Satellite Technology – Principles and Applications 3e

Anil K. Maini Varsha Agrawal Laser Science and Technology Centre, Delhi, India

Preface xxi PART I SATELLITE TECHNOLOGY 1 Introduction to Satellites and their Applications 3 1.1 Ever-expanding Application Spectrum 3 1.2 What is a Satellite? 4 1.3 History of the Evolution of Satellites 7 1.3.1 Era of Hot Air Balloons and Sounding Rockets 7 1.3.2 Launch of Early Artificial Satellites 8 1.3.3 Satellites for Communications, Meteorology and Scientific Exploration -- Early Developments 10 1.3.4 Non-geosynchronous Communication Satellites: Telstar and Relay Programmes 11 1.3.5 Emergence of Geosynchronous Communication Satellites 12 1.3.6 International Communication Satellite Systems 15 1.3.7 Domestic Communication Satellite Systems 16 1.3.8 Satellites for other Applications also made Rapid Progress 19 1.3.9 Small or Miniature Satellites 22 1.4 Evolution of Launch Vehicles 27 1.5 Future Trends 33 1.5.1 Communication Satellites 33 1.5.2 Weather Forecasting Satellites 33 1.5.3 Earth Observation Satellites 33 1.5.4 Navigational Satellites 34 1.5.5 Military Satellites 35 Further Reading 35 Glossary 35 2 Satellite Orbits and Trajectories 37 2.1 Definition of an Orbit and a Trajectory 37 2.2 Orbiting Satellites -- Basic Principles 37 2.2.1 Newton s Law of Gravitation 39 2.2.2 Newton s Second Law of Motion 40 2.2.3 Kepler s Laws 41 2.3 Orbital Parameters 44 2.4 Injection Velocity and Resulting Satellite Trajectories 61 2.5 Types of Satellite Orbits 67 2.5.1 Orientation of the Orbital Plane 67 2.5.2 Eccentricity of the Orbit 68 2.5.3 Distance from Earth 70 2.5.4 Sun-synchronous Orbit 73 Further Readings 76 Glossary 76 3 Satellite Launch and In-orbit Operations 79 3.1 Acquiring the Desired Orbit 79 3.1.1 Parameters Defining the Satellite Orbit 80 3.1.2 Modifying the Orbital Parameters 83 3.2 Launch Sequence 95 3.2.1 Types of Launch Sequence 95 3.3 Launch Vehicles 100 3.3.1 Introduction 100 3.3.2 Classification 100 3.3.3 Anatomy of a Launch Vehicle 104 3.3.4 Principal Parameters 106 3.3.5 Major Launch Vehicles 108 3.4 Space Centres 127 3.4.1 Location Considerations 127 3.4.2 Constituent Parts of a Space Centre 128 3.4.3 Major Space Centres 129 3.5 Orbital Perturbations 144 3.6 Satellite Stabilization 146 3.6.1 Spin Stabilization 146 3.6.2 Three-axis or Body Stabilization 147 3.6.3 Comparison between Spin-stabilized and Three-axis Stabilized Satellites 149 3.6.4 Station Keeping 149 3.7 Orbital Effects on Satellite s Performance 149 3.7.1 Doppler Shift 149 3.7.2 Variation in the Orbital Distance 150 3.7.3 Solar Eclipse 150 3.7.4 Sun Transit Outrage 150 3.8 Eclipses 150 3.9 Look Angles of a Satellite 154 3.9.1 Azimuth Angle 154 3.9.2 Elevation Angle 155 3.9.3 Computing the Slant Range 156 3.9.4 Computing the Line-of-Sight Distance between Two Satellites 158 3.10 Earth Coverage and Ground Tracks 166 3.10.1 Satellite Altitude and the Earth Coverage Area 166 3.10.2 Satellite Ground Tracks 167 3.10.3 Orbit Inclination and Latitude Coverage 170 Further Readings 172 Glossary 172 4 Satellite Hardware 174 4.1 Satellite Subsystems 174 4.2 Mechanical Structure 175 4.2.1 Design Considerations 176 4.2.2 Typical Structure 176 4.3 Propulsion Subsystem 177 4.3.1 Basic Principle 178 4.3.2 Types of Propulsion System 178 4.4 Thermal Control Subsystem 185 4.4.1 Sources of Thermal Inequilibrium 186 4.4.2 Mechanism of Heat Transfer 186 4.4.3 Types of Thermal Control 187 4.5 Power Supply Subsystem 189 4.5.1 Types of Power