10.4 Design of Telemetry/Telecommand and Telecommunication Technology
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and the lunar rover. According to the requirements, there was a UHF telecommunication channel on lunar surface between the lunar lander and the lunar rover. The
lunar lander could receive the exploration and telemetry data from the lunar rover
and send it back to the ground station through its own telecommunication channel.
The orbit determination of the lunar lander consisted of velocity measurement, ranging measurement and angle measurement. Because of the long distance
between the lander lunar and the ground, the interferometric measurement technology was widely used in global deep space missions to ensure the accuracy of
orbit determination [8].
The Very Long Baseline Interferometry (VLBI) developed in 1960s has a great
advantage in deep space exploration at long distance. The VLBI system consisted
of two or more radio telescopes at several thousand to tens of thousands kilometers
away to realize the precise measurement of the extragalactic radio celestial bodies,
the deep space and the artificial celestial bodies at high altitude. Because of the high
measurement accuracy, it has been widely applied in deep space exploration [12].
VLBI was the most accurate deep space angle measurement technology. In order
to eliminate or weaken the clock deviation between stations, the station site deviation
and the deviation caused by signal propagation path in the measurement process, the
DOR technology was generally applied. An extragalactic radio source with a small
angular distance from the lunar lander (the separation angle is generally less than
10°) as the second observation was introduced in the DOR technology. By the
difference of two kinds of observations, the errors such as the station site deviation,
atmospheric deviation, delay deviation of receiving equipment and clock deviation
could be basically eliminated and the accuracy of time delay measurement could
be improved. The principle of DOR technology is that the DOR beacon from the
spacecraft is tracked by two remote ground stations at the same time and the angle
relation between the spacecraft and the ground station was calculated according to
the difference value of time used for beacons to reach two ground stations (delay
time).
When two spacecraft (such as the lunar lander and the lunar rover) were very
close in the angle, they could be observed in the same beam of the observation station
antenna. Observing two spacecraft by two stations at the same time could generate
differential interferometry observation, which was called the same beam interferometry measurement. From observation on Earth, the angle between two spacecrafts was
much smaller than that between the spacecraft and the radio star (10°). Because many
measurement deviations were proportional to the angle, the measurement between
the spacecraft could be more accurate than the DOR interferometry. If two spacecrafts were located in the same antenna beam, the carrier phase of two spacecraft
could be tracked simultaneously. By using carrier phase instead of group delay (or
delay rate), the accuracy of measurement could be further improved. The Same
Beam Interferometry (SBI) had some operational advantages over traditional spacecraft interferometry: it was not necessary to calibrate the system with radio source,
and there was no related step in data processing, so that real-time phase measurement of spacecraft could be realized. The processing of phase measurement data
was more like traditional Doppler data. The same beam interference data combined
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and the lunar rover. According to the requirements, there was a UHF telecommunication channel on lunar surface between the lunar lander and the lunar rover. The
lunar lander could receive the exploration and telemetry data from the lunar rover
and send it back to the ground station through its own telecommunication channel.
The orbit determination of the lunar lander consisted of velocity measurement, ranging measurement and angle measurement. Because of the long distance
between the lander lunar and the ground, the interferometric measurement technology was widely used in global deep space missions to ensure the accuracy of
orbit determination [8].
The Very Long Baseline Interferometry (VLBI) developed in 1960s has a great
advantage in deep space exploration at long distance. The VLBI system consisted
of two or more radio telescopes at several thousand to tens of thousands kilometers
away to realize the precise measurement of the extragalactic radio celestial bodies,
the deep space and the artificial celestial bodies at high altitude. Because of the high
measurement accuracy, it has been widely applied in deep space exploration [12].
VLBI was the most accurate deep space angle measurement technology. In order
to eliminate or weaken the clock deviation between stations, the station site deviation
and the deviation caused by signal propagation path in the measurement process, the
DOR technology was generally applied. An extragalactic radio source with a small
angular distance from the lunar lander (the separation angle is generally less than
10°) as the second observation was introduced in the DOR technology. By the
difference of two kinds of observations, the errors such as the station site deviation,
atmospheric deviation, delay deviation of receiving equipment and clock deviation
could be basically eliminated and the accuracy of time delay measurement could
be improved. The principle of DOR technology is that the DOR beacon from the
spacecraft is tracked by two remote ground stations at the same time and the angle
relation between the spacecraft and the ground station was calculated according to
the difference value of time used for beacons to reach two ground stations (delay
time).
When two spacecraft (such as the lunar lander and the lunar rover) were very
close in the angle, they could be observed in the same beam of the observation station
antenna. Observing two spacecraft by two stations at the same time could generate
differential interferometry observation, which was called the same beam interferometry measurement. From observation on Earth, the angle between two spacecrafts was
much smaller than that between the spacecraft and the radio star (10°). Because many
measurement deviations were proportional to the angle, the measurement between
the spacecraft could be more accurate than the DOR interferometry. If two spacecrafts were located in the same antenna beam, the carrier phase of two spacecraft
could be tracked simultaneously. By using carrier phase instead of group delay (or
delay rate), the accuracy of measurement could be further improved. The Same
Beam Interferometry (SBI) had some operational advantages over traditional spacecraft interferometry: it was not necessary to calibrate the system with radio source,
and there was no related step in data processing, so that real-time phase measurement of spacecraft could be realized. The processing of phase measurement data
was more like traditional Doppler data. The same beam interference data combined