Garmin SL60 - Manual (Page 101)

Introduction to GPS Navigation
GPS
Overview
The Global Positioning System (GPS) is a
constellation of 24 satellites in six orbit lanes
10,898 nautical miles above the earth at an
inclination angle of about 55 degrees from the
equator. Each satellite orbits the earth twice in 24
hours.
The GPS was developed and the satellites launched
by the U.S. Department of Defense with the original
intent of supplying highly accurate position fix
information for military applications. In recent
years, commercial applications for the information
provided by this system have steadily increased in
the civilian sector. Some of the more popular
civilian uses of the system include surveying and
position fix data recording for civil engineering
applications, and a broad range of marine, aviation,
and terrestrial navigation applications.
While orbiting the earth, each GPS satellite
transmits complex streams of data containing the
operational status and orbital location of all the
satellites in the system. The Apollo SL50/60
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Introduction to GPS Navigation