The Navstar Global Positioning System

Duringthe PersianGulfWaragroupofAmericansoldiersscoopedup anew recruitatRijaid Airport, thendrovehim,withblackenedheadlights, directly across miles oftractless desertsand.Squintingtoward the horizon, hecould see almost nothing when suddenly the driver mashed on the brakes, gave him a quick salute, and instructed him to step out into the darkness. As his bootssankintothesand,hewasstunned torealizethathewasonlyafew feet away from the flap of his tent. Before setting out, the driver had keyed the tent'scoordinates into a Navstar receiver, so itcould guide him back again. No one knows exactly how many Navstar receivers ended up serving coalition forces along the Persian Gulf because mothers and fathers-and sweethearts, too-located a few stray units on the shelves of marinesupply houses/plunked down their money, and express mailed them to their loved ones in the Persian Gulf. A few resourceful soldiers called stateside suppliers long distance, then used their credit cards to order receivers, many of which arrived in Saudi Arabiaa dayortwolateraboardcommercialjetliners. Bythe timetheground war finally started, 4,000 to 7,000 Navstar receivers were clutched in the hands of grateful American soldiers. They were used to guide fuel-starved airplanes for linkups with aerial tankers, to pull in air strikes against enemy emplacements, to guide mess trucks toward hungry troops, and to vector Special Forcesunits intheir muffled dune buggies deep behindenemylines. Afew enterprising military engineers learned how to follow meandering goat trails so they could locate underground springs where the goats wa- tered themselves. They then used their hand-held Navstar receivers to record the precise coordinates of each spring, thus insuring fresh water supplies for onrushing troops.

1 The Science of Navigation.- What Is Navigation?.- A Typical Ground-Based Radionavigation System.- The Advantages of Space-based Transmitters.- The Transit Navigation Satellites.- Gravity Gradient Stabilization.- Disturbance Compensation Systems.- Compensating for Ionospheric Delays.- Compensating for Tropospheric Delays.- Navigation Techniques.- The Navstar Revolution.- Navstar Navigation Techniques.- The Navstar Clocks.- Practical Benefits for All Mankind.- 2 The Navstar GPS.- The Space Segment.- Signal Structure and Pseudorandom Codes.- Navigation Solutions.- Correcting for Relativistic Time Delays.- Correcting for Ionospheric and Tropospheric Delays.- Decoding the 50-Bit-Per-Second Data Stream.- The Various Families of Navstar Satellites.- The User Segment.- A Typical High-Performance 5-Channel Receiver.- Operating Procedures.- The Control Segment.- Inverting the Navigation Solution.- The Monitor Stations and The Master Control Station.- Field Test Results.- 3 Performance Comparisons for Today’s Radionavigation Systems.- A Sampling of Today’s Ground-based Navigation Systems.- Loran C/D.- Omega.- VOR/DME Tacan.- The Microwave Landing System.- Inertial Navigation.- JTIDS Relnav and PLRS.- Signpost Navigation Techniques.- A Sampling of Today’s Space-based Navigation Systems.- Transit.- The Navstar Global Positioning System.- The French Argos.- Side-by-side Performance Comparisons.- 4 User-Set Architecture.- The Major Components of a Typical Navstar Receiver.- The Receiver Antenna and Its Associated Electronics.- The Tracking Loops.- Navigation Processor.- Power Supply.- Control-Display Unit.- Choosing the Proper User-set Architecture.- Performance Comparisons.- Selecting the Antennas.- Selecting the Proper Computer Processing Techniques.- Solving for the User’s Position.- Computing and Interpreting the Geometrical Dilution of Precision.- Ranging Error Budgets.- Kalman Filtering Techniques.- 5 User-set Performance.- Accuracy Estimates for Various Methods of Navigation.- Performance Criteria to Consider when Purchasing a Navstar Receiver.- Receiver Design Choices.- Number of Channels and Sequencing Rate.- Access to Selective-availability Signals.- Available Performance Enhancement Techniques.- Computer Processing Capabilities.- Receiver Design Smart Card.- Today’s Available Navstar Receivers.- Hand-held Receivers.- Commercially Available Navstar Chipsets.- 6 Differential Navigation and Pseudo-satellites.- Performance Comparisons: Absolute and Differential Navigation.- Special Committee 104’s Recommended Data-exchange Protocols.- The Coast Guard’s Differential Navigation System Tests.- Motorola’s Mini Ranger Test Results.- COMSAT’s Data Distribution Service for the Gulf of Mexico.- Wide-area Differential Navigation Services.- Pseudo-satellites.- Special Committee 104’s Data Exchange Protocols for Pseudo-satellites.- Comparisons Between Differential Navigation and Pseudo-satellites.- 7 Interferometry Techniques.- The Classical Michaelson-Morley Interferometry Experiment.