A Condensed History of the Global Positioning System (GPS)
Like the telephone or the internet, the Global Positioning System (GPS) is one of many technological advancements that has tremendously impacted human life. From its original military applications to its wider public release, the creation of GPS is a long and strange story worthy of several books. Therefore, today I am giving you the condensed version that fits in a single blog post.
(A replica of Sputnik 1, the first artificial satellite in the world to be put into outer space)
Development of the GPS can be dated back to 4th October 1957 with the launch of Sputnik 1 by the Soviet Union. As we all know, this kickstarted the Space Race between the US and Russia. However, what you may not know was this also marks the first steps in developing the predecessor to GPS. When observing the radio signals broadcasted by the Sputnik satellites, two physicists at John Hopkins University’s Applied Physics Laboratory, Dr. William Guier and Dr. George Weiffenbach, discovered that they could accurately calculate their location through the doppler effect – as the satellites orbited closer to their point of observation, the frequency of its signals increased and decreased as it moved away. From there a simple question was asked: if they could locate a satellite in orbit, could you turn that upside down: Could you locate something on Earth from space using a satellite?
This discovery led to the development of the GPS precursor, TRANSIT. First tested in 1960 and fully operational by 1964, TRANSIT used a simple five satellite constellation and was mainly developed for the US Navy and their submarines armed with ballistic missile. The precursor was not as accurate or as fast as the GPS. TRANSIT had an accuracy of 25 metres (as opposed to GPS’s 10 metres), but only in two dimensions and it could only ping a location every few hours. However, it proved that a satellite constellation-based navigation system was feasible.
(The USS George Washington, the United States's first operational ballistic missile submarine.
TRANSIT was developed to pin-point the location of these submarines.)
Other important developments and precursors that contributed to the creation of GPS included Program 621B (1962-1972), a series confidential USAF studies which allowed for altitude to be measure via satellite (as opposed to just latitude and longitude) and developed prototype GPS receivers; Sequential Collation of Range (or SECOR, 1964-1969) satellites which were developed by the US Army for geodetic surveying; and finally, the Timation satellites (1967, 1969, 1974), which launched the first atomic clock into space for accurate timekeeping. GPS was created by combining the best elements of all these developments.
On Labour Day weekend of September 1973, the Lonely Halls Meeting took place in a vacant Pentagon (as everyone was away on Holiday). The US Department of Defence, realising the potential of a satellite-based navigation system, discussed plans to develop the Defense Navigation Satellite System (DNSS) which every branch of military could use, as opposed to each one creating and maintaining their own. DNSS would eventually be renamed Navstar (Navigation System using Timing and Ranging) and finally, Navstar-GPS.
(A NAVSTAR Block-I satellite)
1978 marks the first experimental GPS satellite launch. This was the first of ten Block-I satellites, launched between 1978 to 1985 (one was destroyed in a failed launch). These satellites were merely for testing purposes. An experimental constellation to see if the GPS was a viable concept. However, in 1983, before any major breakthrough happened, Korean Airlines flight 007 was shot down by a Soviet jet after it mistakenly entered prohibited airspace. Following this event, US President Ronald Reagan announced that GPS would be available for the wider public (once complete) given the benefits it would bring to navigation and so that such an event would not be repeated.
Development of Block-II began in 1983. Nine satellites were launched between 1989 to 1990, and this was the first operational GPS constellation. In fact, the Gulf War (1990-91) was the first major conflict where GPS was used extensively. In the following years, more Block-II satellites (Block-IIA, 1990-97) were launched and by April 1995, GPS was declared “Full Operational Capacity” by the Air Force Space Command. However, the publicly available GPS was hindered by a policy known as “selective availability” which degraded the signal quality for civilians. Thankfully, in May of 2000, selective availability was discontinued, however, the US still has the power to degrade or even shut off GPS in specific regions.
(A GPS Navigation device in a taxi. Photo by Paul Vlaar, via WikiMedia Commons)
Currently there are 12 Block IIR (1997-2004), 7 Block II R-M (2005-2009) and 12 Block IIF (2010-2016) satellites power the GPS constellation. Improvements to GPS and new satellites continue to be researched and developed, with Block IIIA satellites currently being manufactured and its first launched is scheduled in September 2018. The more advanced Block IIIF satellites are scheduled start development in 2026, with its launches lasting until 2034.
We have only to look forward towards the future of GPS. However, it’s fascinating to look back at how the GPS came to be. From its initial intention as a missile guidance system, to becoming an invaluable part of modern navigation, we owe a lot to GPS, to the scientists who made it possible, and to those upgrading it as we speak, to give us more a reliable and accurate GPS.