Space plays role in everyday communication Published Aug. 15, 2006 By Capt. Nicole Walters 90th Space Wing Public Affairs F.E. WARREN AIR FORCE BASE, Wyo. (AFPN) -- Cell phones used to be a luxury, and you were the cool kid on the block if you had one. Now cell phones have become indispensable. You can talk virtually anywhere, anytime to anyone in the world and send pictures, video and text messages. But how does your cell phone work? And why is space vital to the equation?A cell phone is actually a radio that sends signals to a tower. All the little bars represent your reception with the tower. The city is broken into small cells that allow a large number of people to use their phones simultaneously, and cells will transfer you from one cell to another when you travel. But how does the cell phone company know you from everyone else? There are several codes programmed into your phone. A system identification code, which is called SID, is a unique five-digit number the Federal Communications Commission assigns to each carrier. The electronic serial number is a 32-bit number programmed into the phone when it was manufactured, and the mobile identification number is your phone number. So you turn the phone on, and it searches for control channels at the base station. If the cell phone can't find any it displays "no service." Let's say the phone is able to reach the base station via the tower. The mobile telephone switching office compares SIDs, and then the phone will transmit a registration request. The switching office tracks you on the database and pinpoints your location on the grid. It then will match frequencies between you and the person you called. Now you are good to go, right? Suppose you drive your car into a ditch because you are talking on your cell phone. Fortunately, in 2000 the FCC began requiring cellular phone service providers to be able to identify via the Global Positioning System the location of a cell phone caller who dials 911. Cellular phone service providers must be able to identify your location. While large cities have equipment to track you via GPS, some local or small cities don't have the equipment. They have to do it the old fashioned way of calling the provider to get the GPS information. GPS consists of 24 Earth-orbiting satellites. The military developed and implemented these as navigation tools, but they were soon opened up to everyone else. The gravity of the GPS is almost too much to grasp; each satellite weighs between 1.5 to 2 tons and rotate the Earth twice a day. The 2nd Space Operations Squadron at Schriever Air Force Base, Colo., is constantly working overtime. Squadron members perform the command and control mission for the GPS satellite constellation, which makes up more than 40 percent of Air Force Space Command's active satellites. That means the GPS system is constantly working, because the squadron is constantly working. A GPS receiver locates four or more satellites, and uses a complicated math process called trilateration to plot your distance to the four satellites and thereby deduce the location. Actually, it deduces two locations: one on Earth and one deep into outer space. Since you aren't in outer space, it throws out that answer and keeps the one of you on Earth. "Besides being used in individual cell phones, GPS plays a critical role in overall cell phone (and other phone) lines and services," said Edward Parsons, 50th Space Wing Public Affairs chief. "GPS provides vital timing information to keep their systems operating smoothly." Each GPS satellite carries four clocks synchronized to GPS time (coordinated universal time). The clocks are so precise, they are accurate to within one-millionth of a second. So while you just got a bump on the head and a banged up car for talking on your cell phone while driving, you can at least be assured any necessary emergency vehicles can find you. GPS information is used in millions of ways. It's used to plot the Earth's volcanoes, note locations and track the movement of protected species. The program that began as a military tool is now an invaluable service and a $10 billion commercial industry.