Introduction to the Global Positioning System An AAPT/PTRA Workshop Fred Nelson Manhattan High School

What is the GPS? Orbiting navigational satellites Orbiting navigational satellites Transmit position and time data Transmit position and time data Handheld receivers calculate Handheld receivers calculate latitude latitude longitude longitude altitude altitude velocity velocity Developed by Department of Defense Developed by Department of Defense

History of the GPS 1969—Defense Navigation Satellite System (DNSS) formed 1969—Defense Navigation Satellite System (DNSS) formed 1973—NAVSTAR Global Positioning System developed 1973—NAVSTAR Global Positioning System developed 1978—first 4 satellites launched 1978—first 4 satellites launched Delta rocket launch

History of the GPS 1993—24th satellite launched; initial operational capability 1993—24th satellite launched; initial operational capability 1995—full operational capability 1995—full operational capability May 2000—Military accuracy available to all users May 2000—Military accuracy available to all users

Components of the System Space segment 24 satellite vehicles 24 satellite vehicles Six orbital planes Six orbital planes Inclined 55 o with respect to equator Inclined 55 o with respect to equator Orbits separated by 60 o Orbits separated by 60 o 20,200 km elevation above Earth 20,200 km elevation above Earth Orbital period of 11 hr 55 min Orbital period of 11 hr 55 min Five to eight satellites visible from any point on Earth Five to eight satellites visible from any point on Earth Block I Satellite Vehicle

The GPS Constellation

GPS Satellite Vehicle Four atomic clocks Four atomic clocks Three nickel-cadmium batteries Three nickel-cadmium batteries Two solar panels Two solar panels Battery charging Power generation 1136 watts S band antenna—satellite control S band antenna—satellite control 12 element L band antenna— user communication 12 element L band antenna— user communication Block IIF satellite vehicle (fourth generation)

GPS Satellite Vehicle Weight Weight 2370 pounds 2370 pounds Height Height feet feet Width Width feet including wing span feet including wing span Design life—10 years Design life—10 years Block IIR satellite vehicle assembly at Lockheed Martin, Valley Forge, PA

Components of the System User segment GPS antennas & receiver/processors GPS antennas & receiver/processors Position Position Velocity Velocity Precise timing Precise timing Used by Used by Aircraft Aircraft Ground vehicles Ground vehicles Ships Ships Individuals Individuals

Components of the System Ground control segment Master control station Master control station Schreiver AFB, Colorado Schreiver AFB, Colorado Five monitor stations Five monitor stations Three ground antennas Three ground antennas Backup control system Backup control system

GPS Communication and Control

GPS Ground Control Stations

How does GPS work? Satellite ranging Satellite ranging Satellite locations Satellite locations Satellite to user distance Satellite to user distance Need four satellites to determine position Need four satellites to determine position Distance measurement Distance measurement Radio signal traveling at speed of light Radio signal traveling at speed of light Measure time from satellite to user Measure time from satellite to user Low-tech simulation Low-tech simulation

How does GPS work? Pseudo-Random Code Complex signal Complex signal Unique to each satellite Unique to each satellite All satellites use same frequency All satellites use same frequency “Amplified” by information theory “Amplified” by information theory information theory information theory Economical Economical

How does GPS work? Distance to a satellite is determined by measuring how long a radio signal takes to reach us from that satellite. Distance to a satellite is determined by measuring how long a radio signal takes to reach us from that satellite. To make the measurement we assume that both the satellite and our receiver are generating the same pseudo-random codes at exactly the same time. To make the measurement we assume that both the satellite and our receiver are generating the same pseudo-random codes at exactly the same time. By comparing how late the satellite's pseudo-random code appears compared to our receiver's code, we determine how long it took to reach us. By comparing how late the satellite's pseudo-random code appears compared to our receiver's code, we determine how long it took to reach us. Multiply that travel time by the speed of light and you've got distance. Multiply that travel time by the speed of light and you've got distance. High-tech simulation High-tech simulation High-tech simulation High-tech simulation

How does GPS work? Accurate timing is the key to measuring distance to satellites. Accurate timing is the key to measuring distance to satellites. Satellites are accurate because they have four atomic clocks ($100,000 each) on board. Satellites are accurate because they have four atomic clocks ($100,000 each) on board. Receiver clocks don't have to be too accurate because an extra satellite range measurement can remove errors. Receiver clocks don't have to be too accurate because an extra satellite range measurement can remove errors.

How does GPS work? To use the satellites as references for range measurements we need to know exactly where they are. To use the satellites as references for range measurements we need to know exactly where they are. GPS satellites are so high up their orbits are very predictable. GPS satellites are so high up their orbits are very predictable. All GPS receivers have an almanac programmed into their computers that tells them where in the sky each satellite is, moment by moment. All GPS receivers have an almanac programmed into their computers that tells them where in the sky each satellite is, moment by moment. Minor variations in their orbits are measured by the Department of Defense. Minor variations in their orbits are measured by the Department of Defense. The error information is sent to the satellites, to be transmitted along with the timing signals. The error information is sent to the satellites, to be transmitted along with the timing signals.

