Global Positioning System Reference
In-Depth Information
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C
HAPTER 3
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S
ATELLITE SYSTEMS
Lin
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*
3
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No
*PgE
Satellite motions are introduced by means of normal orbits and the derivation and dis-
cussion of the three Kepler laws. A summary of the major effects that cause orbital
perturbed motions follows. The description of the global positioning system (GPS)
takes up most of this chapter. A brief summary of GPS modernization is offered. The
chapter concludes with a description of GLONASS and the forthcoming Galileo sys-
tem. Readers interested in signal processing inside receivers are encouraged to consult
the excellent references Kaplan (1986), Misra and Enge (2001), and Parkinson et al.
(1996).
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3.1 MOTION OF SATELLITES
The orbital motion of a satellite is a result of the earth's gravitational attraction, as
well as a number of other forces acting on the satellite. The attraction of the sun and
the moon and the pressure on the satellite caused by impacting solar radiation parti-
cles are examples of these forces. For high-orbiting satellites, the atmospheric drag
is negligible. Mathematically, the equations of motion for satellites are differential
equations that are solved by numerical integration over time. The integration begins
with initial conditions, such as the position and velocity of the satellite at some ini-
tial epoch. The computed (predicted) satellite positions can be compared with actual
observations. Possible discrepancies are useful to improve the force function or the
station position of the observer.
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