Fundamentals of GNSS
1.1 History of GNSS
GNSS is a natural development of localised ground-based systems such as the DECCA Navigator and LORAN, early versions of which were used in the Second World War. The first satellite systems were developed by the US military in trial projects such as Transit, Timation and then NAVSTAR, these offering the basic technology that is used today. The first NAVSTAR was launched in 1989; the 24th satellite was launched in 1994 with full operational capability being declared in April 1995. NAVSTAR offered both a civilian and (improved accuracy) military service and this continues to this day. The system has been continually developed, with more satellites offering more frequencies and improved accuracy (see Section 1.3).
The Soviet Union began a similar development in 1976, with GLONASS (GLObal NAvigation Satellite System) achieving a fully operational constellation of 24 satellites by 1995 . GLONASS orbits the Earth, in three orbital planes, at an altitude of 19 100 km, compared with 20 183 km for NAVSTAR. Following completion, GLONASS fell into disrepair with the collapse of the Soviet economy, but was revived in 2003, with Russia committed to restoring the system. In 2010 it achieved full coverage of the Russian territory with a 20-satellite constellation, aiming for global coverage in 2012.
The European Union and European Space Agency Galileo system consists of 26 satellites positioned in three circular medium Earth orbit (MEO) planes ...