Principles of Operation
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user equipped with a GPS tracking receiver, who is on or near
the Earth’s surface. The Global Navigation Satellite System
(GLONASS), is the Russian Federation Ministry of Defense
counterpart to GPS. At any one time, with a standard 15 degree
angle, up to 10 or 12 GPS satellites are visible from any point
on earth. When a receiver can also track GLONASS satellites,
between 10 and 16 satellites are visible.
For information on the current status of the GPS constellation,
visit http://tycho.usno.navy.mil/ or
http://www.navcen.uscg.gov/. For GLONASS, visit
http://www.glonass-center.ru/frame.html.
Despite numerous technical differences in the implementation
of these systems, both GPS and GLONASS have three essential
components:
• Space – GPS and GLONASS satellites orbiting
approximately 12,000 nautical miles above Earth and are
equipped with a clock and radio. These satellites broadcast
digital information (ephemerides, almanacs, time frequency
corrections, etc.).
• Control – Ground stations located around the Earth that
monitor the satellites and upload data, including clock
corrections and new ephemerides (satellite positions as a
function of time), to ensure the satellites transmit data
properly.
• User – The community and military that use GPS/
GLONASS receivers and the corresponding satellites to
calculate positions.
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