5.7 Design of Ground Test System
365
constructing the test system of the XPNAV, the characteristics of the X-ray photon
signals from the pulsars are simulated to test the function and performance of the
X-ray detectors and verify the principle of the XPNAV system. Obviously, in the technical studies, space flight tests and engineering applications of the XPNAV, it is very
necessary to construct the ground test system facilities, which can provide the closely
realistic environment and detection platform for the pulsar’s signal simulating, key
technology testing, navigation principle verifying, and actual data processing.
(1) Constructing the ground test system is the inevitable requirement for simulating the pulsar’s signals. When the electromagnetic wave passes through the
Earth’s atmosphere, it will be affected by the absorption and scattering of the
atmosphere, so that its energy is attenuated. The effects that the atmosphere
absorbs and scatters electromagnetic wave vary with wavelength. It is well
known that there are only two electromagnetic radiation windows in the dense
atmosphere of the Earth: one is the optical window, and another is the radio
window. Generally, the atmospheric penetration rate of the visible light is more
than 95%, while that of the radio wave is almost 100%. However, the X-rays
emitted by the pulsars are a kind of high-energy electromagnetic wave, which
is not covered by the atmospheric windows. When the X-rays propagate in
the dense atmosphere of the Earth, they will be completely absorbed, so that
the X-ray photon signals radiated from the pulsars cannot be received on the
ground. So, in the vacuum environment of laboratory, constructing the ground
test system, to closely realistically simulate the process of the X-ray photons
radiated from the pulsars, is the precondition that the key technologies of the
XPNAV are studied and verified on the ground.
(2) Constructing the ground test system is the core link to verify the key technologies of the XPNAV. The spacecraft’s autonomous navigation based on the X-ray
pulsars involves many key technologies, such as the X-ray detection, pulsar’s
database construction, time keeping, and large-scale navigation. Facing the
requirements for developing the spacecraft’s autonomous navigation, it is very
necessary to build the ground test system and verify the key technologies of
the XPNAV. In the environment of laboratory, the key technologies, such as the
updating and calling of pulsar navigation data, high-precision transformation
of arrival-time of the photons, X-ray photon detection, autonomous navigation
algorithm and fault-tolerant processing, are tested and verified by using the
ground test system, so as to demonstrate the feasibility of the XPNAV and
provide the technical supports for the space flight tests.
(3) Constructing the ground test system is the important means to test the detectors
of the XPNAV. The function of the detector system of the XPNAV is to detect
the X-ray photons emitted by the pulsars, and accurately record the arrivaltime of the photons using the onboard atomic clock. The X-ray detectors are
made by using the properties of the interaction of the X-rays with the materials. Currently, there are many types of the X-ray detectors, such as the gas
proportional counter, scintillation, micro-channel plate, silicon semiconductor,
charge-coupled device, scanning-charge device and silicon drift device, which
365
constructing the test system of the XPNAV, the characteristics of the X-ray photon
signals from the pulsars are simulated to test the function and performance of the
X-ray detectors and verify the principle of the XPNAV system. Obviously, in the technical studies, space flight tests and engineering applications of the XPNAV, it is very
necessary to construct the ground test system facilities, which can provide the closely
realistic environment and detection platform for the pulsar’s signal simulating, key
technology testing, navigation principle verifying, and actual data processing.
(1) Constructing the ground test system is the inevitable requirement for simulating the pulsar’s signals. When the electromagnetic wave passes through the
Earth’s atmosphere, it will be affected by the absorption and scattering of the
atmosphere, so that its energy is attenuated. The effects that the atmosphere
absorbs and scatters electromagnetic wave vary with wavelength. It is well
known that there are only two electromagnetic radiation windows in the dense
atmosphere of the Earth: one is the optical window, and another is the radio
window. Generally, the atmospheric penetration rate of the visible light is more
than 95%, while that of the radio wave is almost 100%. However, the X-rays
emitted by the pulsars are a kind of high-energy electromagnetic wave, which
is not covered by the atmospheric windows. When the X-rays propagate in
the dense atmosphere of the Earth, they will be completely absorbed, so that
the X-ray photon signals radiated from the pulsars cannot be received on the
ground. So, in the vacuum environment of laboratory, constructing the ground
test system, to closely realistically simulate the process of the X-ray photons
radiated from the pulsars, is the precondition that the key technologies of the
XPNAV are studied and verified on the ground.
(2) Constructing the ground test system is the core link to verify the key technologies of the XPNAV. The spacecraft’s autonomous navigation based on the X-ray
pulsars involves many key technologies, such as the X-ray detection, pulsar’s
database construction, time keeping, and large-scale navigation. Facing the
requirements for developing the spacecraft’s autonomous navigation, it is very
necessary to build the ground test system and verify the key technologies of
the XPNAV. In the environment of laboratory, the key technologies, such as the
updating and calling of pulsar navigation data, high-precision transformation
of arrival-time of the photons, X-ray photon detection, autonomous navigation
algorithm and fault-tolerant processing, are tested and verified by using the
ground test system, so as to demonstrate the feasibility of the XPNAV and
provide the technical supports for the space flight tests.
(3) Constructing the ground test system is the important means to test the detectors
of the XPNAV. The function of the detector system of the XPNAV is to detect
the X-ray photons emitted by the pulsars, and accurately record the arrivaltime of the photons using the onboard atomic clock. The X-ray detectors are
made by using the properties of the interaction of the X-rays with the materials. Currently, there are many types of the X-ray detectors, such as the gas
proportional counter, scintillation, micro-channel plate, silicon semiconductor,
charge-coupled device, scanning-charge device and silicon drift device, which