The dawn of the modern eraFrom the 17th century onwards, discoveries, inventions and improved techniques followed each other in rapid succession, each one allowing navigators to plot their position or course with ever-increasing accuracy and reliability.But modern navigation really only began in the 1920's, with the introduction of ground-based radio systems.Beginning with radios that allowed navigators to locate the direction of shore-based transmitters when in range, ground-based systems used the same principle later adopted by GPS: measuring your distance from a series of transmitting towers to pinpoint your location. It was a breakthrough, but not without its drawbacks. Range and accuracy was limited. The LORAN system's towers, for example, had a range of about 800km accurate to about 250 metres. And because it sends signals over the earth's surface, a ground-based system can only determine a 2D position. Which means you can't measure altitude. So the system is useless for aviation purposes. From towers to satellites The introduction of artificial satellites in the early 1960's brought more accurate line-of-sight radio navigation signals. Initially, satellites were used in 2D systems like the US Navy's Transit. But though it may have been relatively simple, Transit was reliable and paved the way for a system that would transform navigation once and for all: The Global Positioning System, or GPS.Once GPS came along, ground-based systems were effectively obsolete. Though some are still in use today, the first global ground-based system (OMEGA) was phased out in 1997. The message was clear: the future lies in the stars.Want to read more about the GPS revolution and how it works? Click here.<<