Global Positioning system

The History of GPS

The Global Positioning System (GPS) has its roots, ultimately, in the struggle of humans to correctly identify where we have been, are, and will be. The result of this struggle was to begin building maps. The earliest maps were simple mental pictures of the terrain around a group’s camp or hunting area. The first maps produced date to more than 5,000 years ago, and are found on clay tablets from the middle east. The Greeks and Romans began surveying for roads and new settlements using methods that differed little up to last century.
Then, in the 18th century, the French began using triangulation to create maps of their country. Later, this was combined with trilateration to map entire continents and was referenced to stars. These maps were often hundreds of meters off even for the most painstaking surveys conducted.
These problems of using line of sight surveying techniques were first addressed during and after WWII. The idea of using radio waves to locate and track ships was introduced in an attempt to coordinate forces during the war effort. This gave birth to the precursors of GPS, the OMEGA and LORAN systems, each of which had major problems. The main problem was that each of these systems were ground base, and to be used successfully, one needed direct line of sight with a transmitter (OMEGA does provide global coverage but with low accuracy and LORAN has accuracy of 450m but only covers 10% of the planet).
The next step was to take the above ideas into space. The first space based navigation system was called TRANSIT, it is still in use today. However, this system used Doppler shift to calculate position, and accuracy was only attainable if the receiver sat in one position for a couple of hours, and thus was only good for large-scale navigation.
TRANSIT had some majors problems that GPS was specifically designed to overcome. These included the large gaps in coverage time due to TRANSIT only having 6 satellites in near circular polar orbits, which meant only a few minutes of coverage for every 90 minutes. Also, this earlier system did not give accurate measurements when the receiver only sat still for a few minutes, it needed much longer to calculate positions.
Today, GPS is a fully functioning worldwide system used for everything from real-time navigation to mapping your hometown! To further appreciate the time and resources that built this system, let’s take a look at the specifications.
Actually, today’s GPS system grew out of two US military projects run during the 1970s. These resulted in the first generation of satellites being launched during the late 70s. The 1980s saw another wave of satellites being built and the US government guaranteeing the ability of civilian use. The system reached Initial Operation Capability (IOC) in 1993 with 24 first generation (Block I) satellites deployed, and in 1995 reached Full Operation Capability (FOC) with 24 second generation (Block II) satellites deployed.
So, what exactly is GPS?
We know many of you have probably asked or been asked this question more than once. Well, we are going to tell you in simple terms. GPS is:

1. a space based positioning system used for navigation, tracking and mapping
2. it is designed and maintained by the US Military
3. truly global in scope
4. available every hour of every day all year long, and is cheap to use!
   

Now that we have a basic idea of what GPS is, and why it was developed, let’s look at how it actually works. Basically, what are the actual components (human and machine) that allow this amazing utility to do what it does.