Technology has achieved many useful developments in satellite
navigation systems that allow a small electronic device to navigate its
exact location (Longitude, Latitude and Altitude) through satellite.
When it knows its position, the navigation device calculates the
navigation information including terrain, directions, roads and more.
Nowadays, most vehicles come with the satellite navigation devices
pre-installed in them. These devices are generally used by motor
vehicle drivers, military, outdoorsmen, boaters and for other military
applications.
The well known satellite system that is fully functional at the time of
this writing is the GPS or the Global Navigation System. GPS in the
United States contains 24 to 27 satellites orbiting at an altitude of
approximately 20,000 km with an inclination of 55 degrees in six
different planes.
The Russian counterpart to GPS is called the GLONASS, which is derived
from GLObal Navigation Satellite System. Though the initial satellites
for GLONASS were launched in 1982, the system was not fully operational
till 1995. The GLONASS has deteriorated to only 12 satellites, due to
economic difficulties. The Russian GLONASS constellation is expected to
become fully functional by 2010 and there are plans to include India as
well.
The European Union is working on EGNOS derived from European
Geostationary Navigation Overlay System. It consists of 3 satellites
intending to supplement the GPS and GLONASS systems by determining the
accurate signals and position with in 5 meters. It is expected to
function in 2006.
The European Space Agency is working on introducing an alternative to
GPS, called Galileo. The receivers will be able to combine the signals
of 30 Galileo satellites and 28 GPS satellites to get highly accurate
positions.
There are many satellite navigation systems yet to launch in several
countries. The Satellite system of France is called the DORIS (Doppler
Orbitography and Radio-positioning Integrated by Satellite) The Chinese
system is called BEIDOU, but these satellite systems do not come under
the caliber of GPS, GLONASS and Galileo.