You may know about Global Positioning Satellites or GPS from TV shows like JAG and Pensacola where it is seems our intrepid heroes can determine the position of submarines and those engaged in criminal activity with pinpoint accuracy, but have you ever wondered how a GPS system actually works and where it came from? Read on to find out how Global Positioning Satellites work and how this useful technology originated.

During the 1960’s U.S. Navy and Air Force personnel applied their minds to creating a system that would enable navigation capability for a range of different military applications. As it turned out most of these systems were not compatible with each other and as early as 1973 the Department of Defense made concerted efforts to provide for the cohesion of their systems – the basis of which was to make use of atomic clocks which would be carried on satellites.

A few years earlier a system called Timation had been extensively tested with success and this would be the foundation for the new compatible system technology.

What sprang out of this intense effort to enhance military and naval technology systems would be dubbed the ‘Navstar’ Global Positioning System. It was initially operated by the Air Force and it is this groundbreaking technology which would eventually become familiar as the Global Positioning Satellites we know today.

This brand new brain child would see three components namely: several ground stations that would control the system, a group or “constellation” of satellites in Earth orbit, and receivers carried by GPS operators or users coming into play.

Ultimately the system would be of such a nature that receivers wouldn’t need atomic clocks. This was, in fact, revolutionary since it meant that Global Positioning Satellites could be reduced in size, fit into the palm of ones hand and be manufactured both quickly and cheaply.

The GPS Satellites

The first satellite launches made their debut in 1978 but in 1989 it’s second-generation or ‘Block II’ was brought into being – the second set of satellites. Recent GPS technology is made up of at least 24 Block II satellites. In 1995 the Global Positioning Satellites were deemed fully operational.

MANPACK GPS Receiver

The PSN-8 or ‘Manpack’ portable GPS unit was the first GPS receiver available to soldiers in the field and from the year 1988 to 1993 about 1400 of these satellite communication devices were manufactured.

In 1993 the Manpack would be superceded by the newer hand held Precision Lightweight or PLGR GPS Receive. This little device would come to be known as the ‘Plugger’ and was a little bit like the civilian receivers we use today, the difference being that they were able to use more precise GPS signals.

How GPS Went Global

Originally Global Positioning Satellites were designed so that ordinary people like you and me, would not be able to obtain the same accuracy as the military did but it is reported that both civilian as well as military applications were intended for GPS systems right from its inception.

In 1983 the Korean Flight 007 crash was determine to have been ‘preventable’ had the on-board crew had more advanced navigational tools at their disposal – and it was at this juncture that President Ronald Reagan issued a directive guaranteeing that GPS signals would be available (free of charge) to the global community. It was this foresight that led to a booming commercial market for GPS technology and its many applications today.

A phase of steady growth ensued with a growing number of both civilian and military users making use of Global Positioning Satellites in the 1990’s but it was during the Persian Gulf War in 1991 that it became a household name. GPS technology was used so frequently to aid the conflict resolution that military equipped systems became scarce.

To buffer the situation, the Department of Defense used civilian GPS systems and altered the transmissions to allow civilian receivers access to more precise military signals.

But How Do Global Positioning Satellites Work?

Although the technology that enables GPS to work is highly complex the way in which it works is simple by contrast. GPS satellites work by sending out signals to equipment located on the ground. GPS receivers only receive satellite signals and don’t actually transmit them.

For this sequence of events to work properly the GPS receivers need a clear view of the sky and so are only used outdoors and don’t work very well in areas where there is dense vegetation such as forests or in areas that contain many tall buildings.

GPS systems also require a very accurate time reference to relay accurate information and this precision is fueled by atomic clocks located at the U.S. Naval Observatory. Each GPS satellite has atomic clocks within its capsule.

The GPS satellite transmits data that shows where it is and the current time. Each and every satellite synchronizes operations so that the repeating signals are transmitted simultaneously.

The signals move at the speed of light and connect with a GPS receiver at slightly staggered times. This is simply due to the fact that certain satellites are further away than others.

By making an estimate of the time it takes for a signal to reach the receiver, the distance to the GPS satellites can be determined. For example, if the receiver estimates the distance to at least four GPS satellites, it is then able to calculate its position in three dimensions.

At any given time there are 24 Global Positioning Satellites in operation and these are operated by the U.S. Air Force and will orbit within a period of 12 hours. The ground stations can accurately track each satellite’s orbit.

So how does the GPS receiver know where each satellite is? The data is included in the satellite transmissions and on estimating how far away a satellite is a receiver also knows that it is located at a point on the surface of an imaginary sphere centered at the satellite.

Next it calculates the sizes of several spheres – one for every satellite and…voila the receiver is located where these spheres intersect each other. So know you know where you are!

Not bad for a technology not even three decades old! Global Positioning Satellites are now the stalwart of many military, engineering, commercial, nautical, news and civilian applications. In fact, since most modern day communication relies heavily on GPS systems, including the safety of our airplanes we probably can’t do without them. Global Positioning Satellites have undoubtedly saved many lives and will continue to do so in years to come.