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10 TT&C and Telecommunication Technology …
lunar atmosphere (almost vacuum) and lunar reflector. Due to existence of lunar
reflector, the field distribution is complex and variable. The channel model cannot
be simply equivalent to the probe-ground link model.
3. Complex Operation Modes
Compared with Earth orbit spacecraft, there were flight phases including LTO,
circumlunar orbit, powered descent and operation on lunar surface for the lunar
lander. The antenna of the lunar lander should be able to ensure full space coverage,
so as to achieve telemetry and telecommand in all mission phases for reliable mission
success. At the same time, because of relatively complex surface status of the lunar
lander, there might be negative affection to antenna pattern which imposes stringent
constraint for layout of antenna.
Powered descent was one of the key steps in soft-landing mission. It was generally
required to ensure that the information such as image during landing process can be
transmitted to ground station in real time. In order to achieve the high data rate
transmission during powered descent, corresponding telecommunication channel
should be configured. Generally, the telecommunication channel shall be provided
by high gain antenna with mechanism to implement telecommunication to ground.
However, the landing impact was severe during soft-landing and it was not suitable
for mechanism. For example, the telecommunication antenna was fixed on outer
surface of the Chang’E-3 lunar lander. At the same time, because of attitude control
error of the lunar lander, a wide beam antenna was applied to implement downlink
transmission of image data in powered descent.
10.3.3 Design Constraints
1. Long Distance
The telecommunication distance of the lunar lander was further than that of Earth
spacecraft to ground station and there might be more link loss about 20 dB. In order
to overcome the large path loss in long distance, deep space network could be built up
on ground, and high sensitivity receiver and high power amplifier should be onboard
the lunar lander. In the second phase of China Lunar Exploration Program, a global
deep space network was initiated to be built up, including 35 m deep space station
in Kashi, 66 m deep space station in Jiamusi and 35 m deep space station in the
west Argentina, which could realize the 90% coverage of telemetry/telecommand
and telecommunication for the lunar lander [5].
2. Frequency
According to the recommendation of CCSDS, the S/X/Ka frequency band could
be applied for the lunar lander-ground telemetry/telecommand and telecommunication. The Ka band telecommunication was limited by the engineering difficulty
of large aperture antenna on ground, which was usually used only as a test link,
10 TT&C and Telecommunication Technology …
lunar atmosphere (almost vacuum) and lunar reflector. Due to existence of lunar
reflector, the field distribution is complex and variable. The channel model cannot
be simply equivalent to the probe-ground link model.
3. Complex Operation Modes
Compared with Earth orbit spacecraft, there were flight phases including LTO,
circumlunar orbit, powered descent and operation on lunar surface for the lunar
lander. The antenna of the lunar lander should be able to ensure full space coverage,
so as to achieve telemetry and telecommand in all mission phases for reliable mission
success. At the same time, because of relatively complex surface status of the lunar
lander, there might be negative affection to antenna pattern which imposes stringent
constraint for layout of antenna.
Powered descent was one of the key steps in soft-landing mission. It was generally
required to ensure that the information such as image during landing process can be
transmitted to ground station in real time. In order to achieve the high data rate
transmission during powered descent, corresponding telecommunication channel
should be configured. Generally, the telecommunication channel shall be provided
by high gain antenna with mechanism to implement telecommunication to ground.
However, the landing impact was severe during soft-landing and it was not suitable
for mechanism. For example, the telecommunication antenna was fixed on outer
surface of the Chang’E-3 lunar lander. At the same time, because of attitude control
error of the lunar lander, a wide beam antenna was applied to implement downlink
transmission of image data in powered descent.
10.3.3 Design Constraints
1. Long Distance
The telecommunication distance of the lunar lander was further than that of Earth
spacecraft to ground station and there might be more link loss about 20 dB. In order
to overcome the large path loss in long distance, deep space network could be built up
on ground, and high sensitivity receiver and high power amplifier should be onboard
the lunar lander. In the second phase of China Lunar Exploration Program, a global
deep space network was initiated to be built up, including 35 m deep space station
in Kashi, 66 m deep space station in Jiamusi and 35 m deep space station in the
west Argentina, which could realize the 90% coverage of telemetry/telecommand
and telecommunication for the lunar lander [5].
2. Frequency
According to the recommendation of CCSDS, the S/X/Ka frequency band could
be applied for the lunar lander-ground telemetry/telecommand and telecommunication. The Ka band telecommunication was limited by the engineering difficulty
of large aperture antenna on ground, which was usually used only as a test link,