 2 2. DC to RF Conversion 4 3. Transmitting Antenna and Phase Front Control 9 4. Mechanical Systems 16 5. Flight Operations 22 6. Receiving Antenna 25 7. Systems Analysis and Evaluation 28 8. Critical Technology 34 9. Critical Technology and Test Program 37 10. Recommendations for Additional Studies 42 VOLUME II - Sections 1 through 7 with Appendices A through G Page. 1. INTRODUCTION, CONCLUSIONS AND RECOMMENDATIONS 1.1 Introduction 1-1 1.2 Conclusions and Recommendations 1-3 1.2.1 General 1-3 1.2.2 Subsystems and Technology 1-5 1.2.2.1 Environmental Effects - Propagation 1-5 1.2.2.2 DC-RF Conversion 1-5 1.2.2.3 Power Interface and Distribution (Orbital) 1-7 1.2.2.4 Transmitting Antenna 1-7 1.2.2.5 Phase Front Control 1-8 1.2.2.6 Mechanical Systems and Flight Operations 1-9 1.2.2.7 Receiving Antenna 1-10 1.2.2.8 Radio Frequency Interference and Allocation 1-11 1.2.2.9 Risk Assessment 1-12 1.2.3 System Analysis and Evaluation 1-15
1.2.4 Technology Development and Test Programs 1-16 1.2.4.1 Technology Development and Ground Test Program 1-16 1.2.2 Technology Development and Orbital Test Program 1-16 1.2.5 Additional Studies 1-17 1.3 Report Approach and Organization 1-17 2. ORGANIZATION AND APPROACH 2.1 Organization 2- 1 2.2 Approach 2-3 3. ENVIRONMENTAL EFFECTS - PROPAGATION 3.1 Introduction 3-1 3.2 Atmospheric Attenuation and Scattering 3-2 3.2.1 Molecular Absorption 3-2 3.2.2 Scattering and Absorption by Hydrometeors 3-4 3.3 Ionosphere Propagation 3-12 3.3.1 Ambient Refraction 3-12 3.3.2 Scintillations Due to Ambient Fluctuations and Self-Focusing Instabilities 3-13 3.4 Ionospheric Modification By High Power Irradiation 3-19 3.5 Faraday Rotation Effects 3-21 3.5.1 Introduction 3-21 3.5.2 Diurnal and Seasonal Changes 3-21 3.5.3 Midlatitude Geomagnetic Storms 3-22 3.6 Conclusions and Recommendations 3-24 4. DC-RF CONVERSION 4.1 Amplitron 4- 1 4.1.1 RF Circuit 4-2 4.1.2 Pyrolytic Graphite Radiator 4-4 4.1.3 Magnetic Circuit 4-4 4.1.4 Controlling the Output of Amplitrons 4-5 4.1.5 Weight 4-5
4.1.6 Cost 4-7 4.1.7 Noise and Harmonics 4-7 4.1.8 Parameters Versus Frequency 4-9 4,1.9 Parameters Versus Power Level 4-15 4.2 Klystron 4-16 4.2.1 Periodic Permanent Magnetic Focusing 4-17 4.2.2 Circuit Efficiency 4-20 4.2.3 Klystron Efficiency With Solenoidal Focusing 4-25 4.2.4 Heat Dissipation and Beam Collection 4-27 4.2.5 Variations of Supply Voltages 4-34 4.2.6 Noise, Gain and Harmonic Characteristics 4-37 4.2.7 Tube Designs 4-40 4.2.8 Tube Lifetime 4-43 4.2.9 Weight and Cost 4-43 4.2.10 Conclusions 4-46 4.3 System Considerations 4-48 4.3.1 Amplitron Gain and Efficiency 4-48 4.3.2 Cascaded Vs Parallel Configurations 4-50 4.3.3 Cascaded Amplitron Gain 4-56 4.3.4 Amplifier Noise 4-56 4.3.5 Klystron Power Level 4-61 4.3.6 Converter Filter Requirements 4-64 4.4 Conclusions and Recommendations 4-69 5. POWER SOURCE INTERFACE AND DISTRIBUTION 5.1 Power Source Characteristics 5-1 5.2 Power Source-Converter Interface 5-3 5.3 Power Distribution Flow Paths 5-6 5.4 Magnetic Interaction 5- 12 5.5 DC to RF Converter Protection 5-15 5.6 Power Distribution System 5-19 5.7 Power Distribution Cost and Weight 5-23 5.8 Power Budget 5-24 5.9 Conclusions and Recommendations 5-24
6. TRANSMITTING ANTENNA 6.1 Aperture Illumination and Size 6-1 6.2 Array Types 6-10 6.3 Subarray Types 6-16 6.4 Subarray Dimensions 6-16 6.5 Subarray Layout 6-20 6.6 Tolerance and Attenuation 6-26 6.6.1 Frequency Tolerance 6-26 6.6.2 Waveguide Dimensional Tolerances 6-27 6.6. 3 Waveguide Attenuation 6-28 6.7 Mechanical Design and Analysis 6-29 6.7.1 Thermal Analysis and Configuration 6-29 6.7.2 Materials 6-38 6.7. 3 Transportation, Assembly and Packaging 6-43 6.8 Attitude Control and Alignment 6-47 6.9 Conclusions and Recommendations 6-49 7. PHASE FRONT CONTROL 7.1 Adaptive Phase Front Control 7-4 7.2 Command Phase Front Control 7-10 7.2.1 Phase Estimation 7-10 7.2.2 Bit Wiggle 7-14 7.3 Conclusions and Recommendations 7-14 APPENDIX A - RADIO WAVE DIFFRACTION BY RANDOM IONOSPHERIC IRREGULARITIES A. 1 Introduction A-1 A. 2 Model for Electron Density Irregularities A-2 A. 3 Phase Fluctuations and Their Spatial Correlation at the Diffracting Screen A-3 A. 4 Phase and Amplitude Fluctuations and Their Spatial and Temporal Correlation Functions on an Observational Plane A-4
APPENDIX B - SELF-FOCUSING PLASMA INSTABILITIES B-l APPENDIX C - OHMIC HEATING OF THE D-REGION C-l APPENDIX D - CAVITY CIRCUIT CALCULATIONS D.1 Input Impedance D-1 D.2 Input Power and Gain at Saturation D-2 D.3 Intermediate- and Output-Gap Voltages D-3 D.4 Cavity Tunings D-3 D.5 Output Cavity and Circuit Efficiency D-4 APPENDIX E - OUTPUT POWER OF THE SOLENOID-FOCUSED KLYSTRON E-l APPENDIX F - KLYSTRON THERMAL CONTROL SYSTEM F.1 Heat Conduction F-1 F.2 Temperature, Area and Weight of Radiators F-2 F.2.1 Collector F-3 F.2.2 Collector Reflector and Heat Shield F-4 F.2.3 Body Radiator F-4 F.2.4 Body Reflector and Heat Shield F-5 F.3 Weight of Heat Pipes F-5 APPENDIX G - CONFINED-FLOW FOCUSING OF A RELATIVISTIC BEAM C—1 VOLUME IH - MECHANICAL SYSTEMS AND FLIGHT OPERATIONS (Section Page 1. INTRODUCTION 1-1 2. SUMMARY 2.1 Task 1 - Preliminary Design 2-1 2.1. 1 Control Analysis 2-1 2.1.2 Thermal/Structural Analysis 2-1 2.1.3 Design Options and Groundrules for Task 2 Concept Definition 2-5
2.2 Task 2 - Concept Definition 2-9 2.2.1 Mission Analysis 2-9 2.2.2 Antenna Structural Definition 2-9 2.2.3 Configuration Analysis 2-14 2.2.4 Assembly 2-21 2.2.5 Cost 2-31 2.3 Recommendations 2-33 TECHNICAL DISCUSSION 3.1 Mission Analysis 3. 1-1 3.1 SSPS Configuration and Flight Mode Descriptions 3. 1-1 3.1.2 Transportation System Performance 3.1-1 3.1. 3 Altitude Selection 3. 1-8 3.1.4 SEPS (Ion Engine) Sizing 3. 1-14 3.2 Antenna Structural Concept 3.2-1 32. 1 General Arrangement 3. 2-1 3.2.2 Rotary Joint 3.2-1 3.2.3 Primary/Secondary Antenna Structure 3.2-15 3.2.4 Structure/Waveguide Interface 3.2-15 3.2. 5 Antenna Weight and Mass Properties 3. 2-18 3.3 Configuration Analysis 3.3-1 3.3.1 Control Analysis 3. 3-1 3.3.2 Thermal Evaluation 3. 3-9 3.3.3 Structural Analysis 3. 3-41 3.4 Assembly and Packaging 3.4-1 3.4.1 Detail Parts 3.4-1 3.4.2 Structural Assembly 3.4-9 3.5 Cost 3. 5. 1 3.5.1 Task 1 - Preliminary Design Results 3.5-1 3.5.2 Task 2 - Concept Definition Results 3. 5-5 3.5.3 MPTS Structural Costs 3. 5- 19
