180
5 Thermal Control Technology of Lunar Lander
There were two RHUs installed outside instrument modules in thermal control
subsystem of the Chang’E-3 lunar lander, each of which could produce 120 W heat
power.
5.5.4 Two-Phase Fluid Loop Technology
The RHUs of the Chang’E-3 lunar lander was installed outside instrument modules.
The heat of RHUs should be transferred into instrument modules to maintain instrument temperature. For the Chang’E-3 lunar lander, the heat transfer devices should
not consume any electric power and be highly reliable during continuous operation
of 14 days in lunar night.
The technical challenge of thermal control under low temperature in lunar night
was heat transfer on basis of RHU application. The requirement was to transfer heat
without any electric power consumption. Theoretically the heat of RHU could be
transferred directly into instrument module by heat conduction, or by heat loop pipe,
heat pipe with thermal switch, or by gravity-driven two-phase fluid loop. The thermal
switch was necessary to control heat transfer for design of heat conduction, heat loop
pipe or heat pipe, which should be highly reliable (If the thermal switch failed on
lunar surface, it could result in mission failure).
The gravity-driven two-phase fluid loop is driven autonomously by the density
difference between the vapor in ascending pipeline and the liquid in the return
pipeline under the natural lunar gravity on lunar surface. No electric power or other
resources are necessary during operation and there is no mechanism in the gravitydriven two-phase fluid loop, therefore it is highly reliable, which is suitable for heat
transfer between heat source and instrument modules during lunar night. During
lunar daytime, the loop can be shut off by telecommand to block heat transfer from
heat source to modules. According to its rationale, the gravity driven two-phase fluid
loop cannot work under microgravity conditions in LTO and circumlunar phase, i.e.,
it can only work on ground test and operation on lunar surface.
The gravity-driven two-phase fluid loop technology was applied in thermal control
system of the Chang’E-3 lunar lander, which transferred heat from RHUs into
modules during lunar night. When the two-phase fluid loop was designed, it was
necessary to consider the possible effects of uncertainty of landing attitude on operation of the loop. And the normal operation should be ensured even in the worst case.
The two-phase fluid loop should be designed to be lightweight with no mechanism
and simple structure and highly reliable. There were evaporator, condenser, fluid
tank and pipelines in the two-phase fluid loop with ammonia fluid. There were two
sets of two-phase fluid loops for heat transfer of two RHUs in the Chang’E-3 lunar
lander. The configuration of the two-phase fluid loop of the Chang’E-3 lunar lander
is shown in Fig. 5.17.
When the two-phase fluid loop was working, the loop was in connected state.
Due to a certain height difference between the fluid tank and the evaporator, the fluid
flowed through the evaporator and absorbed heat of the RHU under lunar gravity.
5 Thermal Control Technology of Lunar Lander
There were two RHUs installed outside instrument modules in thermal control
subsystem of the Chang’E-3 lunar lander, each of which could produce 120 W heat
power.
5.5.4 Two-Phase Fluid Loop Technology
The RHUs of the Chang’E-3 lunar lander was installed outside instrument modules.
The heat of RHUs should be transferred into instrument modules to maintain instrument temperature. For the Chang’E-3 lunar lander, the heat transfer devices should
not consume any electric power and be highly reliable during continuous operation
of 14 days in lunar night.
The technical challenge of thermal control under low temperature in lunar night
was heat transfer on basis of RHU application. The requirement was to transfer heat
without any electric power consumption. Theoretically the heat of RHU could be
transferred directly into instrument module by heat conduction, or by heat loop pipe,
heat pipe with thermal switch, or by gravity-driven two-phase fluid loop. The thermal
switch was necessary to control heat transfer for design of heat conduction, heat loop
pipe or heat pipe, which should be highly reliable (If the thermal switch failed on
lunar surface, it could result in mission failure).
The gravity-driven two-phase fluid loop is driven autonomously by the density
difference between the vapor in ascending pipeline and the liquid in the return
pipeline under the natural lunar gravity on lunar surface. No electric power or other
resources are necessary during operation and there is no mechanism in the gravitydriven two-phase fluid loop, therefore it is highly reliable, which is suitable for heat
transfer between heat source and instrument modules during lunar night. During
lunar daytime, the loop can be shut off by telecommand to block heat transfer from
heat source to modules. According to its rationale, the gravity driven two-phase fluid
loop cannot work under microgravity conditions in LTO and circumlunar phase, i.e.,
it can only work on ground test and operation on lunar surface.
The gravity-driven two-phase fluid loop technology was applied in thermal control
system of the Chang’E-3 lunar lander, which transferred heat from RHUs into
modules during lunar night. When the two-phase fluid loop was designed, it was
necessary to consider the possible effects of uncertainty of landing attitude on operation of the loop. And the normal operation should be ensured even in the worst case.
The two-phase fluid loop should be designed to be lightweight with no mechanism
and simple structure and highly reliable. There were evaporator, condenser, fluid
tank and pipelines in the two-phase fluid loop with ammonia fluid. There were two
sets of two-phase fluid loops for heat transfer of two RHUs in the Chang’E-3 lunar
lander. The configuration of the two-phase fluid loop of the Chang’E-3 lunar lander
is shown in Fig. 5.17.
When the two-phase fluid loop was working, the loop was in connected state.
Due to a certain height difference between the fluid tank and the evaporator, the fluid
flowed through the evaporator and absorbed heat of the RHU under lunar gravity.