// BEGIN editorial data
 var i = 0;
var GPS_wb3 = new Array();
GPS_wb3.ID = "GPS_wb3";
GPS_wb3.ID_WB = 3273576;
GPS_wb3.sPubDate = "12/16/2004 1:49:14 AM GMT";
GPS_wb3.navsectionID = "3032117"
GPS_wb3.appFmt = 2;
GPS_wb3.itemsPerPage = 1;
GPS_wb3.appWidth = 460;
GPS_wb3.appHeader = "HOW IT WORKS|Global Positioning System (GPS)";
GPS_wb3.appFooter = "Source: Department of Defense, IGEB, Smithsonian Institution, Garmin";
GPS_wb3.appNavStyle = 3;
GPS_wb3.appLayout = 3;
GPS_wb3.copyWidth = 304;
GPS_wb3.copyMargin = 9;
GPS_wb3[i++] = new Array("","","","/d/ip/gps_wb3/gps_020603.gif","","", "", "", "", "", "nav", "", "", "129", "149", "", "", "", "", "");
GPS_wb3[i++] = new Array("","How it works","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", "");
GPS_wb3[i-1].body = "GPS is based on a constellation of 24 solar-powered orbital satellites about 12,000 miles above the Earth. A GPS receiver on the ground seeks tracking signals from at least three satellites, then interpolates the data to establish latitude and longitude. If a device can pick up four or more signals, it can also determine a user's altitude.";

GPS_wb3[i++] = new Array("","Who developed it","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", "");
GPS_wb3[i-1].body = "The U.S. military originally built NAVSTAR, as they called it. The first satellite was launched in 1978 and the system was fully operational by the early 1990s. Originally, the military programmed the system for \"selective availability,\" which gave the military 10-meter precision and civilians 100-meter precision. Selective availability was eliminated in 2000.";

GPS_wb3[i++] = new Array("","What GPS is used for","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", "");
GPS_wb3[i-1].body = "Users can get accurate location information across the globe, and most equipment can interpret it to provide speed, distance to a destination and even exact local sunrise and sunset times. Devices are installed in most large ships and aircraft, and the FAA has incorporated GPS as a key part of instrument flight. Many cars use it, and transit companies use it to track trucks and buses. Handheld devices are used by everyone from hikers to land surveyors. The military has adapted bombs with GPS receivers that can guide the weapons to targets.";

GPS_wb3[i++] = new Array("","How accurate it is","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", "");
GPS_wb3[i-1].body = "With the military controls removed, GPS users can now get a precise latitude and longitude to within 10 to 15 meters. Advanced systems known as differential GPS and the Wide Area Augmentation System incorporate the use of stationary ground stations to interpolate signals, and can offer accuracy of 1 to 3 meters or better. The satellites have diagnostic systems and stop sending position data if they're malfunctioning.";

GPS_wb3[i++] = new Array("","Who controls it","","","","", "", "", "", "", "", "", "", "", "", "", "", "", "", "");
GPS_wb3[i-1].body = "The U.S. Department of Defense continues to run the system, though other federal agencies such as the Department of Transportation have taken a role in upgrading and maintaining it. The Coast Guard helps maintain the civilian portions of the system, and private satellite operators provide signals for some advanced interpolation services. The government's Interagency GPS Executive Board coordinates efforts.";

	// END editorial data