EVOLUTION OF GLOBAL POSITIONING SYSTEM (GPS)

Evolution of Global Positioning System (GPS)

Evolution of Global Positioning System (GPS)

GPS is a satellite based system that was designed by the US Department of Defense to "simplify and improve military and civilian navigation and positioning anywhere on earth." There are three components to the system: the space component, the control component, and the user component. Looking first at the space component, there are 24 satellites orbiting approximately 10,900 nautical miles above the earth. These satellites travel along one of six orbital planes, with each one making a complete orbit in slightly less than 12 hours.

All the while, these satellites are sending streams of radio signals to Earth that contain information on their orbit, the condition/status of the satellite, and importantly, the exact time as determined by their onboard atomic clocks. The reliability and accuracy of the entire GPS rests on the accuracy of the clock, but given that the atomic clock is known to only lose or gain one second every 6 million years, it is safe to say that there is no need to worry about a loss of synchronization, at least in our lifetimes. In any case, scientists are constantly working to improve the efficiency of the clock. The orbit that the satellites can clearly be seen in the illustration to the left.

The second component is that of control. There are five monitoring stations located throughout the world, with the master control station (MCS) located at the Falcon Air Force Base in Colorado. From the MCS, information is processed and then sent to other monitoring stations "where satellite clock and orbital corrections can be made via ground antennas." The final component, and by far the most familiar to the typical layman, is the user device.

This can assume many shapes and forms, but is generally a receiver that processes the information being sent by the satellites and allows the user to determine his position and velocity. "Equipped with a GPS receiver, it is possible to navigate or collect positions while stationary or moving and while located on the ground, in the air or over water." In sum, the way that the whole system works can be described as follows:

GPS determines location by computing the difference between the time that a signal is sent and the time it is received. GPS satellites carry atomic clocks that provide extremely accurate time. The time information is placed in the codes broadcast by the satellite. Receivers on the earth's surface use the time difference between the time of signal reception and the broadcast time to compute the distance, or range, from the receiver to the satellite. By taking a measurement from four satellites, the receiver can compute latitude, longitude, altitude, and time.

The Development of the Global Positioning System

Though its availability to the mass public is an event of recent history, the development of the GPS goes back to 1938. In that year, Rabi, a professor at Columbia University, invented molecular-beam magnetic resonance, which ultimately became an integral ...