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5 X-ray Pulsar-Based Navigation: Theories and Experiments
used as the geometric constraint to correct the orbit. According to the ideal of algorithm, the intersection between the satellite’s orbit and the normal plane is defined
as control point. Between two control points, the orbit parameters of the satellite are
propagated by using the model of orbital mechanics, and at the control points, the
satellite’s orbits are corrected by using the pulse arrival-time ranging observables, to
constrain the satellite’s position within the normal plane. As a result, the positions
of propagating the satellite’s orbits can be corrected to the control points.
Supposed that the GNSS is unable to provide orbit determination services for the
XPNAV-1 at a certain time, and then the satellite’s orbit determination is achieved
by completely relying on the X-ray signals radiated from the pulsar and the orbit
propagation model. Although the orbit determination experiment is accomplished
by post-processing, the entire autonomous navigation process for the XPNAV-1 has
been demonstrated realistically in the orbit. The experimental scenario started on
November 20, 2016, and ended on March 15, 2017 with the time span of 85 days.
The results of autonomous orbit determination experiment of the XPNAV-1 using
the Crab pulsar are shown in Fig. 5.42, where the sub-figure (a) is the orbital error
series obtained directly by the orbital mechanics model propagating; the sub-figure
(b) is the identification of the control points, “1” indicates the case with the control
point, and “0” indicates the case that without the control points, the orbit mechanics
model is used for the orbital propagation; sub-figure (c) is the orbital error series
obtained by using the Crab pulsar’s X-ray observation data from the XPNAV-1.
From Fig. 5.42, it can be seen that the orbital errors obtained directly by using
the satellite’s orbit mechanics model for extrapolation have reached 3500 km during
approximate 3 months; for the autonomous orbit determination of the XPNAV-1
satellite using the X-ray observation data of the Crab pulsar, although there are still
the divergences of the orbital errors between two control points, the orbital errors at
the control points can effectively be suppressed, so that the final cumulative maximum
orbit error is only 820 km. Obviously, the accumulated orbit propagation errors of the
XPNAV-1 have been effectively constrained and suppressed as the pulse arrival-time
ranging observables of the Crab pulsar are added to modify the satellite’s orbits. To
further illustrate the effectiveness of the orbit correction using the observation data of
single pulsar, the orbital error series at 25 control-points are shown in Fig. 5.43, from
which it can be seen that the orbital error series at the control points are convergent
completely, with the RMS of 38.4 km. From experimental results, it is shown that
the effectiveness of pulsar navigation is confirmed by using the observation data
from the XPNAV-1 satellite, and the feasibility of the pulsar navigation mechanism
is demonstrated preliminarily by the space flight test.
Launching the XPNAV-1 satellite is only the first step in the space flight test
program of pulsar navigation in China. In the future, a series of dedicated test satellites will be developed and launched to verify the performance of large-area X-ray
detectors, and then the space-based reference constellation for the pulsar navigation
will be constructed. The ultimate goals are to achieve the space-based autonomous
operations and controls for navigation constellations, the autonomous navigations
for deep-space vehicles and the construction of integrated space-ground pulsar time
5 X-ray Pulsar-Based Navigation: Theories and Experiments
used as the geometric constraint to correct the orbit. According to the ideal of algorithm, the intersection between the satellite’s orbit and the normal plane is defined
as control point. Between two control points, the orbit parameters of the satellite are
propagated by using the model of orbital mechanics, and at the control points, the
satellite’s orbits are corrected by using the pulse arrival-time ranging observables, to
constrain the satellite’s position within the normal plane. As a result, the positions
of propagating the satellite’s orbits can be corrected to the control points.
Supposed that the GNSS is unable to provide orbit determination services for the
XPNAV-1 at a certain time, and then the satellite’s orbit determination is achieved
by completely relying on the X-ray signals radiated from the pulsar and the orbit
propagation model. Although the orbit determination experiment is accomplished
by post-processing, the entire autonomous navigation process for the XPNAV-1 has
been demonstrated realistically in the orbit. The experimental scenario started on
November 20, 2016, and ended on March 15, 2017 with the time span of 85 days.
The results of autonomous orbit determination experiment of the XPNAV-1 using
the Crab pulsar are shown in Fig. 5.42, where the sub-figure (a) is the orbital error
series obtained directly by the orbital mechanics model propagating; the sub-figure
(b) is the identification of the control points, “1” indicates the case with the control
point, and “0” indicates the case that without the control points, the orbit mechanics
model is used for the orbital propagation; sub-figure (c) is the orbital error series
obtained by using the Crab pulsar’s X-ray observation data from the XPNAV-1.
From Fig. 5.42, it can be seen that the orbital errors obtained directly by using
the satellite’s orbit mechanics model for extrapolation have reached 3500 km during
approximate 3 months; for the autonomous orbit determination of the XPNAV-1
satellite using the X-ray observation data of the Crab pulsar, although there are still
the divergences of the orbital errors between two control points, the orbital errors at
the control points can effectively be suppressed, so that the final cumulative maximum
orbit error is only 820 km. Obviously, the accumulated orbit propagation errors of the
XPNAV-1 have been effectively constrained and suppressed as the pulse arrival-time
ranging observables of the Crab pulsar are added to modify the satellite’s orbits. To
further illustrate the effectiveness of the orbit correction using the observation data of
single pulsar, the orbital error series at 25 control-points are shown in Fig. 5.43, from
which it can be seen that the orbital error series at the control points are convergent
completely, with the RMS of 38.4 km. From experimental results, it is shown that
the effectiveness of pulsar navigation is confirmed by using the observation data
from the XPNAV-1 satellite, and the feasibility of the pulsar navigation mechanism
is demonstrated preliminarily by the space flight test.
Launching the XPNAV-1 satellite is only the first step in the space flight test
program of pulsar navigation in China. In the future, a series of dedicated test satellites will be developed and launched to verify the performance of large-area X-ray
detectors, and then the space-based reference constellation for the pulsar navigation
will be constructed. The ultimate goals are to achieve the space-based autonomous
operations and controls for navigation constellations, the autonomous navigations
for deep-space vehicles and the construction of integrated space-ground pulsar time