GPS (Global Positioning System), a constellation of 24 NAVSTARs (Navigation Satellites for Time and Ranging) in six groups of four owned and operated by the Department Of Defence (DOD), is the first positioning system to offer highly precise location data for any point on the planet, in any weather. Today’s GPS receivers are extremely accurate. WAAS (Wide Area Augmentation System) can give us even better accuracy to an average of up to five times better. We can also get better accuracy with Differential GPS (DGPS) to an accuracy of three to five meters. For example Military-approved equipment can pinpoint accuracy with one meter. The signals that are transmitted by GPS satellite are two low power radio signals, designated L1 and L2.A GPS signal contain information such as which satellite is transmitting information, current date and time, and orbital information. There are some actors that can degrade the GPS signals, which are explained briefly in the foregoing papers. There are wide ranges of applications of GPS on land, at sea, and in the air .The first and most obvious applications of GPS is the simple determination of a “position “ or location. In future this GPS may become very much accurate as currently it is.
Travellers, sailors and explorers used to find their way using a compass, and by measuring the positions of the Sun, Moon and Stars. Today, all we need is a GPS (Global Positioning System). It looks like a mobile phone. When it is switched on it can tell us where we are any where in the world .It will give us a map reference .It also shows our height above sea level, and if we are moving, how fast we are going and in which direction. The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 NAVSTARS placed into orbit by the U.S. Department of Defence. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.
The 24 satellites that make up the GPS space segment are orbiting the earth about 12,000 miles above us. They are constantly moving, making to complete orbits in less than 24 hours. These satellites are travelling at speeds of roughly 7,000 miles an hour. GPS satellites are powered by solar energy the have backup batteries onboard to keep them running in the event of solar eclipse, when there’s no solar power. Small rocket boosters on each satellite keep them flying in the correct path.
Here are some interesting facts about the GPS satellites
- The first GPS satellite was launched in 1978.
- A full constellation of 24 satellites was achieved in 1994.
- Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.
- A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.
- Transmitter power is only 50 watts or less
The U.S. Department of Transportation's Civil GPS Service has designated NOAA to be the federal agency responsible for providing accurate and timely Global Positioning System (GPS) satellite ephemerides ("orbits") to the general public. The GPS precise orbits are derived using 24-hour data segments from the global GPS network coordinated by the International Geo dynamics GPS Service (IGS). The reference frame used in the computation is the International Earth Rotation Service Terrestrial Reference Frame (ITRF). In addition, an informational summary file is provided to document the computation and to convey relevant information about the observed satellites, such as manoeuvres or maintenance. The orbits generally are available two to six days after the date of observation.