4. TECHNOLOGY ISSUES 4,1 Control System 4-1 4.1.1 Evaluation of Alternate Power Transfer and Drive Devices 4-1 4,1.2 Detailed Control System Analysis 4-2 4.2 Structural System 4-3 4.2.1 Composite Structures and Assembly Techniques 4-3 4.2.2 Tension Brace Antenna Feasibility Assessment 4-4 4.2.3 Local Crippling Stress Evaluation 4-4 4.2.4 Design Environments 4-5 4.2.5 Optimum Antenna Structures 4-5 4.2.6 Finite Element Model Development 4-6 4.2.7 Composite Waveguide 4-6 4.3 Thermal System 4-7 4.3.1 Maximum Temperature 4-7 4.3.2 Transient Analysis 4-8 4.4 Assembly 4-9 4.4.1 Assembly Cost 4-9 4.4.2 Man’s Role in Assembly and Maintenance 4-10 5. REFERENCES 5-1 VOLUME IV - Sections 9 through 14 with Appendices H through K 9. RECEIVING ANTENNA 9.1 Microwave Rectifier Technology 9- 1 9.2 Antenna Approaches 9-9 9.3 Topology of Rectenna Circuits 9-14 9.4 Assembly and Construction 9-21 9.5 ROM Cost Estimates 9-21 9.6 Power Interface Estimates 9-25 9.6.1 Inverter System 9~30 9.6. 2 Power Distribution Costs 9-30 9.6.3 System Cost 9-31 9. 7 Conclusions and Recommendations 9-31
10. FREQUENCY INTERFERENCE AND ALLOCATION 10-1 10.1 Noise Considerations 10-3 10.1.1 Amplitron 10-3 10.1.2 Klystron 10-4 10.1.3 Interference Limits and Evaluation 10-6 10.2 Harmonic Considerations 10-6 10.3 Conclusions and Recommendations 10-12 11. RISK ASSESSMENT 11.1 Technology Risk Rating and Ranking 11-1 11.2 Technology Assessment Conclusions and Recommendations 11-16 12. SYSTEM ANALYSIS AND EVALUATION 12- 1 12.1 System Geometry 12-1 12.2 Parametric Studies 12-3 12,2.1 System Relationships 12-3 12.2.2 Efficiency, Weight and Cost 12-8 12.2.3 Converter Packing 12-12 12.2.4 Capital Cost Vs Power and Frequency Results 12-13 12. 2.5 Ground Power Density and Power Level Selection 12-19 12.2. 6 Frequency Selection 12-22 12.2.7 Characteristics of 5 GW and 10 GW Systems 12-22 12.2.8 Energy Cost 12-36 12.3 Final System Estimates 12-41 12.3.1 Cost and Weight 12-41 12.3.2 Efficiency Budget 12-43 12.3.3 Capital Cost and Sizing Analyses 12-45 12.4 Conclusions and Recommendations 12-45 13. CRITICAL TECHNOLOGY AND GROUND TEST PROGRAM 13.1 General Objectives 13-1 13.2 Detailed Ground Test Objectives 13-2 13.3 Implementation - Ground Test 13-3 13.3.1 Summary 13-3
13.3.2 Phase I 13-5 13.3.3 Phase II 13-5 13.3.4 Phase III 13-9 13.3.5 Alternate Phase I Converter Implementation 13-11 13.4 Critical Technology Development 13-14 13.4.1 Amplitron 13-14 13.4.2 Klystron 13-14 13.4.3 Phase Control 13-14 13.5 Schedule and Cost 13-15 13.6 Conclusions and Recommendations 13-17 14. CRITICAL TECHNOLOGY AND ORBITAL TEST PROGRAM 14.1 Orbital Test Objectives 14-1 14.2 Implementation 14-3 14.2.1 Geosatellite (Mission 1) 14-4 14.2.2 Shuttle Sorties (Missions 2 through 11) 14-4 14.2.3 Orbital Test Facility 14-23 14.3 Cost and Schedule 14-25 14.4 Conclusions and Recommendations 14-30 APPENDIX H - ESTIMATED ANNUAL OPERATIONS AND MAINTENANCE COST (5 GW System) H-1 APPENDIX I - ANNUAL OPERATIONS AND MAINTENANCE COST (10 GW System) I-1 APPENDIX J - SYSTEM ANALYSIS EXAMPLES J. 1 Introductory Analysis of Initial Operational System With Minimum Size Transmitting Antenna J-1 J. 2 Analysis of the Final Operational System and Their Goals J-10 J. 3 Analysis of the Initial Operational System Based On the Final System Configuration J-21 J. 4 Weight and Cost Analysis for the Initial and Final Operational Systems J-25 J. 5 Energy Cost J-27
APPENDIX K - DETAILS OF GROUND AND ORBITAL TEST PROGRAM K.1 Introduction K- 1 K.2 Objectives Implementation Equipment and Characteristics K-l K.3 Implementation of Objectives Hl, H2, DI and D2 Using Low Earth Orbit Sortie Missions K-3 K.4 Defining an MPTS Orbital Test Facility Program K-13 K.4.1 Assumptions K-13 K.4.2 Sizing the Phased Array Antennas K-14
ILLUSTRATIONS Figure Page 1-1 Preliminary Design Option Matrix........................................................... 1-3 1-2 Task 1 - Preliminary Design Study Logic, Mechanical Systems and Flight Operations..................................................................................... 1-3 1-3 Task 2 - Concept Definition Study Logic ................................................ 1-4 2-1 Control System Requirements..................................................................... 2-2 2-2 Control System Requirements..................................................................... 2-2 2-3 Mechanical System Options Recommended for Task 2 Study............. 2-4 2-4 Antenna Geometry Tradeoff ....................................................................... 2-6 2-5 Power Level Limitations Due to Material Thermal Properties . . 2-6 2-6 Temperature Difference Between Structural Member Located Different Distances Above the Antenna Surface................................... 2-7 2-7 Task 2 Baseline Design Guidelines ......................................................... 2-8 2-8 Level 1 Assembly Functional Flow............................................................ 2-10 2-9 Baseline SSPS................................. 2-10 2-10 Mission Options ............................................................................................... 2-11 2-11 SSPS Orbital Decay Due to Aerodynamic Drag....................................... 2-12 2-12 Antenna Structural Arrangement ............................................................... 