278
5 X-ray Pulsar-Based Navigation: Theories and Experiments
area of less than 1 square meter, so as to make it possible that the spacecrafts carry
the detection devices to observe the X-ray pulsars for navigation application.
In 1993, based on the traditional celestial navigation method that is the Earth’s
atmosphere occultation method, a comprehensive test project, called Unconventional
Stellar Aspect experiment (USA), was proposed by Kent S. Wood working at the
U.S. NRL [7–9]. The USA project was a part of the “X-ray Astronomy Program” of
the NRL, and the Stanford Linear Accelerator Center was responsible for the thermal
control design, equipment development and test assembly of the USA. A doctoral
student at the University of Stanford, John E. Hanson, had done a lot of research
work on the USA project and proposed a design scheme of spacecraft’s attitude
measurement and time-keeping phase-locked loop by using the X-ray sources from
celestial bodies, including X-ray pulsars. From his numerical analysis results, it is
shown that the attitude determination accuracy for the spacecrafts reaches 0.01°
and the time-keeping accuracy is better than 1.5 ms [10]. In February 1999, the
Advanced Research and Global Observation Satellite (ARGOS) developed by the
U.S. Air Force, carrying the USA experimental devices, was launched into the solar
synchronous orbit with an orbital altitude of 840 km and an inclination of 98°, to carry
out a total of nine space-science experiments including the USA. A large amount of
test data were gotten by using the X-ray detection devices of the USA experiment
and used to study four special subjects: X-ray astrophysics; X-ray navigation; X-ray
detection on the upper atmosphere of the Earth; advanced signal and data processing
technology under space environment. In the USA experiments, two sets of doubleaxis gimbaled collimated gas proportional counters were used, with the detection
energy spectrum range of 1−15 keV, the effective detection area of 0.1 m
2 and the
Field of View (FOV) of 1.2° by 1.2°. In November 2000, due to the counter’s inert
gas mixture leaking, the USA experiments had to be terminated. It should be pointed
out that the spacecraft’s navigation using the X-ray sources in the USA experiments
is a traditional celestial navigation method based on the atmospheric occultation,
so the orbit determination accuracy of the ARGOS mainly depends on the upper
atmosphere model, and is typically the level of tens of kilometers. In other words,
the way of pulse arrival-time ranging had not been adopted in the USA experiments,
so the experiments are not the space flight tests of pulsar navigation in real sense.
In 2004, based on the intensive studies on the physical characteristics of pulsars
and the passive navigation mechanism of one-way arrival-time ranging used in the
GNSS, Suneel I. Sheikh who was then a doctoral student at the University of Maryland theoretically demonstrated the feasibility of the autonomous navigation for
spacecrafts using the X-ray pulsars [11, 12]. In addition, taking the time difference
that the same X-ray signals radiated from pulsars arrive respectively at two GPS satellites, as aiding observables, Dennis W. Woodfork who was then a graduate student
at the U.S. Air Force Institute of Technology studied the method improving the estimation accuracies of the orbit and clock parameters of the GPS satellites. From his
numerical experimental results, it was shown that the accuracies of estimating the
GPS satellite’s orbit and clock parameters could be improved by 30.8% and 21.4%,
respectively, by adding the measurement data of the pulse arrival-time difference
compared with the inter-satellite cross-link pseudoranges used alone [13].
5 X-ray Pulsar-Based Navigation: Theories and Experiments
area of less than 1 square meter, so as to make it possible that the spacecrafts carry
the detection devices to observe the X-ray pulsars for navigation application.
In 1993, based on the traditional celestial navigation method that is the Earth’s
atmosphere occultation method, a comprehensive test project, called Unconventional
Stellar Aspect experiment (USA), was proposed by Kent S. Wood working at the
U.S. NRL [7–9]. The USA project was a part of the “X-ray Astronomy Program” of
the NRL, and the Stanford Linear Accelerator Center was responsible for the thermal
control design, equipment development and test assembly of the USA. A doctoral
student at the University of Stanford, John E. Hanson, had done a lot of research
work on the USA project and proposed a design scheme of spacecraft’s attitude
measurement and time-keeping phase-locked loop by using the X-ray sources from
celestial bodies, including X-ray pulsars. From his numerical analysis results, it is
shown that the attitude determination accuracy for the spacecrafts reaches 0.01°
and the time-keeping accuracy is better than 1.5 ms [10]. In February 1999, the
Advanced Research and Global Observation Satellite (ARGOS) developed by the
U.S. Air Force, carrying the USA experimental devices, was launched into the solar
synchronous orbit with an orbital altitude of 840 km and an inclination of 98°, to carry
out a total of nine space-science experiments including the USA. A large amount of
test data were gotten by using the X-ray detection devices of the USA experiment
and used to study four special subjects: X-ray astrophysics; X-ray navigation; X-ray
detection on the upper atmosphere of the Earth; advanced signal and data processing
technology under space environment. In the USA experiments, two sets of doubleaxis gimbaled collimated gas proportional counters were used, with the detection
energy spectrum range of 1−15 keV, the effective detection area of 0.1 m
2 and the
Field of View (FOV) of 1.2° by 1.2°. In November 2000, due to the counter’s inert
gas mixture leaking, the USA experiments had to be terminated. It should be pointed
out that the spacecraft’s navigation using the X-ray sources in the USA experiments
is a traditional celestial navigation method based on the atmospheric occultation,
so the orbit determination accuracy of the ARGOS mainly depends on the upper
atmosphere model, and is typically the level of tens of kilometers. In other words,
the way of pulse arrival-time ranging had not been adopted in the USA experiments,
so the experiments are not the space flight tests of pulsar navigation in real sense.
In 2004, based on the intensive studies on the physical characteristics of pulsars
and the passive navigation mechanism of one-way arrival-time ranging used in the
GNSS, Suneel I. Sheikh who was then a doctoral student at the University of Maryland theoretically demonstrated the feasibility of the autonomous navigation for
spacecrafts using the X-ray pulsars [11, 12]. In addition, taking the time difference
that the same X-ray signals radiated from pulsars arrive respectively at two GPS satellites, as aiding observables, Dennis W. Woodfork who was then a graduate student
at the U.S. Air Force Institute of Technology studied the method improving the estimation accuracies of the orbit and clock parameters of the GPS satellites. From his
numerical experimental results, it was shown that the accuracies of estimating the
GPS satellite’s orbit and clock parameters could be improved by 30.8% and 21.4%,
respectively, by adding the measurement data of the pulse arrival-time difference
compared with the inter-satellite cross-link pseudoranges used alone [13].