GPS Position Determination

System Performance Standard Positioning System Standard Positioning System 100 meters horizontal accuracy 156 meters vertical accuracy Designed for civilian use No user fee or restrictions Precise Positioning System Precise Positioning System 22 meters horizontal accuracy 27.7 meters vertical accuracy Designed for military use

System Performance Selective availability Intentional degradation of signal Intentional degradation of signal Controls availability of system’s full capabilities Controls availability of system’s full capabilities Set to zero May 2000 Set to zero May 2000 Reasons Reasons Enhanced 911 service Enhanced 911 service Car navigation Car navigation Adoption of GPS time standard Adoption of GPS time standard Recreation Recreation

System Performance The earth's ionosphere and atmosphere cause delays in the GPS signal that translate into position errors. The earth's ionosphere and atmosphere cause delays in the GPS signal that translate into position errors. Some errors can be factored out using mathematics and modeling. Some errors can be factored out using mathematics and modeling. The configuration of the satellites in the sky can magnify other errors. The configuration of the satellites in the sky can magnify other errors. Differential GPS can reduce errors. Differential GPS can reduce errors. Differential GPS Differential GPS

Application of GPS Technology Location - determining a basic position Location - determining a basic position Navigation - getting from one location to another Navigation - getting from one location to another Tracking - monitoring the movement of people and things Tracking - monitoring the movement of people and things Mapping - creating maps of the world Mapping - creating maps of the world Timing - bringing precise timing to the world Timing - bringing precise timing to the world

Application of GPS Technology Private and recreation Private and recreation Traveling by car Traveling by car Hiking, climbing, biking Hiking, climbing, biking Vehicle control Vehicle control Mapping, survey, geology Mapping, survey, geology English Channel Tunnel English Channel Tunnel Agriculture Agriculture Agriculture Aviation Aviation General and commercial General and commercial Spacecraft Spacecraft Maritime Maritime

GPS Navigation

GPS News news.htm news.htm news.htm news.htm One–page reading exercise One–page reading exercise Center of page—main topic Center of page—main topic Four corners—questions & answers from reading Four corners—questions & answers from reading Four sides—specific facts from reading Four sides—specific facts from reading Spaces between—supporting ideas, diagrams, definitions Spaces between—supporting ideas, diagrams, definitions Article citation on back of page Article citation on back of page

Military Uses for the GPS Operation Desert Storm Featureless terrain Featureless terrain Initial purchase of 1000 portable commercial receivers Initial purchase of 1000 portable commercial receivers More than 9000 receivers in use by end of the conflict More than 9000 receivers in use by end of the conflict Foot soldiers Foot soldiers Vehicles Vehicles Aircraft Aircraft Marine vessels Marine vessels

Geocaching Cache of goodies established by individuals Cache of goodies established by individuals Coordinates published on Web Coordinates published on Web Find cache Find cache Leave a message Leave some treasure Take some treasure

Handheld GPS Receivers Garmin eTrex Garmin eTrex ~$100 ~$100 Garmin-12 Garmin-12 ~$150 ~$150 Casio GPS wristwatch Casio GPS wristwatch ~$300 ~$300 The GPS Store The GPS Store The GPS Store The GPS Store

GPS Operation Jargon “Waypoint” or “Landmark” “Waypoint” or “Landmark” “Track” or “Heading” “Track” or “Heading” “Bearing” “Bearing” CDI CDI Route Route Mark Mark GOTO GOTO GPS/Digital Telephone

GPS Websites USNO NAVSTAR Homepage USNO NAVSTAR Homepage USNO NAVSTAR Homepage USNO NAVSTAR Homepage Info on the GPS constellation How Stuff Works GPS How Stuff Works GPS How Stuff Works GPS How Stuff Works GPS Good everyday language explanation Trimble GPS tutorial Trimble GPS tutorial Trimble GPS tutorial Trimble GPS tutorial Flash animations GPS Waypoint registry GPS Waypoint registry GPS Waypoint registry GPS Waypoint registry Database of coordinates

Classroom Applications Physics Physics Distance, velocity, time Distance, velocity, time Orbital concepts Orbital concepts Earth Science Earth Science Mapping Mapping Spacecraft Spacecraft Environmental Science Environmental Science Migratory patterns Migratory patterns Population distributions Population distributions GLOBE Program GLOBE Program GLOBE Program GLOBE Program Mathematics Mathematics Mathematics Geography Geography Geography Technology Technology

Classroom Applications Careers Aerospace Aerospace Satellite vehicles Satellite vehicles Launch vehicles Launch vehicles Hardware engineering Hardware engineering Ground control systems Ground control systems User systems User systems Software engineering Software engineering Research careers Research careers

In and Out of the Classroom

Problem Solving

Sometimes the solution is over your head...

Kansas Science Education Standards Students will: demonstrate the fundamental abilities necessary to do scientific inquiry demonstrate the fundamental abilities necessary to do scientific inquiry apply different kinds of investigations to different kinds of questions apply different kinds of investigations to different kinds of questions expand their use and understanding of science and technology expand their use and understanding of science and technology

National Science Education Teaching Standards Standards Teachers of science Teachers of science Plan an inquiry-based science program for their students Plan an inquiry-based science program for their students Guide and facilitate learning Guide and facilitate learning Design and manage learning environments that provide students with the time, space, and resources needed for learning science Design and manage learning environments that provide students with the time, space, and resources needed for learning science

National Science Education Content Standards. all students should develop. all students should develop Abilities necessary to do scientific inquiry Abilities necessary to do scientific inquiry Understandings about scientific inquiry Understandings about scientific inquiry Abilities of technological design Abilities of technological design Understandings about science and technology Understandings about science and technology Understandings about Understandings about Motions and forces Motions and forces Population growth Population growth Natural resources Natural resources Environmental quality Environmental quality Science and technology in local, national, and global challenges Science and technology in local, national, and global challenges

“Where does he get those wonderful toys?” Student-centered Student-centered High interest High interest Outdoors Outdoors High visibility High visibility Integrated curriculum Integrated curriculum Inquiry Inquiry

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