2-13 2-13 Rotary Joint.............................. 2-15 2-14 Structure/Waveguide Interface..................................................................... 2-16 2-15 Structural Joints..................... 2-17 2-16 Comparison of Maximum Termperature and Thermal Gradients . . 2-18 2-17 Temperature Difference Between Beam Cap Members Located Different Distances Above Antenna Surface ................ 2-20 2-18 Waste Heat Flux at Center of Antenna as Function of Scale Factor.............................................................................. 2-20 2-19 Cross-Section Design...................................................................................... 2-22 2-20 Range of Thermally Induced Deflections and Local Slope................... 2-23 2-21 Structural Detail Parts Assembly Options.............................................. 2-24 2-22 Detail Part Assembly Summary.................................................................. 2-24 2-23 MPTS Antenna Structural Assembly.......................................................... 2-26 2-24 Assembly Operations Analysis Approach................................................. 2-27 2-25 Summary of Assembly Options..................................................................... 2-28 2-26 Transportation and Assembly Elements ................................................. 2-29
2-27 Transportation and Assembly System Fleet and Support Equipment Characteristics and Cost Summary................................... 2-30 2-28 Traffic and Fleet Size Summary .............................................................. 2-32 2-29 Assembly Cost Comparison ....................................................................... 2-32 2-30 Antenna Structural Cost Comparison ..................................................... 2-34 2-31 Recommendations for Task 3 Study ......................................................... 2-34 3.1-1 SSPS Baseline Configuration....................................................................... 3.1-2 3.1-2 SSPS Mass Properties................................................................................... 3.1-3 3.1-3 Mission Options ............................................................................................... 3.1-4 3.1-4 Shuttle Payload Capability - Due East Launch from KSC................... 3.1-6 3.1-5 Shuttle Payload Capability - Due East Launch from KSC................... 3.1-6 3.1-6 Cryogenic Tug Deploy Performance......................................................... 3.1-7 3.1-7 Cryogenic Tug Configuration........................................................................ 3.1-7 3.1-8 Ion Propulsion Altitude vs Time From (100 n mi circular) - No Plane Change..................................................................... 3.1-9 3.1- 9 SSPS Orbit Decay............................................................................................... 3.1-11 3.1- 10 SSPS Orbit Decay Characteristics ............................................................ 3.1-12 3.1- 11 SSPS Orbit Decay Characteristics ............................................................ 3.1-12 3.1- 12 Force Required to Compensate for Air Drag . .. .................................. 3.1-13 3.1- 13 Ion Propulsion System Sizing Factors...................................................... 3.1-15 3.1- 14 Optimum Specific Impulse.............................................................................. 3.1-17 3.1- 15 Maximized Payload Ratio.............................................................................. 3.1-17 3.2-1 MPTS Antenna Structural Arrangement.................................................... 3.2-3 3.2-2 MPTS Antenna Structural Arrangement....................................................... 3.2-4 3.2-3 Gear System........................................................................................................ 3.2-5 3.2-4 Typical Motor Options.................................................................................... 3.2-7 3.2-5 Rotary Drive Concept....................................................................................... 3.2-8 3.2-6 Antenna Rotary Joint....................................................................................... 3.2-9 3.2- 7 Power Transfer Device Selection Considerations ................................ 3.2-11 3.2- 8 Brush/Slip Ring Concept .............................................................................. 3.2-11 3.2- 9 Operating Temperatures (°C) of Candidate Brushes............................. 3.2-12 3.2- 10 Voltage Drop for Candidate Brushes (For Single Contacts).............. 3.2-12 3.2- 11 Friction and Wear Properties of Oils (Four-Ball Test)....................... 3.2-14
3.2-12 Friction and Wear Properties of Greases (Four-Ball Test)............. 3.2-14 3.2-13 Structural Members......................................................................................... 3.2-16 3.2-14 Waveguide/Structure Interface, Single Point Support......................... 3.2-17 3.2-15 Waveguide/Structure Interface, Three Point Support......................... 3.2-17 3.2-16 Antenna Structure Weight Summary (Graphite/Epoxy) Triangular Hat........................................................................ 3.2-19 3.2-17 Antenna Weight Comparison (Aluminum vs Composites Tubular Section)..................................................................... 3.2-20 3.2-18 Antenna Weight Comparison (Aluminum vs Composites Triangular Hat Section) ...................................................... 3.2-20 3.2-19 Structure Weight vs Antenna Dimension................................................... 3.2-22 3.2- 20 SSPS Microwave Antenna Mass Properties............................................. 