4.6 Navigation Satellite System
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4.6 Navigation Satellite System
The traditional land-based radio navigation system has many disadvantages, such
as limited signal coverage area, outdated equipment, backward technology and low
positioning accuracy (generally the order of several kilometers), so that it is difficult to
meet the requirements for highly precise, highly dynamic and real-time navigations,
including the navigations for land vehicles, ships, aircrafts and spacecrafts. In the late
1950s, human beings entered a new era of exploration, development and utilization
of space, bringing vitality and power to the traditional radio navigation system. The
ground-based radio navigation station equipment is installed on the satellites, and
the satellites are used as the dynamic known points. By receiving the signals from
the satellites, the movable objects can get the basic observables like distances and
Doppler shifts, and thus the navigation parameters including position, velocity and
time can be solved in real time. Generally, the kind of space-based radio positioning,
navigating and time-transferring system is called navigation satellite system. The
navigation satellite system is a space infrastructure for real-time acquisition of highprecision navigation information, which can provide all-weather, full-time, highprecision navigation parameters for the users on the Earth’s surface and in near-earth
space. It has extremely important value for civil and military uses, and has attracted
the attention of all aerospace institutions in the world.
4.6.1 Origin of Navigation Satellite Idea
In 1951, two young physics graduates, George C. Weiffenbach (1921−2003) and
Willian H. Guier (1926−2011), came to work at the Research Center of the Applied
Physics Laboratory (APL), Johns Hopkins University. Both were members of the
Research Centergroup, whose assignment was to apply basic mathematics and
physics method to tasking problems of the Laboratory. In those early days, their
task was to investigate the methods of signal processing to improve the beam rider
performance of Terrier and Talos missiles for defense of the Fleets against air attacks,
especially by enemy planes at very low altitude. This problem was referred to as the
low-angle problem and was of particular concern then.
On October 4, 1957, the world’s first artificial Earth satellite, Sputink-1, was
successfully launched by the USSR. The Sputink-1 was equipped with two radio
transmitters, which broadcasted radio signals to the world at the frequencies
20.005 MHz and 40.002 MHz, respectively. Its purpose is to publicize the Soviet
launch of the first satellite, and its implication for the International Geophysical Year.
Fortunately, Weiffenbach had a good 20-MHz receiver, and there was the National
Bureau of Standards radio stations WWV (a shortwave radio station), only 19.3
kmaway from the APL. The WWV broadcasted the best available frequency and
time standards, and it was so close from the APL that a 0.6-m wire hanging from the
receiver was an adequate antenna. Therefore, the receiver tuned to 20 MHz using the
223
4.6 Navigation Satellite System
The traditional land-based radio navigation system has many disadvantages, such
as limited signal coverage area, outdated equipment, backward technology and low
positioning accuracy (generally the order of several kilometers), so that it is difficult to
meet the requirements for highly precise, highly dynamic and real-time navigations,
including the navigations for land vehicles, ships, aircrafts and spacecrafts. In the late
1950s, human beings entered a new era of exploration, development and utilization
of space, bringing vitality and power to the traditional radio navigation system. The
ground-based radio navigation station equipment is installed on the satellites, and
the satellites are used as the dynamic known points. By receiving the signals from
the satellites, the movable objects can get the basic observables like distances and
Doppler shifts, and thus the navigation parameters including position, velocity and
time can be solved in real time. Generally, the kind of space-based radio positioning,
navigating and time-transferring system is called navigation satellite system. The
navigation satellite system is a space infrastructure for real-time acquisition of highprecision navigation information, which can provide all-weather, full-time, highprecision navigation parameters for the users on the Earth’s surface and in near-earth
space. It has extremely important value for civil and military uses, and has attracted
the attention of all aerospace institutions in the world.
4.6.1 Origin of Navigation Satellite Idea
In 1951, two young physics graduates, George C. Weiffenbach (1921−2003) and
Willian H. Guier (1926−2011), came to work at the Research Center of the Applied
Physics Laboratory (APL), Johns Hopkins University. Both were members of the
Research Centergroup, whose assignment was to apply basic mathematics and
physics method to tasking problems of the Laboratory. In those early days, their
task was to investigate the methods of signal processing to improve the beam rider
performance of Terrier and Talos missiles for defense of the Fleets against air attacks,
especially by enemy planes at very low altitude. This problem was referred to as the
low-angle problem and was of particular concern then.
On October 4, 1957, the world’s first artificial Earth satellite, Sputink-1, was
successfully launched by the USSR. The Sputink-1 was equipped with two radio
transmitters, which broadcasted radio signals to the world at the frequencies
20.005 MHz and 40.002 MHz, respectively. Its purpose is to publicize the Soviet
launch of the first satellite, and its implication for the International Geophysical Year.
Fortunately, Weiffenbach had a good 20-MHz receiver, and there was the National
Bureau of Standards radio stations WWV (a shortwave radio station), only 19.3
kmaway from the APL. The WWV broadcasted the best available frequency and
time standards, and it was so close from the APL that a 0.6-m wire hanging from the
receiver was an adequate antenna. Therefore, the receiver tuned to 20 MHz using the