Volpe Journal Summer 2000
Back to On Course with GPS
The History of Air Navigation
In 1903, the historic first flight of the Wright brothers and the subsequent development and growth of the air transport industry meant that navigation techniques appropriate for air transport were needed. In the 1930s, land-based radio beacons were used to provide bearings for aircraft from airfield to airfield. During World War II, several radio navigation systems were developed, the best-known being LORAN or Long Range Aid to Navigation. Positions were determined by the timing of signals received from different LORAN transmitter stations.
In 1957, the Soviet Union launched Sputnik, the first space satellite. One year later, in 1958, the United States launched Explorer I. With the advent of the satellite, scientists came to realize that placing radio transmitters in space could solve problems posed by land-based radio beacons. A transmitter high above the earth, which is sending a high-frequency radio wave with a special coded signal, can cover a large area with great accuracy. Satellite navigation promised that, for the first time, aircraft would be able to determine their positions at any time, anywhere in the world.
In the mid-1960s, the US Navy developed TRANSIT, the first operational satellite positioning system, to provide more accurate positions for ships and submarines. Six satellites gave worldwide coverage every 90 minutes and provided positions that were accurate to within 200 meters.1 TRANSIT was effective, but it lacked 24-hour availability.
During that time period, the US Navy and Air Force worked on a number of systems to provide navigation capability for a variety of military applications. These systems often were incompatible with one another. Eventually, in 1973, the Department of Defense directed the development of a global satellite system. The basis for the new system was atomic clocks carried on satellites, a concept that was successfully tested in an earlier Navy program called TIMATION. The Air Force planned to operate the new system, which was the Navstar Global Positioning System. It has since come to be known simply as GPS.
In 1994, the Senate Armed Services Committee, describing the need for a research study funded by the Department of Defense on the future of GPS, said, "It is clear that GPS offers the potential to revolutionize the movement of goods and people the world over. Civil and commercial exploitation of GPS could soon dwarf that of the Department of Defense and lead to large productivity gains and increased safety in all transportation sectors."
Since the mid-1980s, the Volpe Center and it's Center for Navigation has been involved with the use of GPS in all modes of transportation. In the early 1990s, the Center for Navigation made history when a commercial vessel was tracked for the first time in the St. Lawrence Seaway using a GPS-based system that the Center had developed. The system was based around a half-dozen portable units that used GPS to determine their location. The portable units then transmitted that information to a shore-based control center responsible for scheduling ships waiting to pass through the locks.
In 1995, the Center designed and installed a similar, but much more advanced, system in the Panama Canal. This system consists of 150 mobile units that communicate with a control center via a shore-based UHF communications network. The mobile units consist of a GPS receiver and antenna, a laptop computer, and another radio antenna for communications with the control center.
Advanced GPS navigation systems also are planned for installation in Honduras and Nicaragua as part of a Central America Reconstruction Project, sponsored by the US Agency for International Development. The intention is to provide recovery and reconstruction assistance to the region, which is still suffering from the effects of damage caused by Hurricane Mitch in 1998. The new systems will provide accurate vessel tracking and navigation in harbors and waterways in all weather conditions.
In addition to systems for ships, for the past five years, the Center for Navigation also has been working with a number of international clients on the use of GPS for air navigation. This work is described in the accompanying article.
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