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CHAPTER 7
Satellite Navigation
The concept of using satellites for navigation dates back to Sputnik 1 in
1958 when engineers monitoring this first orbiting body observed that the
substantial Doppler frequency shift of the received telemetry signal could
be used to determine accurately the satellite’s position and orbit. It was
quickly shown that the inverse situation was also possible; that if the satel-
lite position (orbit) were known accurately, an observer’s location on the
earth could be determined. After several years of work at the Applied
Physics Laboratory (APL) of Johns Hopkins University, a prototype satel-
lite was developed and launched, and satellite navigation was born.
The first operational systems were part of the Navy Navigation Satel-
lite System known as “Transit.” The system uses the Doppler positioning
method described further in this chapter and requires information gathered
from only a single satellite, over the time of passage overhead, to produce
a fix. The newest generation of navigation satellites are part of the Glob-
al Positioning Satellite (GPS) system. This system uses a pulse ranging
method of positioning and requires four satellites to be in view of the
receiver simultaneously for a complete solution. Though the requirements
are more stringent, GPS provides real-time, three-dimensional position,
track, and speed with accuracies many times better than the earlier Tran-
sit system.
POSITION DETERMINATION USING DOPPLER TECHNIQUES
The original method of determining position from satellite signals is
through observation of the Doppler shift in frequency of a known signal
as the satellite passes over the observation area. The shift in frequency is
a unique function of the motion of the satellite relative to the observer’s
position. To compute an observer’s location accurately, the position and
orbit of the satellite and the frequency of the transmitted signal must be
known. Also, timing between the transmitting satellite and the observer’s
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