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5 X-ray Pulsar-Based Navigation: Theories and Experiments
orbit determination accuracy of 10 m, time synchronization accuracy of 1 ns and
attitude determination accuracy of 3 arc-seconds, so as to meet the requirements of
high-precision autonomous navigation for the future spacecrafts from the near-earth
orbit to deep space, interstellar space.
By 2030, the orbit determination accuracy of deep-space probes of the NASA
will be required to reach the order of 100 m. However, it is difficult to meet the
navigation accuracy requirements for the deep-space exploration missions by using
the ground deep space TT&C network or traditional celestial navigation methods.
For this reason, a research program of deep-space navigation technology using Xray pulsars was initiated by the NASA in February 2006. The general contractor
of this program was the Microcosm Inc., in cooperation with the ASTER Labs Inc.,
CrossTrac Engineering Inc., NRL and Goddard Space Flight Center (GSFC), to carry
out the related research work [15–17].
In 2009, on the basis of the XNAV Program, X-ray Timing (XTIM) Program
was also funded by the DARPA. The XTIM was led by Lockheed Martin Corporation, cooperated with Ball Aerospace & Technologies Corporation, to together
develop a large-area array collimation detector and finally build an independent and
stable space-ground pulsar timing reference system. In 2011, the GSFC together with
the U.S. Universities Space Research Association (USRA) proposed a technology
demonstration enhancement mission of “Neutron star Interior Composition Explorer
(NICER)”, called “Station Experiment for X-ray Timing and Navigation Technology
(SEXTANT)”. The NICER is an International Space Station (ISS) payload devoted to
the study on neutron stars through soft X-ray timing, and its scientific objectives are
to resolve the nature of ultra-dense matter at the threshold of collapse to black hole
and to reveal the interior composition, dynamic processes and radiation mechanisms
of neutron stars. The SEXTANT is to demonstrate the feasibility of XNAV in real
time through the sequential observation of multiple millisecond pulsars, which is an
important milestone for the technical enhancement test of the NICER mission. The
SEXTANT system is composed of four parts, including X-ray Timing Instrument
(XTI), in-orbit flight software, ground data support and ground test bed [18–20].
The XTI as the core device of the NICER represents an innovative configuration of
high-heritage components, and its heart is an aligned collection array of 56 X-ray
concentrator optics and Silicon Drift Detector (SDD) pairs. Each of the X-ray concentrator optics collects X-rays over a large geometric area from a roughly 30 square
arc-minutes region of the sky and focuses them onto a small SDD. The XTI is a cubic
shape, with the volume of 778 mm × 1245 mm × 800 mm, the detection energy
spectrum range of 0.2−12 keV, the effective detection area of more than 2000 cm
2 at
1.5 keV and 600 cm
2 at 6 keV, the energy resolution of 85 eV at 1 keV and 137 eV at
6 keV and the time-tagging resolution of less than 300 ns. In June 2017, the NICER
was launched to the ISS by a SpaceX Falcon-9 rocket, to carry out the experiments
of X-ray astronomy and the tests of SEXTANT, where a flight navigation experiment
was conducted in November 2017, with an initial orbit determination accuracy of
better than 10 km [21].
5 X-ray Pulsar-Based Navigation: Theories and Experiments
orbit determination accuracy of 10 m, time synchronization accuracy of 1 ns and
attitude determination accuracy of 3 arc-seconds, so as to meet the requirements of
high-precision autonomous navigation for the future spacecrafts from the near-earth
orbit to deep space, interstellar space.
By 2030, the orbit determination accuracy of deep-space probes of the NASA
will be required to reach the order of 100 m. However, it is difficult to meet the
navigation accuracy requirements for the deep-space exploration missions by using
the ground deep space TT&C network or traditional celestial navigation methods.
For this reason, a research program of deep-space navigation technology using Xray pulsars was initiated by the NASA in February 2006. The general contractor
of this program was the Microcosm Inc., in cooperation with the ASTER Labs Inc.,
CrossTrac Engineering Inc., NRL and Goddard Space Flight Center (GSFC), to carry
out the related research work [15–17].
In 2009, on the basis of the XNAV Program, X-ray Timing (XTIM) Program
was also funded by the DARPA. The XTIM was led by Lockheed Martin Corporation, cooperated with Ball Aerospace & Technologies Corporation, to together
develop a large-area array collimation detector and finally build an independent and
stable space-ground pulsar timing reference system. In 2011, the GSFC together with
the U.S. Universities Space Research Association (USRA) proposed a technology
demonstration enhancement mission of “Neutron star Interior Composition Explorer
(NICER)”, called “Station Experiment for X-ray Timing and Navigation Technology
(SEXTANT)”. The NICER is an International Space Station (ISS) payload devoted to
the study on neutron stars through soft X-ray timing, and its scientific objectives are
to resolve the nature of ultra-dense matter at the threshold of collapse to black hole
and to reveal the interior composition, dynamic processes and radiation mechanisms
of neutron stars. The SEXTANT is to demonstrate the feasibility of XNAV in real
time through the sequential observation of multiple millisecond pulsars, which is an
important milestone for the technical enhancement test of the NICER mission. The
SEXTANT system is composed of four parts, including X-ray Timing Instrument
(XTI), in-orbit flight software, ground data support and ground test bed [18–20].
The XTI as the core device of the NICER represents an innovative configuration of
high-heritage components, and its heart is an aligned collection array of 56 X-ray
concentrator optics and Silicon Drift Detector (SDD) pairs. Each of the X-ray concentrator optics collects X-rays over a large geometric area from a roughly 30 square
arc-minutes region of the sky and focuses them onto a small SDD. The XTI is a cubic
shape, with the volume of 778 mm × 1245 mm × 800 mm, the detection energy
spectrum range of 0.2−12 keV, the effective detection area of more than 2000 cm
2 at
1.5 keV and 600 cm
2 at 6 keV, the energy resolution of 85 eV at 1 keV and 137 eV at
6 keV and the time-tagging resolution of less than 300 ns. In June 2017, the NICER
was launched to the ISS by a SpaceX Falcon-9 rocket, to carry out the experiments
of X-ray astronomy and the tests of SEXTANT, where a flight navigation experiment
was conducted in November 2017, with an initial orbit determination accuracy of
better than 10 km [21].