GPS Tracking System - How Its Components Work

Born of the best minds from a concept so simple is an exceptional

complex system, the GPS tracking system. It is made up of three

componentsL satellites that orbit the earth, control and monitoring

stations and the GPS receivers. It is a radionavigation system

providing reliable positioning, navigating, and timing services not

just for the military but also to civilian users as well in any part

of the world. The GPS tracking system has drastically changed the

world of navigation through land, sea and air, in all weather, 24/7.



The Global Positioning System (GPS) is a U.S. space-based

radionavigation system that provides reliable positioning, navigation,

and timing services to civilian users on a continuous worldwide basis

-- freely available to all. For anyone with a GPS receiver, the system

will provide location and time. GPS provides accurate location and

time information for an unlimited number of people in all weather, day

and night, anywhere in the world.

In the 1960s the U.S. Navy and Air Force worked together on a number

of systems that would be able to provide a variety of navigation

applications. In 1973 the Department of Defense aimed to direct the

services in unifying their systems. The concept of the tracking

system would be atomic clocks onboard satellites was tested

successfully by an earlier Navy program called TIMATION. The Air

Force would operate the new system called the Navstar Global

Positioning System. From then on, it has since been known as simply

GPS or Global Positioning System.

The GPS tracking System Satellites

Today's GPS Operational Constellation is funded and controlled by the

U.S. Department of Defense and being operated by the U.S. Military.

It is comprised of three major components: a "constellation" of

satellites in Earth orbit, ground stations that controlled the system

and receivers hand carried by the users. It was so designed so that

these receivers could be made small and inexpensive and would not

require atomic clocks.

The GPS tracking system is an aerospace technology comprising of at

least 24 operational satellites at all times. Each satellite is on a

circular orbit 20,000 kilometers above the Earth on a 12-hour period.

In order to make sure that these satellites are detected from anywhere

on the surface of the Earth, the satellites are divided into six

groups having four space vehicles each. The six orbital planes

completely surround the Earth, equally spaced 60 degrees apart and at

an angle of about 50 degrees with respect to the equatorial plane.

Each group is assigned a different path to follow. The orbit altitude

is such, that the GPS satellites recapitulate the same ground track

and configuration at approximately over any point each in 24 hours.

The GPS tracking system's navigation message consists of time-tagged

data bits that mark the time of transmission of each subframe at the

time they are being transmitted by the space vehicle. A data bit

frame consists of 1500 bits divided into five 300-bit subframes and a

data frame is being transmitted at an interval of 30 seconds. There

are three six-second subframes containing orbital and clock data.

Precise clock corrections are sent in subframe one and orbital data

sets or ephemeris data parameters for the transmitting space vehicle

are sent in subframes two and three. Various pages of the system data

are being transmitted in subframes four and five. So the GPS tracking

system has an entire set of twenty-five frames or 125 subframes

creating the complete navigation message sent over a 12.5-minute

period.

The GPS Tracking System Equipment on the Ground

Ground stations are used so that each satellite orbit are accurately

tracked. The GPS tracking system has ground stations which is

comprised of a receiver and antenna, as well as communication tools to

transmit the data to the data center. When the GPS satellites supply

specially coded signals, the omni-directional antenna at each site

picks up the signals and that is processed in a receiver. The

receiver then separates the signals in various channels for a

particular satellite and frequency at a particular time. Once the

signals are isolated, the receiver now decodes them and splits them

into individual frequencies to calculate position, velocity, direction

and time anywhere on Earth.

At least four GPS satellite signals consisting of space segments are

used in computing positions in three-dimensional locations - latitude,

longitude and altitude - and the time offset in the receiver clock.

All GPS tracking system satellites have synchronized operations so

that the signals are transmitted at the speed of light to the

equipment on the ground. Each GPS satellite broadcasts data

indicating its location and current time.

Since the GPS tracking system sites are constructed throughout the

world and are being monitored by different institutions worldwide,

there are many different data center locations. The role of the data

center is to both monitor and control the GPS tracking system

stations. The data center uses an automated computer system in

retrieving and analyzing data from the receivers. Once processed, the

data, including the original raw data, are sent to scientists around

the glob for use in various applications.

From laboriously built landmarks by our ancestors to shooting the

stars to chronometers to satellites, our technology has evolved faster

than we could ever imagine. The GPS tracking system is the most

recent and significant advancement in navigation and positioning

technology. This new constellation of artificial stars serves this

important need for both the military and civilian users and is now

fast becoming important in everyday life.