3.2-23 3.2-21 Antenna Structure Weight............................................................................. 3. 2-24 3.2-22 Primary Structure (Upper Caps).................................................................. 3.2-26 3.2-23 Primary Structure (Posts)............................................................................. 3.2-27 3.2-24 Primary Structure (Lower Caps)............................................................... 3.2-28 3.2-25 Primary Structure Integration Items .. .................................................... 3.2-28 3.2-26 Secondary Structure.............................................................. 3.2-29 3.2-27 Secondary Structure Integration Items...................................................... 3.2-29 3.2-28 Elevation Joint Support................................................................................... 3.2-30 3.2-29 Elevation Yoke.................................................................................................. 3.2-31 3.2-30 Azimuth Yoke Support ................................................................................... 3.2-32 3.2-31 Azimuth Yoke..................................................................................................... 3.2-33 3.2-32 Mechanisms and Support................................................................................. 3.2-34 3.2-33 Rotary Joint Drive (Mechanical vs Linear Induction Motor) ..... 3.2-34 3.3-1 System Torque Environment........................................................................ 3.3-2 3.3-2 Microwave Antenna Mechanical Pointing System.................................. 3.3-3 3. 3-3 SSPS Bending Mode Data................................................................................. 3. 3-5 3.3-4 Servomechanism Environment..................................................................... 3.3-6 3. 3-5 Slip Ring Friction Torque.............................................................................. 3.3-8 3.3-6 Control System Requirements..................................................................... 3.3-8 3.3-7 Preliminary Design Control System.......................................................... 3.3-10 3.3-8 Antenna Support Structure.............................................................................. 3.3-11 3.3-9 Gaussian Radiative Heat Flux From Antenna Surface.......................... 3.3-13
3.3-10 Maximum Structural Temperature vs Transmitted Power............. .. 3.3-14 3.3-11 Microwave Power Transmission System Structure ............................ 3.3-16 3.3-12 Beam Cap Element Geometries.................................................................. 3.3-17 3.3-13 Typical Thermal Model for Structural Member..................................... 3.3-18 3.3-14 Maximum Tube Temperature as a Function of Antenna Surface Temperature With Tube Inner Wall Emissivity as a Parameter . . 3.3-19 3.3-15 Maximum Temperature Difference Across a Tubular Structural Member as a Function of Antenna Surface Temperature With Tube Inner Wall Emissivity as a Parameter................ 3.3-21 3.3-16 Thermally Induced Stresses and Minimum Wall-to-Radius Ratios for Tubes..................................................................... 3. 3-21 3.3-17 Comparison of Temperature Profiles in High-Hat Section for . ., = 0.9 and 0.1......................................................... 3.3-23 inside 3.3-18 Temperature Distribution Within Triangular Shaped Structural Member............................................................... 3.3-24 3.3-19 Maximum Temperature and Temperature Difference in Triangular Member............................................................... 3.3-26 3.3-20 Comparison of Maximum Temperature for Different Beam Cap Element Geometries ........................... 3.3-28 3.3-21 Comparison of Maximum Temperature Difference for Various Geometries............................................................... 3.3-28 3.3- 22 Temperature Distribution in a Beam Cap Member Located 1 Meter Above Antenna Surface............................... .. 3.3-29 3.3-23 Temperature Distribution in a Beam Cap Member Located 1 Meter Above Antenna Surfacee................................................................ 3. 3-30 3.3- 24 Temperature Difference Between Beam Cap Members Located Different Distances Above Antenna Surface.................... 3.3-33 3.3- 25 Temperature Difference Between Beam Cap Members Located Different Distances Above Antenna Surface................... 3.3-33 3.3- 26 Column Temperatures.................................................................................. 3.3-36 3.3- 27 Waste Heat Flux at Center of Antenna as Function of Scale Factor ........................................................................... 3.3-36 3.3-28 Waste Heat Profile for Various Values of Scale Factor.................... 3. 3-37 3.3-29 Maximum Temperatures as a Function of Scale Factor.................... 3. 3-39 3.3-30 Thermal Performance of MPTS With and Without Heat Pipes . . . 3.3-40 3.3-31 Alternate Structural Arrangements.......................................................... 3.3-42 3.3-32 Weight Relationship for Different L/D (Length Tube/Diameters) . 3.3-43
