The art and science of navigation has been around for thousands of years. The earliest navigators used the earth's magnetic field and the positions of the sun, moon and stars in the sky to guide them on their journeys. In fact, many sailors today still use the celestial navigation methods of centuries ago. Using charts of the positions of various celestial objects at different times of the year, directions can be accurately determined. Dr. Don Drost, a physicist presently in charge of the SCI 100 course, taught a very popular celestial navigation course at UVI about five years ago. (If sufficient interest is shown, perhaps he could be persuaded to teach it again!)
Flight
Airline pilots use a combination of systems. A compass gives a rather rough direction of flight, the altimeter (along with local weather information on barometric pressure) gives altitude, and a gyroscope yields information on the pitch and yaw of the aircraft. But this is insufficient to safely pilot a plane over large distances, during night or during days of low visibility. The primary systems that guide commercial airlines are the inertial navigation system and the radio navigation systems (such as VOR and TACAN). The Aerospace Corporation has a history of navigation site that provides a description of these navigational methods use by aircraft.
Near an airport, it is the controllers that do the navigating. Using radar to track the position of every aircraft in the vicinity, they radio the pilots with precise instructions concerning altitude, bearing and speed. These instructions are referred to as "vectors", but technically they are not. In addition to direction, a displacement magnitude could be specified, but that is not a practical method for the controllers. For those who are interested, details of the art of flight navigation can be found at Ed Williams navigation site.
GPS
But another system, incredibly precise, convenient, and increasingly economical, has transformed navigation. It is presently being used by such diverse interests as commercial airlines to land surveyors. Work is in progress to produce an affordable version for your car. It is the Global Positioning System.
Global Positioning System (GPS) is an international system of global location using satellites in orbit about the earth in conjunction with ground based stations. The user of the GPS system must have a GPS receiver. This device (UVI's Science Division has several economical hand held models) communicates with the satellites which in turn are in contact with the ground stations. The GPS receiver uses the signals of three or more satellites to pinpoint its location on earth. By knowing the precise position of the satellites (the ground stations help monitor position) and the time required for the signal to travel from the satellite to the receiver (typically < 1/10 of a second), the receiver can determine its position. Most receivers are accurate to within several meters, but the new differential receivers are capable of accuracy within centimeters!
Gemini Positioning Systems is a company that makes GPS electronic equipment. They have a very nice
GPS tutorial that will lead you through the basics. The Trimble company has a more extensive How GPS Works tutorial, but it works better on later browser versions. Happy navigation!
Questions:
In your own words, what is inertial navigation?
For what is VOR an abbreviation?
Who "owns" the satellites used for GPS?
How many GPS satellites are there in orbit about the earth?
The accuracy of GPS is actually less than it could be. Why?
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Global Positioning System (GPS) is an international system of global location using satellites in orbit about the earth in conjunction with ground based stations. The user of the GPS system must have a GPS receiver. This device (UVI's Science Division has several economical hand held models) communicates with the satellites which in turn are in contact with the ground stations. The GPS receiver uses the signals of three or more satellites to pinpoint its location on earth. By knowing the precise position of the satellites (the ground stations help monitor position) and the time required for the signal to travel from the satellite to the receiver (typically < 1/10 of a second), the receiver can determine its position. Most receivers are accurate to within several meters, but the new differential receivers are capable of accuracy within centimeters!