4.2 From Ancient South-Pointing Chariot to Modern Navigation System
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described sequentially in the following of this chapter. In addition, the pulsar navigation system, which uses the X-rays radiated by pulsars as natural beacons to provide
long-time and high-precision autonomous navigation information for all kinds of
spacecrafts, will be discussed in detail in Chap. 5 of this book, and thus the pulsars
are known as the lighthouses for space flights. The other navigation technologies,
such as the terrain matching navigation, the navigation based on the Earth’s magnetic
field, the gravity matching navigation and the navigation based on the biological
polarized skylight [5, 6], are still in the phase of theoretical exploration, and thereby
they will not be involved in this book.
4.3 Celestial Navigation System
4.3.1 Basic Principle
The Celestial Navigation System (CNS) is a system in which the movable object
used its own celestial observation equipment to measure the elevation angles and
azimuth angles of celestial bodies, such as the Sun, Moon, planets and stars, determine
its position and attitude, and guide itself to safely voyage according to the scheduled
plans and requirements. Its basic principle is: in local geographical coordinate system,
both heading angle and elevation angle are measured by the star-observed devices,
of which the former is the angle, on the local horizontal plane, between the direction
of celestial body and the motion direction of movable object, and the latter is the angle
between the direction of celestial body and the local horizon; the real heading of the
movable object can be obtained by the azimuth angle of the celestial body looked up
from the star almanacs at the corresponding epoch, subtracting the heading angle;
the complementary angle of the elevation angle is called zenith distance, and the
point that the celestial body is projected on the surface of the Earth is called star
point; thereby, a circle with the star point as the circular center, and the spherical
distance corresponding to the zenith distance on the Earth’s surface as the radius
can be drawn, and called circle of equal altitude; two circles of equal altitude are
obtained by simultaneously observing two celestial bodies, and the intersections of
the two circles form the real and false positions of the movable object; finally, with
the prior information of the movable object’s position or with the third equal-altitude
circle, the false position can be eliminated, so that the longitude and latitude of the
movable object can be solved, as shown in Fig. 4.1. In general, the CNS consists of the
star-observed device, time generator, star-chart database and navigation computer.
The star-observed devices usually include star tracker, celestial compass and sextant.
The star tracker (also known as star sensor) is used to search, identify and track the
celestial bodies in the background sky, and to measure the angle of the star tracker’s
aiming line direction relative to reference coordinate system. The celestial compass
can indicate the heading direction of the movable object by measuring the direction
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described sequentially in the following of this chapter. In addition, the pulsar navigation system, which uses the X-rays radiated by pulsars as natural beacons to provide
long-time and high-precision autonomous navigation information for all kinds of
spacecrafts, will be discussed in detail in Chap. 5 of this book, and thus the pulsars
are known as the lighthouses for space flights. The other navigation technologies,
such as the terrain matching navigation, the navigation based on the Earth’s magnetic
field, the gravity matching navigation and the navigation based on the biological
polarized skylight [5, 6], are still in the phase of theoretical exploration, and thereby
they will not be involved in this book.
4.3 Celestial Navigation System
4.3.1 Basic Principle
The Celestial Navigation System (CNS) is a system in which the movable object
used its own celestial observation equipment to measure the elevation angles and
azimuth angles of celestial bodies, such as the Sun, Moon, planets and stars, determine
its position and attitude, and guide itself to safely voyage according to the scheduled
plans and requirements. Its basic principle is: in local geographical coordinate system,
both heading angle and elevation angle are measured by the star-observed devices,
of which the former is the angle, on the local horizontal plane, between the direction
of celestial body and the motion direction of movable object, and the latter is the angle
between the direction of celestial body and the local horizon; the real heading of the
movable object can be obtained by the azimuth angle of the celestial body looked up
from the star almanacs at the corresponding epoch, subtracting the heading angle;
the complementary angle of the elevation angle is called zenith distance, and the
point that the celestial body is projected on the surface of the Earth is called star
point; thereby, a circle with the star point as the circular center, and the spherical
distance corresponding to the zenith distance on the Earth’s surface as the radius
can be drawn, and called circle of equal altitude; two circles of equal altitude are
obtained by simultaneously observing two celestial bodies, and the intersections of
the two circles form the real and false positions of the movable object; finally, with
the prior information of the movable object’s position or with the third equal-altitude
circle, the false position can be eliminated, so that the longitude and latitude of the
movable object can be solved, as shown in Fig. 4.1. In general, the CNS consists of the
star-observed device, time generator, star-chart database and navigation computer.
The star-observed devices usually include star tracker, celestial compass and sextant.
The star tracker (also known as star sensor) is used to search, identify and track the
celestial bodies in the background sky, and to measure the angle of the star tracker’s
aiming line direction relative to reference coordinate system. The celestial compass
can indicate the heading direction of the movable object by measuring the direction