4.8 Ground Navigation Networks for Spacecrafts
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transmission, data processing, monitoring and display, ground network communication, time reference and auxiliary support [17]. The tracking and measurement
subsystem takes charges of making the TT&C antennas (or telescopes) point to spacecrafts, establishing the space-ground links, getting the spacecrafts’ motion parameters like direction angles, distances and radial velocities, and finally determining the
operational states of spacecrafts. The telemetry subsystem takes charges of receiving
the measurement data from spacecrafts, collecting the data transmitted through the
radio downlinks, storing and processing the data, and finally sending the data to the
ground control center as required. The remote control subsystem takes charges of
forming the injecting commands and data codes, and sending them to the spacecrafts
via the radio uplinks, so as to conduct the real-time control or the program control for
the spacecrafts. The space-ground communication and data transmission subsystem
takes charge of transmitting the voice, message, television, image and special data
between the spacecrafts and the ground TT&C stations, which is mainly used in
manned spaceflights and remote-sensing satellites. The data processing subsystem
takes charges of processing, analyzing and calculating the measurement data, and
forming the injecting commands and data codes, so as to achieve the information
exchange and equipment manage for the TT&C system. The monitoring and display
system takes charges of collecting, processing, classifying and displaying the information sent from the data processing subsystem and concerned by the command
and control personnel, so as to provide the reference basis for analyzing, deciding,
commanding and controlling. The ground network communication subsystem takes
charge of connecting the control center with the TT&C stations, and transmitting the
information such as data, voice and image. The time reference subsystem takes charge
of providing the unified standard time and frequency signals. The auxiliary support
subsystem takes charge of providing the technical supports and logistics services,
such as the meteorological data, geodetic data, power supply and air-conditioning
environment for the control center and TT&C stations; the position, heading and
attitude parameters for the tracking ships; the stable directing beams for the tracking
and measurement antennas; and so on.
Tracking and measuring the orbits and attitudes of spacecrafts have always been
the core tasks of the TT&C system, and thus the tracking and measurement subsystem
is essentially the ground navigation system for spacecrafts, which usually adopts two
kinds of tracking and measuring techniques, optical and radio. For the optical equipment, due to the disadvantages like strict observation condition and limited operating
distance, it is unable to meet the requirements for the spacecraft’s orbit determination
for long-term operation, and thus the optical observations are usually used only in
the stage of launching the spacecrafts into orbits. The radio tracking and measuring
equipment, with the advantages of all-weather, long operating distance, easy information transmission and real-time data processing, usually plays a leading role in
the TT&C system. According to the different working ways, the radio tracking and
measuring equipment can be divided into two types, pulse and continuous wave. The
pulse-type equipment is the measurement radar of transmitting radio-frequency pulse
signals, with the advantages of simple device, as well as single station, single relay
and multi-station working at the same time. The continuous wave-type equipment
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transmission, data processing, monitoring and display, ground network communication, time reference and auxiliary support [17]. The tracking and measurement
subsystem takes charges of making the TT&C antennas (or telescopes) point to spacecrafts, establishing the space-ground links, getting the spacecrafts’ motion parameters like direction angles, distances and radial velocities, and finally determining the
operational states of spacecrafts. The telemetry subsystem takes charges of receiving
the measurement data from spacecrafts, collecting the data transmitted through the
radio downlinks, storing and processing the data, and finally sending the data to the
ground control center as required. The remote control subsystem takes charges of
forming the injecting commands and data codes, and sending them to the spacecrafts
via the radio uplinks, so as to conduct the real-time control or the program control for
the spacecrafts. The space-ground communication and data transmission subsystem
takes charge of transmitting the voice, message, television, image and special data
between the spacecrafts and the ground TT&C stations, which is mainly used in
manned spaceflights and remote-sensing satellites. The data processing subsystem
takes charges of processing, analyzing and calculating the measurement data, and
forming the injecting commands and data codes, so as to achieve the information
exchange and equipment manage for the TT&C system. The monitoring and display
system takes charges of collecting, processing, classifying and displaying the information sent from the data processing subsystem and concerned by the command
and control personnel, so as to provide the reference basis for analyzing, deciding,
commanding and controlling. The ground network communication subsystem takes
charge of connecting the control center with the TT&C stations, and transmitting the
information such as data, voice and image. The time reference subsystem takes charge
of providing the unified standard time and frequency signals. The auxiliary support
subsystem takes charge of providing the technical supports and logistics services,
such as the meteorological data, geodetic data, power supply and air-conditioning
environment for the control center and TT&C stations; the position, heading and
attitude parameters for the tracking ships; the stable directing beams for the tracking
and measurement antennas; and so on.
Tracking and measuring the orbits and attitudes of spacecrafts have always been
the core tasks of the TT&C system, and thus the tracking and measurement subsystem
is essentially the ground navigation system for spacecrafts, which usually adopts two
kinds of tracking and measuring techniques, optical and radio. For the optical equipment, due to the disadvantages like strict observation condition and limited operating
distance, it is unable to meet the requirements for the spacecraft’s orbit determination
for long-term operation, and thus the optical observations are usually used only in
the stage of launching the spacecrafts into orbits. The radio tracking and measuring
equipment, with the advantages of all-weather, long operating distance, easy information transmission and real-time data processing, usually plays a leading role in
the TT&C system. According to the different working ways, the radio tracking and
measuring equipment can be divided into two types, pulse and continuous wave. The
pulse-type equipment is the measurement radar of transmitting radio-frequency pulse
signals, with the advantages of simple device, as well as single station, single relay
and multi-station working at the same time. The continuous wave-type equipment