NAVSTAR was invented and developed by the US during the height of the Cold War. It was primarily meant for military use but after a Korean airliner was accidentally shot down the US administration at the time decided to open up their system for the ‘greater good.’
Since that time NAVSTAR, now commonly referred to as GPS (Global Positioning System), has revolutionised transportation around the world for mariners, pilots and car drivers alike.
The functioning of the GPS system is very simple. There are currently a constellation of 24 satellites, arranged in orbit so that four are always in line-of-sight to any spot on the Earth.
These satellites contain atomic clocks, the most accurate chronometers so far developed by mankind. These keep and broadcast a time code that is accurate to a few nanoseconds (nano = 1 billionth of a second). This time code is then received by a GPS receiver that uses the information from four satellites to triangulate its exact position. This can only be done because the atomic clocks provide such accurate time. If a clock on a GPS satellite was even just one second too slow or fast, the positioning information could be as much as 200,000 miles out (because of the distance light and therefore radio waves travels in that time).
As the timing source from GPS systems are so accurate they are ideal to be used as a reference for a NTP server. NTP (network time protocol) servers use a timing source to synchronise all machines on a network to that time. A dedicated GPS NTP server can receive the time signal from the NAVSTAR system and synchronise an entire network to within a few milliseconds.