Global Positioning System

1. Global Positioning System

2. What is GPS? • A worldwide radio-navigation system • constellation of 24 satellites • with 5 ground stations • GPS uses these “man-made stars” (statellites) as: • reference points for locations on earth • to calculate positions • accurate to a matter of meters

3. Common Man’s Utility • GPS receivers: • miniaturized with a few integrated circuits • thus becoming very economical • Making this technology accessible • to all • GPS is in: • cars, boats, planes, laptops, cell phones • construction equipment • movie making gear, farm machinery

4. Navigation • Mankind has always needed a way to: • calculate where he is on the earth • calculate where he is going • Old ways included • “dead reckoning”, landmarks, • observing the sun, moon, and stars • Who wants to be lost: • at sea, in the desert, in the cold or heat, • in a war zone, • or just out hiking?

5. Who Developed GPS? • U.S. Department of Defense • spent $12 billion • creating precise form of worldwide positioning • When/why • in the late days of the arms race • ability to take out Russia’s missile system • Result: • profoundly affected the balance of power

6. Land vs. Sea • Russia’s nuclear system was on land • U.S. nuclear arsenal largely at sea • on submarines • For precise targeting, • must have accurate launching coordinates • as well as precise target coordinates • A submarine must • surface and • accurately fix its exact position • within minutes anywhere in the world

7. How Does GPS Work? • The basis of GPS is “triangulation” • To triangulate: • GPS receiver measures distance from satellites • uses the travel time of radio signals • from 3 or more satellites • To measure travel time, GPS needs: • very accurate timing • location of/distance of satellites • corrections for delays as signal travels through the atmosphere

8. Disturbances in Signals • The ionosphere • has ionized particles (+atoms) • exert a perturbing effect on signals • The troposphere • is full of water vapor, • variances in temperature & atmospheric pressure • these also disturb the GPS signals

9. GPS Master Plan • Launch of the 24th block II satellite • in March 1994 • completed the GPS constellation • Four additional satellites • in reserve to be launched “on need” • Spacing of satellites • minimum of five satellites are in view • from every point on the globe

10. GPS Constellation

11. Satellites (Example) • Name: NAVSTAR • Manufacturer: Rockwell International • Altitude: 10,900 nautical miles • Size: 17 ft. with solar panels extended • Orbital Period: 12 hours • Orbital Plane: 55 degrees to equatorial plane • Lifespan: 7.5 years • Current constellation: 24 Block II production satellites

12. NAVSTAR Satellite

13. Ground Stations • Also known as the Control Segments • Checks both the: • operational health and • exact position of satellite in space • Transmit corrections • Five monitoring stations: • Hawaii, Ascension Island, Diego Garcia, • Kwajalein, and Colorado Springs

14. Land Control Segments

15. Websites • http://web.haystack.mit.edu/pcr/whereami/documents/gpstutorial.htm • http://www.trimble.com/gps/index.html • http://science.nasa.gov/Realtime/jtrack/3d/JTrack3D.html

16. Interest • What ways can you think of using GPS in our daily lives • What is the future of GPS • What careers would be related?