System 189 4.5.2 Solar Energy Driven Power Systems 190 4.5.3 Batteries 195 4.6 Attitude and Orbit Control 199 4.6.1 Attitude Control 200 4.6.2 Orbit Control 200 4.7 Tracking, Telemetry and Command Subsystem 201 4.8 Payload 203 4.9 Antenna Subsystem 205 4.9.1 Antenna Parameters 207 4.9.2 Types of Antennas 210 4.10 Space Qualification and Equipment Reliability 224 4.10.1 Space Qualification 224 4.10.2 Reliability 225 Further Readings 226 Glossary 227 5 Communication Techniques 229 5.1 Types of Information Signals 229 5.1.1 Voice Signals 230 5.1.2 Data Signals 230 5.1.3 Video Signals 230 5.2 Amplitude Modulation 231 5.2.1 Frequency Spectrum of the AM Signal 232 5.2.2 Power in the AM Signal 233 5.2.3 Noise in the AM Signal 233 5.2.4 Different Forms of Amplitude Modulation 235 5.3 Frequency Modulation 241 5.3.1 Frequency Spectrum of the FM Signal 243 5.3.2 Narrow Band and Wide Band FM 245 5.3.3 Noise in the FM Signal 246 5.3.4 Generation of FM Signals 250 5.3.5 Detection of FM Signals 252 5.4 Pulse Communication Systems 259 5.4.1 Analogue Pulse Communication Systems 259 5.4.2 Digital Pulse Communication Systems 261 5.5 Sampling Theorem 265 5.6 Shannon--Hartley Theorem 266 5.7 Digital Modulation Techniques 267 5.7.1 Amplitude Shift Keying (ASK) 268 5.7.2 Frequency Shift Keying (FSK) 268 5.7.3 Phase Shift Keying (PSK) 269 5.7.4 Differential Phase Shift Keying (DPSK) 270 5.7.5 Quadrature Phase Shift Keying (QPSK) 271 5.7.6 Offset QPSK 273 5.7.7 8PSK and 16PSK 274 5.7.8 Quadrature Amplitude Modulation (QAM) 274 5.7.9 Amplitude Phase Shift Keying (APSK) 276 5.8 Multiplexing Techniques 277 5.8.1 Frequency Division Multiplexing 277 5.8.2 Time Division Multiplexing 279 5.8.3 Code Division Multiplexing 281 Further Readings 282 Glossary 283 6 Multiple Access Techniques 286 6.1 Introduction to Multiple Access Techniques 286 6.1.1 Transponder Assignment Modes 287 6.2 Frequency Division Multiple Access (FDMA) 288 6.2.1 Demand Assigned FDMA 290 6.2.2 Pre-assigned FDMA 290 6.2.3 Calculation of C/N Ratio 290 6.3 Single Channel Per Carrier (SCPC) Systems 293 6.3.1 SCPC/FM/FDMA System 293 6.3.2 SCPC/PSK/FDMA System 294 6.4 Multiple Channels Per Carrier (MCPC) Systems 295 6.4.1 MCPC/FDM/FM/FDMA System 295 6.4.2 MCPC/PCM-TDM/PSK/FDMA System 296 6.5 Time Division Multiple Access (TDMA) 297 6.6 TDMA Frame Structure 297 6.6.1 Reference Burst 298 6.6.2 Traffic Burst 298 6.6.3 Guard Time 299 6.7 TDMA Burst Structure 299 6.7.1 Carrier and Clock Recovery Sequence 299 6.7.2 Unique Word 299 6.7.3 Signalling Channel 300 6.7.4 Traffic Information 301 6.8 Computing Unique Word Detection Probability 301 6.9 TDMA Frame Efficiency 302 6.10 Control and Coordination of Traffic 303 6.11 Frame Acquisition and Synchronization 305 6.11.1 Extraction of Traffic Bursts from Receive Frames 305 6.11.2 Transmission of Traffic Bursts 305 6.11.3 Frame Synchronization 305 6.12 FDMA vs. TDMA 307 6.12.1 Advantages of TDMA over FDMA 308 6.12.2 Disadvantages of TDMA over FDMA 308 6.13 Code Division Multiple Access (CDMA) 308 6.13.1 DS-CDMA Transmission and Reception 309 6.13.2 Frequency Hopping CDMA (FH-CDMA) System 311 6.13.3 Time Hopping CDMA (TH-CDMA) System 313 6.13.4 Comparison of DS-CDMA, FH-CDMA and TH-CDMA Systems 314 6.14 Space Domain Multiple Access (SDMA) 316 6.14.1 Frequency Re-use in SDMA 316 6.14.2 SDMA/FDMA System 317 6.14.3 SDMA/TDMA System 318 6.14.4 SDMA/CDMA System 319 Further Readings 319 Glossary 320 7 Satellite Link Design Fundamentals 322 7.1 Transmission Equation 322 