5.4 Design Methodology
165
more mass is required and reliability will be lower. There are electric heaters, thermal
switches, variable conductivity heat pipes, single-phase fluid loops, two-phase fluid
loops and loop heat pipes in active thermal control products.
In design of thermal control, at first the passive thermal control measures are
preferred according to changes of external heat flow, internal heat source and temperature requirement of instruments. If the environment is harsh, or the heat source in the
module or instrument changes so greatly that the passive thermal control measures
cannot meet the requirements, the appropriate active thermal control measures can
be selected. The change of the environment faced by the lunar lander was great, and
high temperature in lunar day and low temperature in lunar night was harsh, therefore only passive thermal control measures couldn’t meet the requirements. So, it was
necessary to take more active thermal control measures to control the temperature
range of structure and instruments.
2. Selection of Heat Source and Method of Heat Transfer during Lunar Night
It is up to the lifetime of the lunar lander whether special heat source such as RHU
is necessary. For example, if the lifetime was more than a lunar daytime, the heat
source was necessary to provide heat for survival of the lunar lander in lunar night.
During lunar night, the heat from the heat source should be introduced to the lunar
lander by fluid loops driven by bump, thermal switches, and loop heat pipes. Because
the pump that drove the fluid loop requires electric power, a high-power isotope
thermoelectric generator was necessary to meet the power supply requirement, which
meant a large cost of the system. And there were also active components such as
pump that may affect long-term operation reliability. The solution of thermal switch
with loop heat pipe was feasible, but the thermal switch with moving parts might
cause low reliability and is prone to malfunctions resulting in poor system reliability.
For example, the lifetime of the Chang’E-3 lunar lander on lunar surface was
1 year. It was necessary to use RHU to provide heat. According to configuration of
the lunar lander, two RHUs were used to provide heat for the +Y and −Y modules
of the lunar lander. The isotope material was
238 Pu with 87.7 years half-life period.
Each RHU could provide heat power of 120 W. A two-phase fluid loop driven by
lunar gravity was developed for thermal control subsystem, which could transfer
heat of RHU into instrument modules during lunar night. The two-phase fluid loop
used control valves to realize the on-off control of the fluid loop system as shown in
Fig. 5.7. There was no moving part except control valves, therefore no electric power
or other resource requirement was needed during operation in lunar night, which was
highly reliable.
3. Modular Design
The operation modes of the lunar lander in different phases might be different. The
idea of modular design could isolate thermal coupling among different modules to
reduce thermal impact of the changes in operation modes of instrument. In each
module, the thermal control was independent. Intensive heat exchange was designed
to increase the uniformity of instruments temperature in the module. According to
operation modes of instruments, heat consumption distribution and total amount
165
more mass is required and reliability will be lower. There are electric heaters, thermal
switches, variable conductivity heat pipes, single-phase fluid loops, two-phase fluid
loops and loop heat pipes in active thermal control products.
In design of thermal control, at first the passive thermal control measures are
preferred according to changes of external heat flow, internal heat source and temperature requirement of instruments. If the environment is harsh, or the heat source in the
module or instrument changes so greatly that the passive thermal control measures
cannot meet the requirements, the appropriate active thermal control measures can
be selected. The change of the environment faced by the lunar lander was great, and
high temperature in lunar day and low temperature in lunar night was harsh, therefore only passive thermal control measures couldn’t meet the requirements. So, it was
necessary to take more active thermal control measures to control the temperature
range of structure and instruments.
2. Selection of Heat Source and Method of Heat Transfer during Lunar Night
It is up to the lifetime of the lunar lander whether special heat source such as RHU
is necessary. For example, if the lifetime was more than a lunar daytime, the heat
source was necessary to provide heat for survival of the lunar lander in lunar night.
During lunar night, the heat from the heat source should be introduced to the lunar
lander by fluid loops driven by bump, thermal switches, and loop heat pipes. Because
the pump that drove the fluid loop requires electric power, a high-power isotope
thermoelectric generator was necessary to meet the power supply requirement, which
meant a large cost of the system. And there were also active components such as
pump that may affect long-term operation reliability. The solution of thermal switch
with loop heat pipe was feasible, but the thermal switch with moving parts might
cause low reliability and is prone to malfunctions resulting in poor system reliability.
For example, the lifetime of the Chang’E-3 lunar lander on lunar surface was
1 year. It was necessary to use RHU to provide heat. According to configuration of
the lunar lander, two RHUs were used to provide heat for the +Y and −Y modules
of the lunar lander. The isotope material was
238 Pu with 87.7 years half-life period.
Each RHU could provide heat power of 120 W. A two-phase fluid loop driven by
lunar gravity was developed for thermal control subsystem, which could transfer
heat of RHU into instrument modules during lunar night. The two-phase fluid loop
used control valves to realize the on-off control of the fluid loop system as shown in
Fig. 5.7. There was no moving part except control valves, therefore no electric power
or other resource requirement was needed during operation in lunar night, which was
highly reliable.
3. Modular Design
The operation modes of the lunar lander in different phases might be different. The
idea of modular design could isolate thermal coupling among different modules to
reduce thermal impact of the changes in operation modes of instrument. In each
module, the thermal control was independent. Intensive heat exchange was designed
to increase the uniformity of instruments temperature in the module. According to
operation modes of instruments, heat consumption distribution and total amount