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5 X-ray Pulsar-Based Navigation: Theories and Experiments
5.1 Principle of Pulsar Navigation
Generally, the center of mass of solar system, also called the Solar System’s
Barycenter (SSB), is selected as a space-time reference point for the XPNAV. The
SSB is the center of mass of the whole solar system, which is the most stable point
in the solar system, located near the Sun’s surface and on the side of the Jupiter,
and the Sun and its planets move around this point. The SSB is constantly shifting
since the planets are always in motion. The positions of the planets determine those
of the barycenter. The pulse profile and its pulse Time of Arrival (TOA) of a pulsar
relative to the SSB can be accurately measured and predicted. Therefore, the mathematical models and basic observables of the XPNAV are usually expressed in the
SSB coordinate system.
With the SSB as the coordinate origin O SSB , and the X SSB -axis pointing to the
vernal equinox defined by the J2000.0 reference epoch, the SSB coordinate system
O SSB −X SSB Y SSB Z SSB can be established in the equatorial plane of the celestial sphere,
as shown in Fig. 5.1, where PSR, SC, O E and O S , respectively, denote the pulsar,
spacecraft, Earth’s center of mass and Sun’s center of mass; λ and α, respectively,
Fig. 5.1 Geometric Principle of XPNAV
5 X-ray Pulsar-Based Navigation: Theories and Experiments
5.1 Principle of Pulsar Navigation
Generally, the center of mass of solar system, also called the Solar System’s
Barycenter (SSB), is selected as a space-time reference point for the XPNAV. The
SSB is the center of mass of the whole solar system, which is the most stable point
in the solar system, located near the Sun’s surface and on the side of the Jupiter,
and the Sun and its planets move around this point. The SSB is constantly shifting
since the planets are always in motion. The positions of the planets determine those
of the barycenter. The pulse profile and its pulse Time of Arrival (TOA) of a pulsar
relative to the SSB can be accurately measured and predicted. Therefore, the mathematical models and basic observables of the XPNAV are usually expressed in the
SSB coordinate system.
With the SSB as the coordinate origin O SSB , and the X SSB -axis pointing to the
vernal equinox defined by the J2000.0 reference epoch, the SSB coordinate system
O SSB −X SSB Y SSB Z SSB can be established in the equatorial plane of the celestial sphere,
as shown in Fig. 5.1, where PSR, SC, O E and O S , respectively, denote the pulsar,
spacecraft, Earth’s center of mass and Sun’s center of mass; λ and α, respectively,
Fig. 5.1 Geometric Principle of XPNAV