- Measuring Attitude Angles with Special Navstar Receivers.- Eliminating Solution Ambiguities.- Practical Test Results.- Using Interferometry to Fix Position.- Single, Double, and Triple Differencing Techniques.- The POPS Post-Processing Software.- Spaceborne Interferometry Receivers.- Motorola’s Commercially Available Monarch.- Tomorrow’s Generic Spaceborne Receivers.- 8 Integrated Navigation Systems.- Integrated Navigation.- Inertial Navigation.- Error Growth Rates.- Reinitialization Techniques.- Ring Laser Gyros.- Monolithic Ring Laser Gyros.- Fiber Optic Gyros.- Using the GPS for Testing Inertial Navigation Systems.- The Practical Benefits of Integrated Navigation.- Chassis-level Integration.- 9 Interoperability with Other Navigation Systems.- The Soviet Glonass.- The Glonass Specification Release at Montreal.- The Glonass Constellation.- Orbital Maneuvers for the Glonass Satellites.- Building Dual-capability GPS/Glonass Receivers.- Receiver Design Difficulties.- Dual-Capability Receiver Tests at Leeds University.- The FAA’s Joint Research Efforts with Soviet Scientists.- Other Attempts to Build Dual-capability Receivers.- Integrity Monitoring Techniques.- Interoperability with Other Radionavigation Systems.- Eastport International’s Integrated System for Underwater Navigation.- 10 The Navstar Satellites.- The Eight Major Spacecraft Subsystems.- The Orbit Injection Subsystem.- Tracking, Telemetry and Command.- Attitude and Velocity Control.- Electrical Power.- Navigation Subsystem.- Reaction Control.- Thermal Control.- Structures and Mechanisms.- On-orbit Test Results.- The Multiyear Spacecraft Procurement.- Booster Rockets.- Orbital Perturbations.- The Spacecraft Ephemeris Constants.- Satellite Viewing Angles.- Earth-shadowing Intervals.- Repeating Ground-trace Geometry.- 11 Precise Time Synchronization.- John Harrison’s Marine Chronometer.- Celestial Navigation Techniques.- A Short History of Time.- The Atomic Clocks Carried Aboard the Navstar Satellites.- Cesium Atomic Clocks.- Rubidium Atomic Clocks.- Developing Atomic Clocks Light Enough to Travel Into Space.- The Growing Need for Precise Time Synchronization.- Time Sync Methodologies.- Fixing Time with the Navstar Signals.- Lightweight Hydrogen Masers for Tomorrow’s Navstar Satellites.- Crosslink Ranging Techniques.- 12 Digital Avionics and Air Traffic Control.- The Sabreliner’s Flight to the Paris Air Show.- Four Major Concerns of the Federal Aviation Administration.- Selective Availability.- User-Set Fees.- Integrity-related Failures.- Continuous Five-satellite Coverage.- Using a Dedicated Constellation for Air Traffic Control.- An Alternative Architecture Using the GPS.- Comparisons Between Geosynchronous and Semisynchronous Constellations.- Piggyback Geosynchronous Payloads.- The Autoland System Test Results.- 13 Geodetic Surveying and Satellite Positioning.- Determining the Shape of Planet Earth.- The Theory of Isostasy.- The Earth’s Contours Under Hydrostatic Equilibrium.- GPS Calibrations at the Turtmann Test Range.- Static Surveying Techniques.- Kinematic and Pseudo-kinematic Surveying.- Freeway Surveying During War in the Persian Gulf.- Navstar Positioning for Landsat D.- The Landsat’s Spaceborne Receiver.- On-Orbit Navigation Accuracy.- Orbit Determination for High-altitude Satellites.- Today’s Available Spaceborne Receivers.- 14 Military Applications.- The Military Benefits of the Worldwide Common Grid.- Field Test Results.- Projected Battlefield Benefits.- Test Range Applications.- Military Receivers.- Carrier-landing Accuracies.- Amphibious Warfare Operations.- Accuracy-enhancements for Strategic and Cruise Missiles.- 15 Civil Applications.- Dinosaur Hunting with the GPS.- Guiding Archaeological Expeditions.- Tracking Hazardous Icebergs.- Offshore Oil Exploration.- Fixing the Positions of Railroad Trains.- Automobile Navigation.- Dead Reckoning Systems.- Tomorrow’s Space-based Vehicle Navigation Techniques.- Today’s Available Automotive Navigation Systems.- Futuristic Applications for Navstar Navigation.- Appendix A Additional Sources of lnformation.- GPS Information Centers.- The U.S. Coast Guard’s Information Center.- The Computer Bulletin Board at Holloman Air Force Base.- Global Satellite Software’s Computer Bulletin Board.- The Glonass Computer Bulletin Board.- Precise GPS Orbit Information.- Military GPS Information Directory.- GPS Information with a European Flavor.- The United Kingdom.- The Netherlands.- Norway.- GPS Clock Behavior.- Information for Surveyors.- GPS World Magazine.- The Federal Radionavigation Plan.- Appendix B Today’s Global Family of User-set Makers.- Domestic User-set Makers.- Foreign User-set Makers.- Appendix C Navigation-Related Clubs and Organizations.- Appendix D Navigation-related Magazines and Periodicals.