4.8 Ground Navigation Networks for Spacecrafts
259
GLONASS satellite via the upload stations. The central synchronizer implements the
GLONASS system timescale by the means of a high-precise hydrogen atomic clock.
The Russian State Etalon UTC allows the synchronization of the cesium atomic
clocks onboard the GLONASS satellites.
The TT&C stations track the GLONASS satellites in view, and collect ranging data
and telemetry from the satellites. All of the ranging data and telemetry are transmitted
to the SCC for processing and analyzing. Moreover, both the monitor stations and the
laser ranging stations track and measure the satellites, whose measurement data is
used to precisely determine the orbit and clock parameters of each GLONASS satellite at the SCC. As a single source of calibration data for the GLONASS ephemeris
determination, the advantages of the laser ranging stations are: to provide the means
of accuracy estimating and radio-frequency calibrating for the GLONASS satellite’s
orbit measurements; to monitor the onboard clocks and allow use of the data for operational control of the GLONASS time and ephemeris data, with geodetic-class RF
navigation receivers connected to hydrogen maser frequency standards; to use their
site coordinates as a geodetic base for the GLONASS reference frame; to present the
declared value of ephemeris precision for the satellites using the laser ranging data.
4.8.3 Ground Deep Space Networks
According to the definition of “Deep Space” by the ITU, the space range of more than
2 × 10
6 km away from the Earth’s surface is called deep space. In the terms of this
definition, the deep-space exploration frequency band specified by the ITU would
not be used in the exploring activities for the Moon and even the Lagrange Points
L1 and L2 in the Sun–Earth space. From the current situation of space activities, the
spacecrafts that explore the Moon, planets and interplanetary space are called deepspace probes, and the ground networks that track, navigate and communicate for the
deep-space probes are called ground deep-space networks or ground navigation
networks for the deep-space probes. The networks have the functions of tracking
and measuring the probe’s orbits, receiving and processing the telemetry information
and scientific data from the probes, and monitoring and controlling the operational
states of the probes. Generally, according to the difference of basic working units,
the deep-space TT&C network can be divided into deep-space stations, communication links and computing control center in its architecture. According to the
different uses of the TT&C units, the network is composed of many subsystems,
such as tracking, downlink telemetry and demodulation, digital detection information
demodulation, uplink command modulation, uplink data modulation, communication, data processing, operational control and simulation. According to the different
using ranges and exploring objects, the networks are divided into the TT&C networks
for lunar exploration and for planets and interstellar space explorations, and between
the two networks, there are discrepancies in acting range, principle of measuring
angle and operational control. Compared with the TT&C for the spacecrafts in the
near-Earth orbits, the difficulty of deep-space exploration is to solve the TT&C
259
GLONASS satellite via the upload stations. The central synchronizer implements the
GLONASS system timescale by the means of a high-precise hydrogen atomic clock.
The Russian State Etalon UTC allows the synchronization of the cesium atomic
clocks onboard the GLONASS satellites.
The TT&C stations track the GLONASS satellites in view, and collect ranging data
and telemetry from the satellites. All of the ranging data and telemetry are transmitted
to the SCC for processing and analyzing. Moreover, both the monitor stations and the
laser ranging stations track and measure the satellites, whose measurement data is
used to precisely determine the orbit and clock parameters of each GLONASS satellite at the SCC. As a single source of calibration data for the GLONASS ephemeris
determination, the advantages of the laser ranging stations are: to provide the means
of accuracy estimating and radio-frequency calibrating for the GLONASS satellite’s
orbit measurements; to monitor the onboard clocks and allow use of the data for operational control of the GLONASS time and ephemeris data, with geodetic-class RF
navigation receivers connected to hydrogen maser frequency standards; to use their
site coordinates as a geodetic base for the GLONASS reference frame; to present the
declared value of ephemeris precision for the satellites using the laser ranging data.
4.8.3 Ground Deep Space Networks
According to the definition of “Deep Space” by the ITU, the space range of more than
2 × 10
6 km away from the Earth’s surface is called deep space. In the terms of this
definition, the deep-space exploration frequency band specified by the ITU would
not be used in the exploring activities for the Moon and even the Lagrange Points
L1 and L2 in the Sun–Earth space. From the current situation of space activities, the
spacecrafts that explore the Moon, planets and interplanetary space are called deepspace probes, and the ground networks that track, navigate and communicate for the
deep-space probes are called ground deep-space networks or ground navigation
networks for the deep-space probes. The networks have the functions of tracking
and measuring the probe’s orbits, receiving and processing the telemetry information
and scientific data from the probes, and monitoring and controlling the operational
states of the probes. Generally, according to the difference of basic working units,
the deep-space TT&C network can be divided into deep-space stations, communication links and computing control center in its architecture. According to the
different uses of the TT&C units, the network is composed of many subsystems,
such as tracking, downlink telemetry and demodulation, digital detection information
demodulation, uplink command modulation, uplink data modulation, communication, data processing, operational control and simulation. According to the different
using ranges and exploring objects, the networks are divided into the TT&C networks
for lunar exploration and for planets and interstellar space explorations, and between
the two networks, there are discrepancies in acting range, principle of measuring
angle and operational control. Compared with the TT&C for the spacecrafts in the
near-Earth orbits, the difficulty of deep-space exploration is to solve the TT&C