3.3-33 Strength of Circular Tubes for Various Axial Compression Loads as Function of Wall Thickness and Diameter.. 3.3-45 3.3-34 Strength of Circular Tubes for Various Axial Compression Loads as Function of Wall Thickness ............. 3.3-45 3.3-35 Tri-Beam Cap Cross-Sections (Graphite/Epoxy)................................. 3.3-46 3.3-36 Design Loads.................................................................................................... 3.3-47 3.3-37 Deflections - Preliminary Assessment................................................... 3.3-47 3.3-38 Typical Antenna Deflections Due to Thermal Gradients ........ 3.3-49 3.3-39 Typical Slopes of Structure Due to Thermal Gradients...................... 3.3-49 3.3-40 "Egg Crate" Secondary Structure Deflection Slopes (108 Meter Section)............................................................... 3.3-50 3.3-41 Estimated Graphite Composite Properties............................................. 3.3-52 3.3-42 Thermal Stability of Various Adhesives at 533°K................................. 3.3-52 3.3-43 Cost and Processing Characteristics of Various Types of Adhesives.............................................................................. 3.3-54 3.3-44 Comparison of Material Properties ......................................................... 3.3-54 3.4-1 Structure Detail Parts Assembly Options................................................ 3.4-2 3.4-2 Characteristics of Articulated Lattice Beam.......................................... 3.4-3 3.4-3 Tri-Beam Layout Using Tabular and Solid Element Caps.................. 3.4-4 3.4-4 Allowable Column Load vs Diameter......................................................... 3.4-6 3.4-5 Shuttle Compatibility Packaging.................................................................. 3.4-6 3.4-6 Inflight Detail Parts Assembly..................................................................... 3.4-7 3.4-7 Support Equipment Requirements for Inflight Assembly of Tri-Beams ...................................................................................................... 3.4-8 3.4-8 Auto In-Orbit Manufacture (Aluminum)................ ................................... 3.4-8 3.4-9 Level 2 Functional Flow: Assemble MPTS.............................................. 3.4-10 3.4-10 Level 3 Functional Flow: Assemble Rotary Joints (3 Sheets) .... 3.4-11 3.4-11 Level 3 Functional Flow: Assemble Rotary Joint to Antenna Interface Structure ........................................................................................ 3.4-14 3.4-12 Level 3 Functional Flow: Assemble Primary/Secondary Structure . .. .............................................................................. 3.4-14 3.4-13 Level 4 Functional Flow: Assemble Lower Cap; Primary Structure........................ ... ....................................................... 3.4-16 3.4-14 Assembly Timeline and Consumables Requirement............................. 3.4-17 3.4- 15 Manipulator Performance Complexity Factor........................................ 3.4-19
3.4-16 Manipulator Module Assembly Operations Summary........................... 3.4-19 3.4-17 Level 4 Functional Flow: Assemble Lower Cap; Primary Structure.................................................................................... 3.4-21 3.4-18 Detailed Task Sequence and Performance Times for Two-Man Skylab 3 Twin-Pole Sunshade EVA Deployment........... 3.4-22 3.4-19 EVA Assembly Operations Summary........................................................ 3.4-22 3.4-20 Free-Flying Teleoperator Concept........................................................... 3.4-24 3.4-21 Low Altitude Assembly Support Equipment Weight and Cost Estimates........................................................................ 3.4-24 3.4-22 High Altitude Assembly, Typical Six-Man Support Space Station. . 3.4-27 3.4-23 High Altitude Assembly, Typical 12-Man Support Space Station . . 3.4-27 3.4-24 Manned Transport Module........................................................................... 3.4-28 3.5-1 Task 1 - Preliminary MPTS Design Data Sheet, Rectangular Grid............................................................................................... 3.5-3 3.5-2 Task 1 - Preliminary MPTS Design Data Sheet, Radial Spoke . . . 3.5-4 3.5-3 Transportation and Assembly Cost Comparison Cases...................... 3.5-6 3.5-4 SSPS Weights..................................................................................................... 3.5-6 3.5-5 Traffic Model Assessment, Flight Plan 1 ................ ............................. 3.5-8 3.5-6 Traffic Model Assessment, Flight Plan 3 ............................................. 3.5-9 3.5-7 Level 1 Functional Flow: Assembly............................................................ 3.5-9 3.5-8 Traffic Model and Flight Size Assessment, Flight Plan 2................ 3.5-11 3.5-9 Traffic Analysis Summary............................................................................. 3.5-13 3.4-10 Transportation and Assembly Cost, Flight Plan 1............................... 3.5-13 3.5-11 Transportation and Assembly Cost, Flight Plan 2........................ 3.5-14 3.5-12 Transportation and Assembly Cost, Flight Plan 3............................... 3.5-15 3.5-13 Transportation and Assembly System Fleet and Support Equipment Characteristics and Cost Summary................................... 3.5-16 3.5-14 Waveguide Weight and Packaging Densitj7............................................... 3.5-18 3.5-15 Traffic Requirements as a Function of Waveguide Weight and Packaging Density.................................................................. 3.5-20 3. 5-16 Transportation and Assemblj- Cost Sensitivity to Waveguide Packaging Density.................................................................. 3.5-20 3. 5-17 Materials and Processing Costs.................................................................. 3. 5-22 3.5-18 MPTS Structural Cost Estimate Assumptions........................................ 3.5-24 3.5-19 MPTS Structural Concept Comparison .................................................... 3.5-24
