This time and date information is transmitted to the control sector. The control sector consists of five unmanned ground stations scattered around the world. The ground stations receive satellite signals traveling at the speed of light. When the signals come in, computers gather and interpret the information, which is supplied on demand to the user sector.
To determine and plot location we need the user sector, which is our hand-held or vehicle-mounted receiver.
Here's what happens when your receiver - the user sector - is activated:
- Satellite transmissions are gathered
- It compares the time signals were transmitted by the satellites with the time they were received by your unit
- Your unit now knows how far the satellites are from your current location
- Your unit tallies up distances from each satellite to triangulate your position
- Your exact position appears on your unit's monitor
Although that's a lot of information to gather and process, it all takes just a matter of moments.
As you can see, all sectors more or less depend on each other to make the entire GPS concept work.
Learn even more about GPS. Continue on or click any of the links below to go directly to that topic.
There are lots of scientific and technological terms associated with the operation and use of the GPS. If you're interested, we've provided a Glossary of these words complete with definitions at the end of this feature. While it's nice to know the technical terms for all the parts and uses, it's not necessary to use and enjoy your GPS.
The space sector contains 24 satellites, each in its very own 12-hour orbit, 11,000 nautical miles above the earth. While orbits are individual and separate, the satellites can sometimes be very close together causing inaccurate readings. Ideal is for four satellites to be at 90 degree intervals. Each satellite has an accurate clock with which it broadcasts precise time messages on a pre-determined schedule indicating its status, what the current date is, and what time the message was sent.