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5 X-ray Pulsar-Based Navigation: Theories and Experiments
XPNAV system and realizing the long-term and high-precision autonomous operation of the navigation constellation will play a positive role in promoting national
economic and social development.
The second application field is to realize the autonomous navigation and precise
control for the deep-space exploration and interstellar vehicles. For the navigations
applications to the deep-space probes and interstellar vehicles, as well as to the rovers
on the planetary surface without dense atmosphere, the GNSS is powerless; the TT&C
signal strengths from the ground-based deep-space network decay with the distance,
and the ranging error will increase by 4 km per increasing the measurement distance
of 1 AU; the traditional celestial navigation ways, due to low navigation accuracy,
incomplete navigation information and difficult technical implementation, cannot
meet the requirements of autonomous navigation and precise control for the deepspace exploration and interstellar flight spacecrafts. In other words, with the rapid
development of deep-space exploration and interstellar flight missions, the groundbased deep-space TT&C networks are facing serious challenges and the traditional
navigation ways and their combinations are difficult to meet the requirements of
the autonomous navigation and precise control for the deep-space exploration and
interstellar vehicles. The X-ray pulsars are suitable for the navigation applications in
the whole solar system and interstellar space, and by measuring the arrival-time of the
X-ray photons radiated from the pulsars, the navigation parameters of the deep-space
exploration and interstellar vehicles relative to the SSB can be determined. From the
numerical experiment results in the previous section, it is shown that when the angular
position accuracies of the pulsars are 0.1 milliarcseconds, and the accuracies of the
pulsar timing model, time transformation model and pulse arrival-time measurement
are 100 ns, respectively, the orbit determination and time parameters can be estimated,
respectively, with the accuracy levels of 10 m and 1 ns, and the attitude estimation
accuracy is better than 21 arc-seconds. So, using the X-ray signals radiated from
the pulsars as natural beacons, the deep-space exploration and interstellar vehicles
can achieve the autonomous navigation and precise control under the large-scale
space-time reference frame.
The third application field is to construct the unified space-ground pulsar time
system. The TAI is maintained together by the atomic clock groups distributed over
the global time laboratories. The long-term instability of the TAI has been detected
by using the pulsar timescale established by the ground radio pulsar observation
network. The advantage of the pulsar timescale is with the long-term time stability
of better than 10
−19 s/s, which is higher than that of the most stable hydrogen atomic
clock at present. By observing the X-ray signals radiated from the pulsars on the
space-based platform and the radio signals radiated by the same pulsars with the
ground-based radio telescopes, a long-term stable pulsar time reference system would
be constructed to serve the national defense, scientific research and national economic
development.
The fourth application field is to promote the interdisciplinary and basic science
developments. The X-ray detections have always been the research fields of astrophysics, particle physics and astrometry, so the studies on the XPNAV and X-ray
detection technology can not only be used in the field of spacecraft’s autonomous
5 X-ray Pulsar-Based Navigation: Theories and Experiments
XPNAV system and realizing the long-term and high-precision autonomous operation of the navigation constellation will play a positive role in promoting national
economic and social development.
The second application field is to realize the autonomous navigation and precise
control for the deep-space exploration and interstellar vehicles. For the navigations
applications to the deep-space probes and interstellar vehicles, as well as to the rovers
on the planetary surface without dense atmosphere, the GNSS is powerless; the TT&C
signal strengths from the ground-based deep-space network decay with the distance,
and the ranging error will increase by 4 km per increasing the measurement distance
of 1 AU; the traditional celestial navigation ways, due to low navigation accuracy,
incomplete navigation information and difficult technical implementation, cannot
meet the requirements of autonomous navigation and precise control for the deepspace exploration and interstellar flight spacecrafts. In other words, with the rapid
development of deep-space exploration and interstellar flight missions, the groundbased deep-space TT&C networks are facing serious challenges and the traditional
navigation ways and their combinations are difficult to meet the requirements of
the autonomous navigation and precise control for the deep-space exploration and
interstellar vehicles. The X-ray pulsars are suitable for the navigation applications in
the whole solar system and interstellar space, and by measuring the arrival-time of the
X-ray photons radiated from the pulsars, the navigation parameters of the deep-space
exploration and interstellar vehicles relative to the SSB can be determined. From the
numerical experiment results in the previous section, it is shown that when the angular
position accuracies of the pulsars are 0.1 milliarcseconds, and the accuracies of the
pulsar timing model, time transformation model and pulse arrival-time measurement
are 100 ns, respectively, the orbit determination and time parameters can be estimated,
respectively, with the accuracy levels of 10 m and 1 ns, and the attitude estimation
accuracy is better than 21 arc-seconds. So, using the X-ray signals radiated from
the pulsars as natural beacons, the deep-space exploration and interstellar vehicles
can achieve the autonomous navigation and precise control under the large-scale
space-time reference frame.
The third application field is to construct the unified space-ground pulsar time
system. The TAI is maintained together by the atomic clock groups distributed over
the global time laboratories. The long-term instability of the TAI has been detected
by using the pulsar timescale established by the ground radio pulsar observation
network. The advantage of the pulsar timescale is with the long-term time stability
of better than 10
−19 s/s, which is higher than that of the most stable hydrogen atomic
clock at present. By observing the X-ray signals radiated from the pulsars on the
space-based platform and the radio signals radiated by the same pulsars with the
ground-based radio telescopes, a long-term stable pulsar time reference system would
be constructed to serve the national defense, scientific research and national economic
development.
The fourth application field is to promote the interdisciplinary and basic science
developments. The X-ray detections have always been the research fields of astrophysics, particle physics and astrometry, so the studies on the XPNAV and X-ray
detection technology can not only be used in the field of spacecraft’s autonomous