7.2 Satellite Link Parameters 324 7.2.1 Choice of Operating Frequency 324 7.2.2 Propagation Considerations 324 7.2.3 Noise Considerations 325 7.2.4 Interference-related Problems 325 7.3 Frequency Considerations 326 7.3.1 Frequency Allocation and Coordination 326 7.4 Propagation Considerations 330 7.4.1 Free-space Loss 330 7.4.2 Gaseous Absorption 331 7.4.3 Attenuation due to Rain 333 7.4.4 Cloud Attenuation 334 7.4.5 Signal Fading due to Refraction 334 7.4.6 Ionosphere-related Effects 335 7.4.7 Fading due to Multipath Signals 338 7.5 Techniques to Counter Propagation Effects 341 7.5.1 Attenuation Compensation Techniques 341 7.5.2 Depolarization Compensation Techniques 342 7.6 Noise Considerations 342 7.6.1 Thermal Noise 342 7.6.2 Noise Figure 343 7.6.3 Noise Temperature 344 7.6.4 Noise Figure and Noise Temperature of Cascaded Stages 345 7.6.5 Antenna Noise Temperature 346 7.6.6 Overall System Noise Temperature 350 7.7 Interference-related Problems 353 7.7.1 Intermodulation Distortion 354 7.7.2 Interference between the Satellite and Terrestrial Links 357 7.7.3 Interference due to Adjacent Satellites 357 7.7.4 Cross-polarization Interference 361 7.7.5 Adjacent Channel Interference 361 7.8 Antenna Gain-to-Noise Temperature (G/T) Ratio 365 7.9 Link Design 367 7.9.1 Link Design Procedure 368 7.9.2 Link Budget 368 7.10 Multiple Spot Beam Technology 371 Further Readings 374 Glossary 375 8 Earth Station 378 8.1 Earth Station 378 8.2 Types of Earth Station 380 8.2.1 Fixed Satellite Service (FSS) Earth Station 381 8.2.2 Broadcast Satellite Service (BSS) Earth Stations 382 8.2.3 Mobile Satellite Service (MSS) Earth Stations 383 8.2.4 Single Function Stations 384 8.2.5 Gateway Stations 385 8.2.6 Teleports 386 8.3 Earth Station Architecture 386 8.4 Earth Station Design Considerations 387 8.4.1 Key Performance Parameters 388 8.4.2 Earth Station Design Optimization 390 8.4.3 Environmental and Site Considerations 391 8.5 Earth Station Testing 392 8.5.1 Unit and Subsystem Level Testing 392 8.5.2 System Level Testing 392 8.6 Earth Station Hardware 398 8.6.1 RF Equipment 398 8.6.2 IF and Baseband Equipment 408 8.6.3 Terrestrial Interface 409 8.7 Satellite Tracking 412 8.7.1 Satellite Tracking System -- Block Diagram 412 8.7.2 Tracking Techniques 412 8.8 Some Representative Earth Stations 419 8.8.1 Goonhilly Satellite Earth Station 419 8.8.2 Madley Communications Centre 421 8.8.3 Madrid Deep Space Communications Complex 421 8.8.4 Canberra Deep Space Communications Complex 422 8.8.5 Goldstone Deep Space Communications Complex 423 8.8.6 Honeysuckle Creek Tracking Station 424 8.8.7 Kaena Point Satellite Tracking Station 426 8.8.8 Bukit Timah Satellite Earth Station 426 8.8.9 INTELSAT Teleport Earth Stations 426 8.8.10 SUPARCO Satellite Ground Station 428 8.8.11 Makarios Satellite Earth Station 428 8.8.12 Raisting Earth Station 428 8.8.13 Indian Deep Space Network 429 Glossary 430 9 Networking Concepts 433 9.1 Introduction 433 9.2 Network Characteristics 433 9.2.1 Availability 434 9.2.2 Reliability 434 9.2.3 Security 435 9.2.4 Throughput 436 9.2.5 Scalability 437 9.2.6 Topology 437 9.2.7 Cost 437 9.3 Applications and Services 437 9.3.1 Satellite and Network Services 438 9.3.2 Satellite Services 438 9.3.3 Network Services 438 9.3.4 Internet Services 439 9.4 Network Topologies 442 9.4.1 Bus Topology 442 9.4.2 Star Topology 443 9.4.3 Ring Topology 444 9.4.4 Mesh Topology 444 9.4.5 Tree Topology 445 9.4.6 Hybrid Topology 446 9.5 Network Technologies 447 9.5.1 