LIST OF NON-STANDARD TERMS AFCRL Air Force Cambridge Research Laboratory ATC Air Traffic Control ATS Applications Technology Satellite CFA Crossed Field Amplifier CPU Central Processor Unit GaAs Gallium Arsenide HLLV Heavy Lift Launch Vehicle Met Meteorological MPTS Microwave Power Transmission System MW Microwave N. F. noise factor PPM periodic permanent magnet ROM Rough Order of Magnitude SCR Silicon Controlled Rectifier SEPS Solar Electric Propulsion Stage Sm-Co(SMCO) Samarium Cobalt SPS Satellite Power System SSPS Satellite Solar Power Station TDRS Tracking and Data Relay Satellite TEC Total Electron Content
Section 1 INTRODUCTION The objective of the Grumman study effort is to provide refined inputs for mechanical systems, structure and thermal control for Raytheon’s overall investigation of the Microwave Power Transmission System (MPTS). This system will be used to transmit, receive and control large amounts of power from space. Grumman’s efforts identified structural design options, the driver parameters for both weight and cost, and established requirements for the structural and flight operations systems. An orbiting electric power station has several major elements: the power source or converter, the electrical power distribution system and the microwave generator/ transmitting antenna. An antenna can be hypothesized that would be independent of the power source except for the mechanical control system interface. The purpose of Task 1, Preliminary Design, was to evaluate this mechanical interface. To achieve the depth needed to gain an understanding of accuracy and stability, a power source and spacecraft had to be selected. Because more data on physical characteristics were available on the Satellite Solar Power Station (SSPS), this power source/spacecraft was used in the preliminary assessment. Selection of the antenna structure required evaluation of 1) basic antenna geometry, 2) the impact of MW conversion thermal waste on structural material selection and feasible structural flatness, and 3) the mode of transportation and assembly. A broad matrix of antenna geometries, structural materials and transportation modes have been evaluated. Figure 1-1 summarizes this matrix of design options considered during the Task 1 Preliminary Design Phase. The three materials, aluminum, graphite/epoxy and Kevlar polyimide, were selected on the basis that they represent a broad range of strength, weight, cost and thermal characteristics. Aluminum represents a low cost, high weight option that would thermally limit the power level selected for the system. Graphite/epoxy represents a material with excellent thermal expansion characteristics, high strength and low weight. Kevlar polyimide would be low weight at modest cost with a resin that could withstand a high temperature environment.
The four transportation modes selected for Task 1 represent the near term Space Transportation System capabilities. A Transtage was selected, both in an expendable and reusable version, as being most representative of the performance of the Interim Upper Stage (IUS). A Full Capability Cryo Tug was used to represent the STS performance capability in the 1984 time frame. The fourth option, Shuttle/Low Altitude Assembly, was introduced into the matrix to determine the impact of assembly altitude on overall system selection. Antenna geometry options include a rectangular grid and a radial spoke structural layout. Both these structural arrangements are acceptable in terms of available layouts for the power distribution system. Antenna diameters between 0.7 to 1.4 km were included in the design matrix after Raytheon’s preliminary results indicated that optimum system performance would fall within these bounds. The Task 1 study logic for control analysis and thermal structural analysis and cost parametrics are outlined in Fig. 1-2. The output of the three principal tasks are recommendations for a limited number of control system, structural and flight operations options for detailed concept definition in Task 2. The limited number of design options recommended in Task 1 were evaluated in greater detail in Task 2, Concept Definition, using the study logic shown in Fig. 1-3. Information generated during Concept Definition will permit Raytheon to carry out technical and economic evaluation leading to selection of a single configuration to be the basis for ground demonstration test. Flight plans were generated for assembly of the SSPS at a low altitude which is within the performance range of the Shuttle with integral OMS, and at an altitude above the Van Allen belts. Traffic rates and fleet size requirements were established for a one and two year assembly period. Packaging densities of SSPS components were considered in establishing the method of assembly using manipulative devices, maneuvering units, and EVA. Assumptions concerning degree of human skills are outlined as well as the potential capability of support ancillary equipment. Sensitivity analysis of various levels of ground prefabrication compared to corresponding levels of orbital assembly was performed to determine the most cost effective approach to structural assembly.
Fig. 1-1 Preliminary Design Option Matrix Fig. 1-2 Task 1 Preliminary Design Study Logic, Mechanical Systems and Flight Operations
Fig. 1-3 Task 2 — Concept Definition Study Logic
Antenna general arrangements, interface drawings and weight statements are included in this document for use during the remainder of the MPTS studies. Detail thermal and structural evaluations have been performed to determine the limitations the structure impose on electronic layout and phase front control concepts. Mechanical options to a fully electronic control system have been identified and are shown to desensitize the tolerance on structural assembly accuracy and impact of thermal deflections over a wide range of sun-to-spacecraft geometries.
