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10 TT&C and Telecommunication Technology …
The telemetry and telecommand architecture of the Chang’E-1 and the Chang’E2 lunar probes were unified S-band (USB). Compared with the independent carrier
radio telemetry and telecommand equipment (such as radar, telemetry, telecommand
and telecommunication instruments of continuous wave), USB could implement
multi telemetry and telecommand tasks simultaneously with only one carrier. Therefore it could alleviate the radio frequency congestion and was of great importance to
increasingly strained frequency band resources, while the onboard radio frequency
instruments could be simplified so as to reduce volume, mass and power consumption
of onboard instruments. It was more suitable for requirements of function integration
and miniaturization for deep space missions.
The USB architecture was the main telemetry and telecommand architecture of
the Chang’E-1 and the Chang’E-2 lunar probes. On the Chang’E-2 lunar probe,
a unified X-band (UXB) telemetry and telecommand instrument was onboard to
demonstrate UXB architecture on orbit. The transition from USB to UXB of deep
space mission in China was achieved by the Chang’E-3 lunar lander, on which UXB
was the main telemetry and telecommand architecture. As one of the development
trends of deep space missions, UXB architecture had some advantages: (1) The
frequency band resources of X-band were more abundant than those of the S-band,
which could ensure the signal isolation among space mission in term of frequency
division and improve the capacity of the channel to make it easier to design; (2) When
the frequency was higher, the accuracy of velocity measurement for the lunar lander
could be higher; and (3) The radio instruments of X-band was generally smaller
than those of S-band, which was more conducive to lightweight and miniaturization
design of passive radio frequency instruments.
The onboard telecommunication system was used to complete downlink of the
massive exploration data which is generally scientific exploration data of the lunar
lander. It was not necessary to realize multifunction reuse relative to the telemetry
and telecommand architecture (such as telemetry, ranging and angular measurement
signals modulated in the telemetry and telecommand downlink channel simultaneously). Furthermore, the telecommunication data of lunar missions was relatively
lower than that of remote sensing spacecraft on near Earth orbit, and the frequency
band resource was not the main contradiction, so the suppressed carrier modulation
architecture was commonly used around world. The BPSK modulation architecture
of the Chang’E-3 was the same as the Chang’E-1 and the Chang’E-2, except that
the radio frequency was changed from S-band to X-band just like the telemetry and
telecommand architecture.
In order to minimize of interference of Earth atmosphere on radio signals (it
could be approximately regarded as a vacuum environment on lunar surface) and
other factors such as the possible polarization mismatch, the telemetry/telecommand
and telecommunication antenna was generally circular polarized and different polarization directions (left or right) for receiving and transmitting antennas should be
designed to increase isolation of reception and transmission. At the same time, in
order to ensure the real-time telemetry and telecommand of the lunar lander and
improve the reliability of the mission, the telemetry and telecommand antenna should
guarantee the coverage of the full space, so that the telemetry and telecommand of
10 TT&C and Telecommunication Technology …
The telemetry and telecommand architecture of the Chang’E-1 and the Chang’E2 lunar probes were unified S-band (USB). Compared with the independent carrier
radio telemetry and telecommand equipment (such as radar, telemetry, telecommand
and telecommunication instruments of continuous wave), USB could implement
multi telemetry and telecommand tasks simultaneously with only one carrier. Therefore it could alleviate the radio frequency congestion and was of great importance to
increasingly strained frequency band resources, while the onboard radio frequency
instruments could be simplified so as to reduce volume, mass and power consumption
of onboard instruments. It was more suitable for requirements of function integration
and miniaturization for deep space missions.
The USB architecture was the main telemetry and telecommand architecture of
the Chang’E-1 and the Chang’E-2 lunar probes. On the Chang’E-2 lunar probe,
a unified X-band (UXB) telemetry and telecommand instrument was onboard to
demonstrate UXB architecture on orbit. The transition from USB to UXB of deep
space mission in China was achieved by the Chang’E-3 lunar lander, on which UXB
was the main telemetry and telecommand architecture. As one of the development
trends of deep space missions, UXB architecture had some advantages: (1) The
frequency band resources of X-band were more abundant than those of the S-band,
which could ensure the signal isolation among space mission in term of frequency
division and improve the capacity of the channel to make it easier to design; (2) When
the frequency was higher, the accuracy of velocity measurement for the lunar lander
could be higher; and (3) The radio instruments of X-band was generally smaller
than those of S-band, which was more conducive to lightweight and miniaturization
design of passive radio frequency instruments.
The onboard telecommunication system was used to complete downlink of the
massive exploration data which is generally scientific exploration data of the lunar
lander. It was not necessary to realize multifunction reuse relative to the telemetry
and telecommand architecture (such as telemetry, ranging and angular measurement
signals modulated in the telemetry and telecommand downlink channel simultaneously). Furthermore, the telecommunication data of lunar missions was relatively
lower than that of remote sensing spacecraft on near Earth orbit, and the frequency
band resource was not the main contradiction, so the suppressed carrier modulation
architecture was commonly used around world. The BPSK modulation architecture
of the Chang’E-3 was the same as the Chang’E-1 and the Chang’E-2, except that
the radio frequency was changed from S-band to X-band just like the telemetry and
telecommand architecture.
In order to minimize of interference of Earth atmosphere on radio signals (it
could be approximately regarded as a vacuum environment on lunar surface) and
other factors such as the possible polarization mismatch, the telemetry/telecommand
and telecommunication antenna was generally circular polarized and different polarization directions (left or right) for receiving and transmitting antennas should be
designed to increase isolation of reception and transmission. At the same time, in
order to ensure the real-time telemetry and telecommand of the lunar lander and
improve the reliability of the mission, the telemetry and telecommand antenna should
guarantee the coverage of the full space, so that the telemetry and telecommand of