Circuit Switched Networks 447 9.5.2 Packet Switched Networks 448 9.5.3 Circuit Switched versus Packet Switched Networks 449 9.6 Networking Protocols 450 9.6.1 Common Networking Protocols 450 9.6.2 The Open Systems Interconnect (OSI) Reference Model 453 9.6.3 Internet Protocol (IP) 456 9.6.4 Transmission Control Protocol (TCP) 457 9.6.5 Hyper Text Transfer Protocol (HTTP) 457 9.6.6 File Transfer Protocol (FTP) 457 9.6.7 Simple Mail Transfer Protocol (SMTP) 458 9.6.8 User Datagram Protocol (UDP) 458 9.6.9 Asynchronous Transfer Mode (ATM) 459 9.7 Satellite Constellations 459 9.7.1 Constellation Geometry 459 9.7.2 Major Satellite Constellations 460 9.8 Internetworking with Terrestrial Networks 465 9.8.1 Repeaters, Bridges, Switches and Routers 465 9.8.2 Protocol Translation, Stacking and Tunnelling 466 9.8.3 Quality of Service 466 Further Readings 467 Glossary 467 PART II SATELLITE APPLICATIONS 10 Communication Satellites 473 10.1 Introduction to Communication Satellites 473 10.2 Communication-related Applications of Satellites 474 10.2.1 Geostationary Satellite Communication Systems 475 10.2.2 Non-geostationary Satellite Communication Systems 475 10.3 Frequency Bands 475 10.4 Payloads 475 10.4.1 Types of Transponders 477 10.4.2 Transponder Performance Parameters 478 10.5 Satellite versus Terrestrial Networks 479 10.5.1 Advantages of Satellites Over Terrestrial Networks 479 10.5.2 Disadvantages of Satellites with Respect to Terrestrial Networks 480 10.6 Satellite Telephony 481 10.6.1 Point-to-Point Trunk Telephone Networks 482 10.6.2 Mobile Satellite Telephony 482 10.7 Satellite Television 484 10.7.1 A Typical Satellite TV Network 484 10.7.2 Satellite--Cable Television 485 10.7.3 Satellite--Local Broadcast TV Network 486 10.7.4 Direct-to-Home Satellite Television 487 10.7.5 Digital Video Broadcasting (DVB) 490 10.7.6 DVB-S and DVB-S2 Standards 491 10.7.7 DVB-RCS and DVB-RCS2 Standards 493 10.7.8 DVB-T and DVB-T2 Standards 493 10.7.9 DVB-H and DVB-SH Standards 494 10.8 Satellite Radio 496 10.9 Satellite Data Communication Services 496 10.9.1 Satellite Data Broadcasting 496 10.9.2 VSATs (Very Small Aperture Terminals) 497 10.10 Important Missions 502 10.10.1 International Satellite Systems 502 10.10.2 Regional Satellite Systems 512 10.10.3 National Satellite Systems 513 10.11 Future Trends 514 10.11.1 Development of Satellite Constellations in LEO Orbits 516 10.11.2 Development of Personal Communication Services (PCS) 516 10.11.3 Use of Higher Frequency Bands 517 10.11.4 Development of Light Quantum Communication Techniques 517 10.11.5 Development of Broadband Services to Mobile Users 517 10.11.6 Development of Hybrid Satellite/Terrestrial Networks 517 10.11.7 Advanced Concepts 518 Further Readings 519 Glossary 521 11 Remote Sensing Satellites 524 11.1 Remote Sensing -- An Overview 524 11.1.1 Aerial Remote Sensing 525 11.1.2 Satellite Remote Sensing 525 11.2 Classification of Satellite Remote Sensing Systems 526 11.2.1 Optical Remote Sensing Systems 526 11.2.2 Thermal Infrared Remote Sensing Systems 528 11.2.3 Microwave Remote Sensing Systems 529 11.3 Remote Sensing Satellite Orbits 531 11.4 Remote Sensing Satellite Payloads 531 11.4.1 Classification of Sensors 531 11.4.2 Sensor Parameters 534 11.5 Passive Sensors 535 11.5.1 Passive Scanning Sensors 536 11.5.2 Passive Non-scanning Sensors 539 11.6 Active Sensors 540 11.6.1 Active Non-scanning Sensors 540 11.6.2 Active Scanning Sensors 540 11.7 Types of Images 542 11.7.1 Primary Images 542 