Section 2 SUMMARY 2.1 TASK 1 - PRELIMINARY DESIGN 2.1.1 Control Analysis Qualitative estimates of requirements and design options for antenna mechanical steering indicates that pointing accuracy of better than 1 arc-min can be achieved. The mechanical system, if integrated with the electronics microwave beam phase front control, could improve overall system efficiency with minimal impact on system weight and cost. Figure 2-1 summarizes the design environment for mechanical steering. The antenna gravity gradient torques are a major externally induced disturbance. Other factors, such as torque caused by solar pressure, or electromagnetic forces, are small. The most significant torque is the friction torque at the rotary joint. This torque varies as a function of system power level and power transfer technique. Base motions of the SSPS are caused by normal limit cycle operations and by solar array bending dynamics. Figure 2-2 is a composite of system accuracy and torque requirements as a function of mechanical control system frequency. An azimuth accuracy of 40 arc-sec can be achieved with a control system frequency of 1 rad/sec. This control frequency would require 1, 020, 000 N*m (750, 000 ft-lb) peak control torque (measured on load side of the gear train). This control system frequency is well above the first structural frequency of the SSPS and antenna. Peak horsepower requirements at 1 rad/sec is 0.18 and 1.75 hp in azimuth (East-West rotation) and elevation (North-South rotation), respectively. A review of top level methods for implementing mechanical steering favors a motorgearing mechanical system as opposed to a reaction jet system. Because control system frequencies are well above the first structural bending frequencies, no instabilities are foreseen. A mechanical system could be configured against wear by providing sufficient redundancy. The reaction jet approach, in which jets are mounted to the antenna, would be advantageous because the antenna structure could be more readily isolated from spacecraft dynamics than a mechanical system using gear trains. The shortcomings of the jet system, however, include:
Fig. 2-1 Control System Requirements Fig. 2-2 Control System Requirements
• Requirement for propellant resupply • Contamination of waveguide functions. Figure 2-3 lists mechanical system options considered in Task 1 and identifies configurations recommended for Task 2 Concept Definition. Also included in Fig. 2-3 are recommended technology studies which could provide a more optimum design. Power clutches or rotary transformers are power transfer advanced space techniques that could lead to a reduction in interface friction, and increased life. Spur gears are recommended for the gear train, but a direct drive motor system would eliminate gears and may be easier to implement, provided sufficient accuracy could be achieved. Individual rollers are recommended as baseline because of ease of implementation. Ball bearings offer an advantage in terms of lower friction torques and should be considered as an alternate. DC brush torque motors are recommended; however, linear induction motors may show advantages in terms of life and inherent capability to isolate the spacecraft dynamics from the antenna dynamics. 2.1.2 Thermal/Structural Analysis A thermal/structural analysis has been carried out to determine deformations to be used in establishment of requirements for phase front control, and to determine cost and weight factors for overall system selection. 2.1.2.1 Preliminary Design Options Figure 2-4 is a weight comparison of principal structural design layouts. The rectangular grid approach was found to be lighter than the radial spoke arrangement. Two compression member designs were considered; a singular tube, 100 m long, and a triangular girder with thin walled circular tubes at the apex with cross tubes and diagonal wire bracing. The triangular girder approach was found to be significantly lighter than the singular tube. Assessment of structural deflections included analysis of load, thermal and assembly tolerance induced deformations. The assembly tolerances were found to be the largest source of deformation with a worst case tip deflection of 0.17 degree. Deflections due to thermal bending can be kept below 1 arc-min if thermal gradients between the upper and lower primary structural caps can be controlled to less than 4°K. Deflections due to loads were found to be insignificant.
Fig. 2-3 Mechanical System Options Recommended for Task 2 Study
2.1.2.2 Thermal Evaluation Preliminary thermal analysis of the MPTS centered about studies that would indicate the sensitivity of temperature level and thermal gradient on antenna size, power level, microwave converter selection, and distribution. 2.1.2.2.1 Temperature Level - Structural temperature levels, material and antenna size combine to place limitations on the power that can be transmitted by the antenna. Figure 2-5 shows the limit power level for antenna diameters between 0.7 and 1.4 km. Aluminum, epoxy and polyimide are shown as representative materials. Aluminum and graphite/epoxy lose their strength characteristics at approximately 450°K. This limits system power levels for 1 km diameter antenna to 17 gw with a 90% efficient microwave converter and to 4 gw with a 70% efficient converter. Limit power levels can be significantly increased with the use of polyimide composite materials. 2.1.2.2. 2 Thermal Gradient - Figure 2-6 presents the thermal gradients between primary structural caps for distances of 40 and 90 meters. The trend indicates that to limit tip deflections to less than 1 arc-min, the average distance between caps should be somewhat less than 40 meters. This would keep temperature gradients below 4°C. The worst case thermal gradients occur when the antenna microwave surface shades the structure from the sun. 2.1.3 Design Options and Groundrules for Task 2 Concept Definition Task 1 resulted in recommendations that a frequency of 2.45 GHz be selected and four configurations of slotted waveguide transmitting arrays be studied in Task 2. These configurations involve combinations of amplitrons with aluminum structure and array, amplitrons with graphite composite structure and array, and a klystron with the same two materials. Task 1 also showed that a 5 gw ground output power level would be a reasonable choice for all Task 2 study vehicles. An antenna diameter of 1 km was selected based on the relative insensitivity of this parameter to overall system cost and performance. Figure 2-7 summarizes the guidelines for Task 2 study.
