250
4 Navigations from Ground to Space
adopts the ways of continuously transmitting radio-frequency signals, which is easy
to realize the comprehensive utilization of velocity measurements and carrier signals,
mainly including Doppler velocity measurement unit, range and its rate measurement unit and microwave-unified unit. The microwave-unified units share the same
microwave carrier channel and a set of antennas, functionally integrating the tracking
and measurement together with the telemetry, remote control and communication,
and thus it is widely used in the TT&C and communication for spacecrafts.
4.8.1.2 Framework of TT&C System
The tracks of projecting the spacecraft’s flight orbits on the Earth’s surface, usually
known as sub-satellite point tracks, are mostly with the shapes round the globe,
and only the sub-satellite point tracks of the geosynchronous orbit satellites are
“8” shape. Usually, the TT&C equipment is deployed along the sub-satellite point
tracks on the surface of the Earth. In order to achieve the tracking measurement and
communication coverage with a large arc-segment for a spacecraft, it is necessary
to consider the deployment of the TT&C stations within the global range and even
build the space-based relay stations. From the perspective of system architecture,
the TT&C system is composed of many TT&C units. The so-called TT&C unit
refers to an organic combination of several functional TT&C subsystems, and as a
relatively independent unit, it is usually placed in the appropriate site near the subsatellite points to perform the space TT&C tasks with special functions. In general,
there are two basic types of the TT&C units, control center and TT&C stations. In
other words, the TT&C system is composed of one control center and a number of
widely distributed TT&C stations. Each scattered node unit can be connected into an
organic whole through the time-unified and communication, forming an information
exchange network under the same time reference, which is called TT&C network,
as shown in Fig. 4.10.
The control center is the central measurement and control unit for the TT&C
network, consisting of the data processing, monitoring display, command communication, voice communication, data transmission, television monitoring and other
equipment. According to the different division of tasks, the control center is also
divided into the operation center of TT&C network, and the mission command and
control center, where the former takes charges of the organization, coordination,
operation and management of the TT&C network, and the latter takes charges of
planning and organizing the spaceflight missions, as well as monitoring and operating
the spacecraft’s flight states. Currently, the TT&C network has achieved automatic
operation control. The control center, TT&C stations and their devices are equipped
with remote monitoring and controlling system. According to the requirements for
the practical flight missions, the control center can dispatch and allocate the TT&C
stations and their devices through the remote commands, and set the working parameters for the equipment. Meanwhile, the state parameters of TT&C devices can also
be collected by the remote monitoring system of the TT&C stations, and sent to the
4 Navigations from Ground to Space
adopts the ways of continuously transmitting radio-frequency signals, which is easy
to realize the comprehensive utilization of velocity measurements and carrier signals,
mainly including Doppler velocity measurement unit, range and its rate measurement unit and microwave-unified unit. The microwave-unified units share the same
microwave carrier channel and a set of antennas, functionally integrating the tracking
and measurement together with the telemetry, remote control and communication,
and thus it is widely used in the TT&C and communication for spacecrafts.
4.8.1.2 Framework of TT&C System
The tracks of projecting the spacecraft’s flight orbits on the Earth’s surface, usually
known as sub-satellite point tracks, are mostly with the shapes round the globe,
and only the sub-satellite point tracks of the geosynchronous orbit satellites are
“8” shape. Usually, the TT&C equipment is deployed along the sub-satellite point
tracks on the surface of the Earth. In order to achieve the tracking measurement and
communication coverage with a large arc-segment for a spacecraft, it is necessary
to consider the deployment of the TT&C stations within the global range and even
build the space-based relay stations. From the perspective of system architecture,
the TT&C system is composed of many TT&C units. The so-called TT&C unit
refers to an organic combination of several functional TT&C subsystems, and as a
relatively independent unit, it is usually placed in the appropriate site near the subsatellite points to perform the space TT&C tasks with special functions. In general,
there are two basic types of the TT&C units, control center and TT&C stations. In
other words, the TT&C system is composed of one control center and a number of
widely distributed TT&C stations. Each scattered node unit can be connected into an
organic whole through the time-unified and communication, forming an information
exchange network under the same time reference, which is called TT&C network,
as shown in Fig. 4.10.
The control center is the central measurement and control unit for the TT&C
network, consisting of the data processing, monitoring display, command communication, voice communication, data transmission, television monitoring and other
equipment. According to the different division of tasks, the control center is also
divided into the operation center of TT&C network, and the mission command and
control center, where the former takes charges of the organization, coordination,
operation and management of the TT&C network, and the latter takes charges of
planning and organizing the spaceflight missions, as well as monitoring and operating
the spacecraft’s flight states. Currently, the TT&C network has achieved automatic
operation control. The control center, TT&C stations and their devices are equipped
with remote monitoring and controlling system. According to the requirements for
the practical flight missions, the control center can dispatch and allocate the TT&C
stations and their devices through the remote commands, and set the working parameters for the equipment. Meanwhile, the state parameters of TT&C devices can also
be collected by the remote monitoring system of the TT&C stations, and sent to the