History of GPS System, its Application and Future Directions

History of GPS System, its Application and Future Directions

• 1957 - The Soviet Union launches Sputnik. Scientists realise that due to the Doppler Effect, the frequency of the signal was higher as the satellite approached, and lower as it continued away from them. They realised that because they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion.

•1960 - The first satellite navigation system, TRANSIT, used by the US navy, was first successfully tested.

• 1967 - US navy developed the Timation satellite, which proved the ability to place accurate clocks in space, an ability upon which GPS relies.

• 1973 - development of the Navstar GPS begins

• 1978 - first experimental (prototype) block 1 GPS satellite was launched.

• 1983 - it is decided that once completed, the GPS will be available for civilian usage

• 1989 - first modern block II satellite launched.

• 1994 - complete constellation of 24 operational satellites was in orbit

• 1996 - U.S policy statement confirms duality of use i.e. military AND civillian

• 2005 - first IIR-M GPS satellite is launched. This new type of satellite supports the military "M" signal, and the 2nd civil signal L2C.

How it Works

• The GPS consists of 3 major segments: The Space Segment (or SV), control segment, and user segment.

• Space segment consists of 27 satellites, distributed equally along 6 orbital planes.

• The orbital planes have an approx. 55* inclination (tilt relative to the earths equator) and make 2 complete orbits every 24 hours.

• The orbits are arranged so at least 6 satellites are always within "line of sight" from almost everywhere on earth’s surface.

• The flight paths of the satellites are tracked by the CONTROL SEGMENT, which consists of several US air force monitoring stations across America.

• The control stations contact each GPS regularly with a navigational update, and to synchronize the atomic clocks on board to within a microsecond.

• The GPS receiver, or Use segment, is composed of an antenna tuned to the frequencies transmitted by the satellites, receiver-processors, which process the data transmitted, and a highly stable clock.

• A GPS receiver locates 3 or more of these sat. works out the distance to each, and then uses this info to deduce its own location based on the mathematical principle of spherical trilateration.

• Spherical trilateration: When you measure the distance to four located satellites, you can draw 4 spheres that all intersect at one point. That's where the receiver is. hurrah!

• The GPS receiver figures out the distance to and between each satellite by analysing high-frequency radio signals from the sat.

• The GPS sends out a pseudo-random code and the receiver receives it. the length of the delay is equal to the signal's travel time. the receiver multiplies this time by the speed of light to determine how far the signal travelled.

• GPS satellites broadcast 3 types of data in the primary navigation signal.

• The first is the almanac, which sense course time & status info about the sat.

• the 2nd is the ephemeris, which contains orbital information which allows the receiver to calculate the position of the satellite.

• Sat. transmit 2 carrier signals, the L1 frequency that carries the navigation message, and the L2 frequency which is used to measure ionosphere delay.

Applications

1. Automobile Navigation

The worldwide market for GPS in the automotive industry increase from just 2 million in 1997, to more than 11 million in 2001.

2. Fleet Tracking

Automatic Vehicle Location (AVL) is the combination of GPS and computer technology. Vehicles (planes, trains, trucks, cars, ships etc.) can be tracked, and identify the exact time and position of specific events i.e. deliveries, extended stops, etc.

3. Mapping & Surveying

GPS Surveying is the ideal way to survey positions in a short period of time. Each point surveyed is independent of the other, which eliminates time consuming traverse. With GPS, an unlimited area can be covered using satellite transmissions. One person is capable of conducting a field survey on foot or in a vehicle. Integrated with GIS systems, maps can be computer generated directly from the field survey data.

4. Mining

GPS gear linked to a computer-designed mine plan, increases efficiency up to 30%

5. Recreational uses

E.g. hunting and fishing, mountain biking, sailing and kayaking, hiking, car travel

6. Mobile phone GPS

7. Military

Missiles, submarines, aircraft

etc

Future Directions

• Interoperating with Europe’s GALILEO satellite navigation system