Fig. 2-4 Antenna Geometry Tradeoff Fig. 2-5 Power Level Limitations Due to Material Thermal Properties
Fig, 2-6 Temperature Difference Between Structural Member Located Different Distances above the Antenna Surface
Fig. 2-7 Task 2 Baseline Design Guidelines
2.2 TASK 2 - CONCEPT DEFINITION 2.2.1 Mission Analysis The mission analysis effort objective was to define flight scenarios for subsequent assessment of transportation system performance requirements. Figure 2-8 is a top level functional flow of the SSPS assembly sequence. Two flight plans for assembly and transport to geosynchronous orbit were developed: • Low altitude assembly and transport to geosynchronous using solar electric propulsion (SEP) • Assembly just above Van Allen belts and transport to geosynchronous using SEP. A baseline SSPS, Fig. 2-9 was assumed for mission analysis and subsequent estimates of traffic models and fleet sizes. Performance capabilities of the transportation system are summarized in Fig. 2-10. Shuttle performance of 65, 000 lb (29,400 Kg) can be expected up to an altitude of 190 n mi. The Cryo Tug, used in the flight plan with assembly at 7000 n mi, has a payload capability of 36, 800 lb (16,700 Kg) in a Tug recoverable mode. SEP size and performance data for the two flight modes are presented in Fig. 2-10. A SEP system efficiency of 0.7 and a specific weight of 15 Ib/kw (6. 8 Kg/kw) was assumed in the stage sizing. The 0.7 efficiency is equaled or exceeded by today’s technology. Overall system specific weight is consistent with projected solar cell weights for the SSPS itself. Specific weight of the power conditioning and subsystems is based on a projected four fold improvement in technology (using today’s technology would result in an overall system specific weight of ). A 190 n mi assembly site would require continuous orbit keeping propulsion to compensate for air drag. Figure 2-11 indicates that uncorrected air drag effects would result in assembly entry after one to 16 months depending upon configuration . The spread in is indicative of the SSPS configuration with solar blankets deployed and retracted. A 16-lb thrust (70 newton) SEP stage would be required for the orbit keeping function. A propellant expenditure of 44 Klb (20, 000 Kg) is projected. 2.2.2 Antenna Structural Definition The MPTS antenna is 1 km in diameter by 40 meters deep. Fig. 2-12. The antenna is assembled in two rectangular grid structural layers. The primary structure is built-up in 108 x 108 x 35 meter bays using triangular girder compression members 18 meters long
Fig. 2-8 Level 1 Assembly Functional Flow Fig. 2-9 Baseline SSPS
Fig. 2-10 Mission Options
Fig. 2-11 SSPS Orbital Decay Due to Aerodynamic Drag
Fig. 2-12 Antenna Structural Arrangement
and 3 meters deep. The secondary structure is used as support points for the waveguide subarrays and is built up as 18 x 18 x 5 meter bays. The total antenna structure/mechanical system weight is using aluminum and using graphite/epoxy (or polyimide). The antenna-to-spacecraft interface uses a 360° rotary joint for antenna motion perpendicular to the orbit plane (azimuth joint) and a limited motion rotary joint, ± 10 deg, for North-South pointing (elevation joint), Fig. 2-13. Two slip ring assemblies (one for plus power and one for power return) are used for power transfer across the azimuth rotary joint and flex cable is used across the elevation joint. Both the azimuth and elevation joint drive assemblies utilize a geared rail about the diameter of the support structure and four DC brushless motor driven roller assemblies. The structure to waveguide interface uses three gimballed screw jack assemblies (Fig. 2-14) to provide a mechanical tuning system for alignment of the waveguides after construction. Up to 40. 5 cm of linear motion can be used to correct thermally induced antenna tip deflections and can also be used to correct a maximum expected 4 arc-min subarray misalignment. Figure 2-15 is a typical conceptual design of a mechanical locking mechanism for structural joints. The girder interconnect fitting is similar to a docking drogue which utilizes a spring-loaded ball lock for fastening with the tri-beam end fitting. 2.2.3 Configuration Analysis 2.2.3.1 Thermal Analysis A refined thermal analysis of the antenna conceptual design concentrated efforts on the following: • Selection of the tri-beam element longeron cross section to minimize maximum temperature and thermal gradients • Identifying the limit waste heat at the center of the antenna as a function of structural vertical member material • Defining range of thermal gradients between primary and secondary structural caps as a function of sun position relative to the antenna Figure 2-16 presents the maximum temperatures and thermal gradient across three candidate structural cross sections: tubular, rectangular hat, and triangular hat. The tube is the worst from a thermal standpoint. The use of aluminum tubing near the center
Fig. 2-13 Rotary Joint
Fig. 2-14 Structurt/Waveguide Interface
Fig. 2-15 Structural Joints
Fig. 2-16 Comparison of Maximum Temperature and Thermal Gradients
of the antenna will not be possible with this geometry. The rectangular high hat design is not an attractive structural geometry but does offer an improved temperature picture. The triangular hat design has the lowest maximum temperature level and minimum gradient of the concepts considered. Aluminum construction of the tri-beam horizontal members can be considered with this cross section. The temperature profiles along the horizontal structural tri-beam caps were evaluated for various orbital positions during the equinoxes and solstices. Figure 2-17 presents the expected variation in thermal gradients between primary and secondary structural caps. The average primary structure thermal gradient is approximately at the center of the antenna. The expected variation in this gradient is . The thermal gradients between secondary structural caps are small, , and do not present a significant thermally induced deflection environment. The vertical columns of the structure have the same view of the antenna surface and space, and consequently cannot be readily configured with coatings, insulation or geometry selection to minimize peak temperatures of the material. Figure 2-18 presents the maximum waste heat flux that will be experienced by the vertical columns for microwave converter efficiency of and . Eighty-seven percent of the waste heat generated by the converters is assumed radiated toward the structure. The parameter p is a scaling factor for the shape of the Gaussian distribution of microwave converters on the antenna surface. Limitations as to the taper of this distribution must be imposed depending upon the structural material selected. A near uniform distribution (1. 5 to 1) must be used if the structure is aluminum or graphite/epoxy (70% converter efficiency). Selection of graphite/polyimide would be compatible with a desirable 10:1 taper for the converter Gaussian distribution. 2. 2. 3. 2 Structural Analysis The Task 2 structural analysis objective was to refine the design of the structural members and to perform a detailed assessment of thermally induced deflections. The following summarizes these assessments: • The principal applied load for structure design is that induced by inertial response of the control system during breakaway from the slip-ring torque. This torque equates to a 100 lb (440N) end load on the upper and lower members.
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