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5 X-ray Pulsar-Based Navigation: Theories and Experiments
the master control station, and is compared with the UTC times maintained by the
Italian National Institute of Metrological Research (IT), the British National Physical Laboratory (NPL), the French National Metrology and Testing Laboratory (OP)
and the Federal Physical Institute of Germany (PTB), to correct the time from the
hydrogen atomic clocks. The GST is similar to the GPST, also a continuous timing
system, with the timescale of the TAI, and its daily stability is better than 4.3 × 10
−15
s/s relative to the TAI, with the time bias of less than 28 ns.
5.3.3 International Terrestrial Reference System and Its
Realization
The terrestrial reference system is a non-inertial coordinate system which is fixed on
the Earth, rotating together with the Earth. If the Earth is an ideal rigid body, any threeaxis coordinate system fixed on the Earth is suitable, and the choice of the terrestrial
reference system only depends on the convenience of the ground observation station.
However, the Earth is a discontinuous deformation body, and due to the coupling
motions among various Earth spheres and the polar wander, it is complicated to fix
the reference system in the Earth using the ideal way. The ideal terrestrial reference
system is a kind of reference system which only has deformation, no whole rotation
and translation relative to the Earth, while relative to the inertial reference system,
only contains the whole motion of the Earth (i.e., the rotation and revolution of
the Earth). For the ideal terrestrial reference system, besides defining its fixed way
relative to the Earth, its coordinate origin, scale and orientation must also be defined
in practical application. Therefore, the establishment of geocentric coordinate system
should meet the following four basic conditions:
(1) The coordinate origin is located at the center of mass of the whole Earth,
including the solid Earth, ocean and atmosphere.
(2) The coordinate scale is the scale within a local terrestrial frame based on the
general relativity (seen in Sect. 5.4).
(3) The orientation parameters are determined by the Earth rotation parameters at
an epoch. For example, the Conventional Terrestrial Pole (CTP) and the zero
meridian line are determined at an epoch by the BIH. The Z-axis and X-axis in
the BIH 1984.0 coordinate system are, respectively, the CTP and Zero Meridian
determined at the 1984.0 epoch by the BIH.
(4) The orientating evolution over time is subject to the constraint that there are
not the whole rotation and translation relative to the Earth.
Generally, the physical frame composed of a series of observation stations on
the Earth’s surface is the best approximate and concrete form of the ideal terrestrial
reference system, and its motion and deformation must meet the demand that there
are not the whole rotation and translation relative to the Earth. On the basis of
selecting the physical frame, the parameters and models to describe the frame need
to be determined. The purpose of establishing the physical frame model based on the
5 X-ray Pulsar-Based Navigation: Theories and Experiments
the master control station, and is compared with the UTC times maintained by the
Italian National Institute of Metrological Research (IT), the British National Physical Laboratory (NPL), the French National Metrology and Testing Laboratory (OP)
and the Federal Physical Institute of Germany (PTB), to correct the time from the
hydrogen atomic clocks. The GST is similar to the GPST, also a continuous timing
system, with the timescale of the TAI, and its daily stability is better than 4.3 × 10
−15
s/s relative to the TAI, with the time bias of less than 28 ns.
5.3.3 International Terrestrial Reference System and Its
Realization
The terrestrial reference system is a non-inertial coordinate system which is fixed on
the Earth, rotating together with the Earth. If the Earth is an ideal rigid body, any threeaxis coordinate system fixed on the Earth is suitable, and the choice of the terrestrial
reference system only depends on the convenience of the ground observation station.
However, the Earth is a discontinuous deformation body, and due to the coupling
motions among various Earth spheres and the polar wander, it is complicated to fix
the reference system in the Earth using the ideal way. The ideal terrestrial reference
system is a kind of reference system which only has deformation, no whole rotation
and translation relative to the Earth, while relative to the inertial reference system,
only contains the whole motion of the Earth (i.e., the rotation and revolution of
the Earth). For the ideal terrestrial reference system, besides defining its fixed way
relative to the Earth, its coordinate origin, scale and orientation must also be defined
in practical application. Therefore, the establishment of geocentric coordinate system
should meet the following four basic conditions:
(1) The coordinate origin is located at the center of mass of the whole Earth,
including the solid Earth, ocean and atmosphere.
(2) The coordinate scale is the scale within a local terrestrial frame based on the
general relativity (seen in Sect. 5.4).
(3) The orientation parameters are determined by the Earth rotation parameters at
an epoch. For example, the Conventional Terrestrial Pole (CTP) and the zero
meridian line are determined at an epoch by the BIH. The Z-axis and X-axis in
the BIH 1984.0 coordinate system are, respectively, the CTP and Zero Meridian
determined at the 1984.0 epoch by the BIH.
(4) The orientating evolution over time is subject to the constraint that there are
not the whole rotation and translation relative to the Earth.
Generally, the physical frame composed of a series of observation stations on
the Earth’s surface is the best approximate and concrete form of the ideal terrestrial
reference system, and its motion and deformation must meet the demand that there
are not the whole rotation and translation relative to the Earth. On the basis of
selecting the physical frame, the parameters and models to describe the frame need
to be determined. The purpose of establishing the physical frame model based on the