10.4 Design of Telemetry/Telecommand and Telecommunication Technology
349
Another important function of the phase-locked receiver was to provide the phase
modulation transmitter with a reference frequency signal of the downlink transmitting carrier frequency. There were two operation modes for the phase modulation
transmitter: coherence and incoherence. Under the coherent mode, the reference
frequency signal of the downlink transmitting frequency was output by the voltage
controlled crystal oscillator in the phase-locked loop of the receiver, and the frequency
stability was up to the uplink signal of the telemetry/telecommand ground station.
Under the incoherent mode, the reference frequency signal of the downlink transmitting frequency was output by the temperature compensated crystal oscillator in
the transmitter. The downlink signal of the phase modulation transmitter could be
used as the target acquisition beacon of the ground station, and provide telemetry
downlink, ranging signal forwarding or regeneration.
The ranging sound signal demodulated by the phase-locked receiver and telemetry
sub carrier generated by the OBDH subsystem of the lunar lander were sent to the
ground station after modulated by the phase modulation transmitter. The downlink
telemetry signal was from OBDH subsystem of the lunar lander, which was BPSK
modulated subcarrier signal. The telemetry signal and forward ranging sound signal
were linearly added in the pre-modulator of the transmitter and then modulated
to the downlink carrier. In order to lower the ranging error, it was necessary that
the phase noise should be small enough when the transmitter was forwarding the
range sound. Therefore, the forward signal was not deeply processed, resulting in
the uplink ranging sound signal and remote control command signal transmitted to
the downlink carrier simultaneously. In the process of downlink signal modulation,
the general method was applied that the forward telecommand subcarrier signal was
isolated from the telemetry subcarrier signal and the range signal in the frequency
domain, so as to ensure that the processing of the telemetry subcarrier signal and the
ranging signal by the ground station was not affected.
The function of the power supply module was to convert the primary electric
power supplied by the lunar lander into DC power in all voltages required by the
telemetry/telecommand transponder, and to provide the electric current limit protection according to the requirements of actual operation current and derating design.
At the same time, the input filter must be inserted at the input of the DC converter to
ensure that the output voltage interference pulse was small enough and the isolation
of the input power was improved. The primary power ground of the transponder was
isolated from the second power ground, and there was no direct connection.
3) Power Amplifier
Generally, the Solid State Power Amplifier (SSPA) or Traveling Wave Tube Amplifier
(TWTA) was used to amplify and transmit downlink RF signals in power amplifier of
the lunar lander. The basic functions of the power amplifier were almost the same as
those of the amplifier in other radio systems. However, high reliability, high efficiency
and small size were necessary due to the special mission requirements of the lunar
lander and specific operation environment [5].
In order to be in accordance with the development of new technologies and
new standards in modern telecommunications, electronic countermeasures, radar
349
Another important function of the phase-locked receiver was to provide the phase
modulation transmitter with a reference frequency signal of the downlink transmitting carrier frequency. There were two operation modes for the phase modulation
transmitter: coherence and incoherence. Under the coherent mode, the reference
frequency signal of the downlink transmitting frequency was output by the voltage
controlled crystal oscillator in the phase-locked loop of the receiver, and the frequency
stability was up to the uplink signal of the telemetry/telecommand ground station.
Under the incoherent mode, the reference frequency signal of the downlink transmitting frequency was output by the temperature compensated crystal oscillator in
the transmitter. The downlink signal of the phase modulation transmitter could be
used as the target acquisition beacon of the ground station, and provide telemetry
downlink, ranging signal forwarding or regeneration.
The ranging sound signal demodulated by the phase-locked receiver and telemetry
sub carrier generated by the OBDH subsystem of the lunar lander were sent to the
ground station after modulated by the phase modulation transmitter. The downlink
telemetry signal was from OBDH subsystem of the lunar lander, which was BPSK
modulated subcarrier signal. The telemetry signal and forward ranging sound signal
were linearly added in the pre-modulator of the transmitter and then modulated
to the downlink carrier. In order to lower the ranging error, it was necessary that
the phase noise should be small enough when the transmitter was forwarding the
range sound. Therefore, the forward signal was not deeply processed, resulting in
the uplink ranging sound signal and remote control command signal transmitted to
the downlink carrier simultaneously. In the process of downlink signal modulation,
the general method was applied that the forward telecommand subcarrier signal was
isolated from the telemetry subcarrier signal and the range signal in the frequency
domain, so as to ensure that the processing of the telemetry subcarrier signal and the
ranging signal by the ground station was not affected.
The function of the power supply module was to convert the primary electric
power supplied by the lunar lander into DC power in all voltages required by the
telemetry/telecommand transponder, and to provide the electric current limit protection according to the requirements of actual operation current and derating design.
At the same time, the input filter must be inserted at the input of the DC converter to
ensure that the output voltage interference pulse was small enough and the isolation
of the input power was improved. The primary power ground of the transponder was
isolated from the second power ground, and there was no direct connection.
3) Power Amplifier
Generally, the Solid State Power Amplifier (SSPA) or Traveling Wave Tube Amplifier
(TWTA) was used to amplify and transmit downlink RF signals in power amplifier of
the lunar lander. The basic functions of the power amplifier were almost the same as
those of the amplifier in other radio systems. However, high reliability, high efficiency
and small size were necessary due to the special mission requirements of the lunar
lander and specific operation environment [5].
In order to be in accordance with the development of new technologies and
new standards in modern telecommunications, electronic countermeasures, radar