Gps System Segments - Honeywell BENDIX/KING KLN 94 Pilot's Manual

Honeywell gps receiver user manual
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Appendix F GPS Primer
quickly lock on to the satellites in view. Otherwise, the receiver would
have to look for each of the 24 satellites to determine which ones could be
used.
Almanac data is very crude data which describes the approximate orbital
position of the satellites. Each of the 24 satellites transmits the almanac
data for all satellites, so a GPS receiver has only to listen to one satellite
in order to know which satellites are "visible" (in the sky) at that particular
time. Almanac data is good for about six months, so when you turn the
receiver off, then back on a month later, it will know what satellites to look
for.
Ephemeris data is very precise data which each satellite transmits to tell
the GPS receiver exactly where it is and what its orbital parameters will be
for about the next four hours. Each satellite transmits its own unique
ephemeris data.

GPS SYSTEM SEGMENTS

The GPS system is composed of three segments: the Space Segment,
the Control Segment, and the User Segment.
The Space Segment consists of the 24 NAVSTAR satellites which orbit
the earth at an altitude of 10,898 nautical miles. The satellite orbits are
very precisely planned so that the entire surface of the earth may use the
GPS system 24 hours a day, every day. There are almost always more
than six satellites in view from anywhere on Earth.
The Control Segment consists of a network of ground-based monitoring
and control stations. The Master Control Station is located in Colorado
Springs, Colorado. All satellite data which is collected by the other ground
stations is assimilated and analyzed at Colorado Springs. Based on these
analyses, ephemeris updates (such as system clock corrections) are sent
(uplinked) to the satellites through radio transmitters at the ground sta-
tions. These ground stations are located at Kwajalein (west of Hawaii in
the central Pacific Ocean), Diego Garcia (in the Indian Ocean), and
Ascension (in the south Atlantic Ocean).
As an owner of a GPS system, you can now claim to be a certified mem-
ber of the GPS User Segment! GPS has many users and uses, and more
are being dreamed up all the time. Not only are aircraft using GPS navi-
gation, so are military systems and personnel, boaters, hikers, and
surveyors. Personal automobiles and transport trucks use Intelligent
Transportation Systems, or ITS, to find their destinations, and track their
movements. Some biologists attach GPS receivers to animals to monitor
their movement and migration patterns. Geologists even use GPS to
track the movement of glaciers and to analyze plate tectonics (movements
of the Earth's crust).
F-2

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