Global Positioning System

Our ancestors built monuments and landmarks to know where they were positioned but technology has become so advanced now that with the help of satellites, people will know where exactly they are positioned if they have a GPS receiver and a clear sky.


The Global positioning system or GPS is a network of 24 satellites placed into orbit by the US Department of Defense. It is a satellite based navigation system which was originally intended only for military use but was later made available for civilian use also. GPS works 24x7, under any climatic conditions and there are no charges levied to use GPS. The GPS was built at a cost of 12 billion $ and the face of navigation has changed forever.

Working of the GPS

The GPS satellites have a well-defined orbit on which they circle and transmit signals to the earth. This information is taken by the GPS to calculate the users exact position. The difference in the time between when the signal was sent to when the signal was received helps in knowing how far the satellite is and helps the receiver in determining the user's position.

IF the GPS is locked on to atleast 3 satellites, a 2D position ( Latitude and longitude) can be figured out and if it is locked on to more than four satellites, then a 3D position of the user ( latitude, longitude and altitude ) of the user is determined based on which speed, distance to destination, sunrise, sunset can be calculated.


The accuracy of the GPS receivers is very accurate as they use parallel multi-channel design. Even in forests or places where there are tall buildings, the receivers transmit accurate signals as they get locked on immediately when turned on. These GPS receivers are accurate to within 15 meters on an average.

The GPS receivers fitted with Wide Area Augmentation System (WAAS) are accurate to the point of less than 3 meters.

The Satellite system

The 24 satellites of the GPS system are 12000 miles above us. They make 2 orbits within 24 hours at a speed of 7000 miles/hour. The GPS satellites use solar energy. They have backup batteries on board to keep them running when there is solar eclipse and to keep them from going in the right path there are small rocket boosters on board.

NAVSTAR is the other name for GPS kept by the US Department of Defense. Some features of a GPS are:

  • The first GPS was launched in the year 1978
  • The constellation of 24 satellites was achieved in 1994
  • Each satellite can work for 10 years which will then be replaced by new ones which will be placed in orbit.

The power which is transmitted is 50 watts or lesser than that. A GPS satellite has 2 low powered radio signals L1 and L2. L1 signal is used by civilians. These signals can pass through clouds, plastic and glass but cannot pass through buildings and mountains. It has 3 different codes. One identifies which satellite is transmitting information, the other one shows information about where each satellite is during the day and the third one gives important information about the status of the satellite, date, time etc which is important for determining the position.

There are a few factors that affect the accuracy of GPS.

The signals slow off when passing through atmosphere or when it reaches tall buildings or mountains before it reaches the receiver. There may be timing errors when the receivers clock doesn't match with the atomic clock on the satellite. The signals don't work underwater or underground and therefore the reading may not be possible.

Uses of GPS

The obvious and most important use of a GPS is to determine Location or position of a place or person. E.g once a person was stranded in a place for 2 days and with the help of a GPS, she was rescued. Measuring the Mt.Everest also became easier with the help of a GPS.

The second use is for navigation. People can get around to places quickly if they have a GPS receiver,. It helps in the navigation on air, water and land.

GPS system is also used for tracking. It is very important to track emergency vehicles like ambulances or even for business purposes, if they are able to track their vehicles it will improve the efficiency and running of the business.

GPS can track, locate and navigate places and objects. This helps in mapping places and routes, rivers and everything possible on the earth. Mapping makes everything run very efficiently and smoothly.

GPS uses a highly accurate atomic clock with the help of which our ground GPS receivers can set their clocks to precision. As time is such an important commodity, everything can be made to run with clockwork precision. Most of the investment banks, computer companies, radio and television stations use this method to time themselves so that a synchronization is maintained throughout.

GPS are now being used in cars, planes, laptop computers. Slowly its going to become a necessity just like mobiles and computers.

The GPS has received an award in 2003, the National Academy of Engineering Charles Stark Draper Award. One of the developers also received the National Medal of Technology award in 2006. The GPS team were also selected as winners for the Robert. J. Collier trophy award one of the most prestigious aviation awards in the US.