Evolution of the Global Navigation Satellite System


Global Navigation Satellite System

The 22nd October 1707 will forever go down as the saddest day for the Royal Navy and the maritime community as a whole. The Scilly naval disaster that took place on this date claimed 1550 sailors and four warships at the Isles of Scilly. This naval disaster was blamed on several factors chief of which was the navigator’s inability to accurately establish their position. This devastating loss led to the Longitude Act of 1714 in which the British government offered to award prizes to anyone who could solve or improve the methods used to determine longitudes. It is unfortunate that none of the large prizes were ever awarded. However, this initiative led to the development of many navigation techniques and equipment later yielding in the development of the Global Navigation Satellite System (GNSS).

What is GNSS?

GNSS is a satellite-based system that could be used to pinpoint the location of a user’s receiver anywhere in the globe. It offers real-time accuracy and continuity of signal coverage as wide as possible. It can be used on road, air, rail and maritime transport. There are numerous types GNSS systems currently in operation they include:
  • EGNOS
  • GALILEO
  • GPS
  • GLONASS
  • BeiDou
  • RNSS
  • QZSS

The GNSS journey

The first ever satellite navigation system, the Transit, was deployed in the 1960’s by the US military. Its operations were based on Doppler effect hence it traveled on well-known paths while broadcasting their signals on known radio frequency. The frequency received from the receiver will vary slightly from the broadcast frequency. The receiver is able to determine its location by monitoring this frequency shift over a short time interval. Several of such measurements when combined with a precise knowledge of the satellite’s orbit a particular position can be fixed. The Transit, however, had its own shortcomings, it was marred by orbital errors owing to variations in gravity and radar refraction. These problems were however resolved in the 1970’s by Harold L Jury.
GNSS was only available to the military. It was not until 1983 that GPS units became available to civilians. This was after a passenger plane was shot down over Soviet airspace prompting the President Ronal Reagan to give a directive that saw the technology availed worldwide. Further efforts to make GPS available to everyone were witnessed in 1989 when the first satellite component of the current GPS network was launched into orbit. This exercise was completed in 1995, the network contains 24 satellites that circle the earth’s orbit approximately twice a day. This improved the accuracy and reduced the price of GPS units. It was after this that
  • EGNOS – It started its initial operation in 2005. Its accuracy is more than two meters. It was officially launched in 2009.
  • GALILEO – It started in 2003 and is still in progress.
  • GLONASS – It was first launched in 1982 and its last launch was in June 2018. Its accuracy is between 2.8 and 7.3 meters.
  • BeiDou – It was first launched in October 2000 while the last launch was in July 2018.

Summary

GNSS has come far. Over the period, it has witnessed many improvements that have seen it become more accurate and reliable. More developments are expected going forward hence the evolution is far from over. How far the evolution will go can only be left to time.

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