11.7.2 Secondary Images 542 11.8 Image Classification 545 11.9 Image Interpretation 546 11.9.1 Interpreting Optical and Thermal Remote Sensing Images 546 11.9.2 Interpreting Microwave Remote Sensing Images 547 11.9.3 GIS in Remote Sensing 547 11.10 Applications of Remote Sensing Satellites 548 11.10.1 Land Cover Classification 548 11.10.2 Land Cover Change Detection 549 11.10.3 Water Quality Monitoring and Management 550 11.10.4 Flood Monitoring 551 11.10.5 Urban Monitoring and Development 552 11.10.6 Measurement of Sea Surface Temperature 552 11.10.7 Deforestation 553 11.10.8 Global Monitoring 553 11.10.9 Predicting Disasters 555 11.10.10 Other Applications 558 11.11 Major Remote Sensing Missions 558 11.11.1 Landsat Satellite System 558 11.11.2 SPOT Satellite System 561 11.11.3 Radarsat Satellite System 564 11.11.4 Indian Remote Sensing Satellite System 565 11.12 Future Trends 573 Further Readings 574 Glossary 575 12 Weather Satellites 577 12.1 Weather Forecasting -- An Overview 577 12.2 Weather Forecasting Satellite Fundamentals 580 12.3 Images from Weather Forecasting Satellites 580 12.3.1 Visible Images 580 12.3.2 IR Images 582 12.3.3 Water Vapour Images 583 12.3.4 Microwave Images 584 12.3.5 Images Formed by Active Probing 585 12.4 Weather Forecasting Satellite Orbits 586 12.5 Weather Forecasting Satellite Payloads 587 12.5.1 Radiometer 588 12.5.2 Active Payloads 589 12.6 Image Processing and Analysis 592 12.6.1 Image Enhancement Techniques 592 12.7 Weather Forecasting Satellite Applications 593 12.7.1 Measurement of Cloud Parameters 594 12.7.2 Rainfall 594 12.7.3 Wind Speed and Direction 595 12.7.4 Ground-level Temperature Measurements 596 12.7.5 Air Pollution and Haze 596 12.7.6 Fog 596 12.7.7 Oceanography 596 12.7.8 Severe Storm Support 597 12.7.9 Fisheries 598 12.7.10 Snow and Ice Studies 598 12.8 Major Weather Forecasting Satellite Missions 599 12.8.1 GOES Satellite System 599 12.8.2 Meteosat Satellite System 605 12.8.3 Advanced TIROS-N (ATN) NOAA Satellites 608 12.9 Future of Weather Forecasting Satellite Systems 612 Further Readings 612 Glossary 613 13 Navigation Satellites 614 13.1 Development of Satellite Navigation Systems 614 13.1.1 Doppler Effect based Satellite Navigation Systems 615 13.1.2 Trilateration-based Satellite Navigation Systems 615 13.2 Global Positioning System (GPS) 621 13.2.1 Space Segment 621 13.2.2 Control Segment 622 13.2.3 User Segment 623 13.3 Working Principle of the GPS 625 13.3.1 Principle of Operation 625 13.3.2 GPS Signal Structure 627 13.3.3 Pseudorange Measurements 628 13.3.4 Determination of the Receiver Location 629 13.4 GPS Positioning Services and Positioning Modes 631 13.4.1 GPS Positioning Services 631 13.4.2 GPS Positioning Modes 632 13.5 GPS Error Sources 634 13.6 GLONASS Satellite System 637 13.6.1 GLONASS Segments 638 13.6.2 GLONASS Signal Structure 639 13.7 GPS-GLONASS Integration 641 13.8 EGNOS Satellite Navigation System 642 13.9 Galileo Satellite Navigation Systems 645 13.9.1 Three-Phase Development Programme 645 13.9.2 Services 646 13.10 Indian Regional Navigational Satellite System (IRNSS) 647 13.11 Compass Satellite Navigation System 648 13.12 Hybrid Navigation Systems 648 13.13 Applications of Satellite Navigation Systems 650 13.13.1 Military Applications 650 13.13.2 Civilian Applications 651 13.14 Future of Satellite Navigation Systems 654 Further Readings 655 Glossary 656 14 Scientific Satellites 658 14.1 Satellite-based versus Ground-based Scientific Techniques 658 14.2 Payloads on Board Scientific Satellites 659 14.2.1 Payloads for Studying Earth s Geodesy 659 14.2.2 Payloads for Earth Environment Studies 660 14.2.3 Payloads for Astronomical Studies 661 14.3 Applications of Scientific Satellites -- Study of Earth 665 14.3.1 Space Geodesy 665 14.3.2 Tectonics and Internal Geodynamics 669 14.3.3 Terrestrial Magnetic Fields 670 14.4 Observation of the Earth s Environment 670 14.4.1 Study of the Earth s Ionosphere and Magnetosphere 671 14.4.2 Study of the Earth s Upper Atmosphere (Aeronomy) 677 14.4.3 Study of the Interaction between Earth and its Environment 679 14.5 Astronomical Observations 680 14.5.1 Observation of the Sun 681 14.6 Missions for Studying Planets of the Solar System 686 14.6.1 Mercury 691 14.6.2 Venus 692 14.6.3 Mars 694 14.6.4 Outer Planets 697 14.6.5 Moon 703 14.6.6 Asteroids 705 14.6.7 Comets 706 14.7 Missions Beyond the Solar System 707 14.8 Other Fields of Investigation 710 14.8.1 Microgravity Experiments 710 14.8.2 Life Sciences 711 14.8.3 Material Sciences 712 14.8.4 Cosmic Ray and Fundamental Physics Research 713 14.9 Future Trends 714 Further Readings 715 Glossary 715 15 Military Satellites 717 15.1 Military Satellites -- An Overview 717 15.1.1 Applications of Military Satellites 718 15.2 Military Communication Satellites 718 15.3 Development of Military Communication Satellite Systems 719 15.3.1 American Systems 720 15.3.2 Russian Systems 724 15.3.3 Satellites Launched by other Countries 725 15.4 Frequency Spectrum Utilized by Military Communication Satellite Systems 726 15.5 Dual-use Military Communication Satellite Systems 727 15.6 Reconnaisance Satellites 728 15.6.1 Image Intelligence or IMINT Satellites 728 15.7 SIGINT Satellites 732 15.7.1 Development of SIGINT Satellites 733 15.8 Early Warning Satellites 735 15.8.1 Major Early Warning Satellite Programmes 736 15.9 Nuclear Explosion Satellites 738 15.10 Military Weather Forecasting Satellites 738 15.11 Military Navigation Satellites 739 15.12 Space Weapons 739 15.12.1 Classification of Space Weapons 740 15.13 Strategic Defence Initiative 745 15.13.1 Ground Based Programmes 746 15.13.2 Directed Energy Weapon Programmes 749 15.13.3 Space Programmes 751 15.13.4 Sensor Programmes 752 15.14 Directed Energy Laser Weapons 752 15.14.1 Advantages 753 15.14.2 Limitations 753 15.14.3 Directed Energy Laser Weapon Components 754 15.14.4 Important Design Parametres 755 15.14.5 Important Laser Sources 756 15.14.6 Beam Control Technology 763 15.15 Advanced Concepts 764 15.15.1 New Surveillance Concepts Using Satellites 765 15.15.2 Long Reach Non-lethal Laser Dazzler 765 15.15.3 Long Reach Laser Target Designator 766 Further Readings 767 Glossary 767 16 Emerging Trends 769 16.1 Introduction 769 16.2 Space Tethers 769 16.2.1 Space Tethers -- Different Types 770 16.2.2 Applications 774 16.2.3 Space Tether Missions 775 16.2.4 Space Elevator 779 16.3 Aerostat Systems 781 16.3.1 Components of an Aerostat System 782 16.3.2 Types of Aerostat Systems 782 16.3.3 Applications 783 16.4 Millimetre Wave Satellite Communication 784 16.4.1 Millimetre Wave Band 784 16.4.2 Advantages 785 16.4.3 Propagation Considerations 787 16.4.4 Applications 788 16.4.5 Millimetre Wave Satellite Missions 789 16.5 Space Stations 793 16.5.1 Importance of Space Stations 794 16.5.2 Space Stations of the Past 794 16.5.3 Currently Operational Systems 797 16.5.4 Planned Space Stations 799 16.5.5 Emerging Space Station Concepts 801 Further Readings 803 Glossary 804 Index 807