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5 Thermal Control Technology of Lunar Lander
2. Design Constraints
There were design constraints for thermal control subsystem of the lunar lander
including environmental conditions during launch, nominal lifetime, thermal
boundary of engine, and the uncertainty of the landing attitude and operation modes
of instruments.
1) Environmental conditions during launch
Thermal control subsystem shall adapt to the mechanical conditions and thermal
environmental conditions during launch. Based on experience of other spacecraft,
general thermal control products can withstand mechanical conditions during launch,
but effects of acceleration on the working conditions and performance of heat pipes,
fluid loops and other products shall be considered.
As there was heat insulation in launch vehicle fairing, although the temperature
of the outside surface of the fairing was high due to the aerodynamic heating, it had
less effect on instruments of the lunar lander. Due to the short duration of launch
phase, the temperature of instruments on outer surface of the lunar lander would
not exceed allowed temperature level. After jettison of fairing, the temperature of
internal instruments would generally not exceed allowed value because of thermal
inertia of the lunar lander and onboard instruments.
2) Lifetime
If the lifetime of the lunar lander on lunar surface was less than one lunar daytime
after landing, there was no need to consider the issue of survival in lunar night. Then
the thermal design was relatively simple, while single-phase fluid loop and heat pipe
could be used for heat transfer, or an evaporator (or sublimation) consumption heat
sinks for heat dissipation. Through setting a reasonable landing time, landing points
for such the lunar lander could even be selected near lunar equator.
If the lifetime of the lunar lander was longer than one lunar daytime after landing
(for example, the lunar lander with lifetime of one year will experience about 13
cycles of lunar day and night), it was necessary to consider the issue of survival in
lunar night as well as the long-term high temperature in lunar daytime. In order to
provide heat required for survival during lunar night, isotope materials were usually
used instead of large-capacity battery because of large mass requirement. The isotope
materials could provide heat for the lunar lander by utilizing the heat generated
by radioactive decay. Because of uncertainties such as impact of lunar dust, high
temperature issue in lunar daytime must also be paid attention to in thermal design.
There would be requirement of heat dissipation for thermal control subsystem if the
landing point is chosen to be near lunar equator.
3) High temperature boundary of engine
A large engine was used by the lunar lander to perform lunar orbit insertion and softlanding on lunar surface, while small thrusters (such as 150 N and 10 N thrusters) were
used to realize attitude control and assist landing. Due to the long-term working and
high temperatures (throat temperature exceeding 1300 °C, as shown in Fig. 5.6), the
5 Thermal Control Technology of Lunar Lander
2. Design Constraints
There were design constraints for thermal control subsystem of the lunar lander
including environmental conditions during launch, nominal lifetime, thermal
boundary of engine, and the uncertainty of the landing attitude and operation modes
of instruments.
1) Environmental conditions during launch
Thermal control subsystem shall adapt to the mechanical conditions and thermal
environmental conditions during launch. Based on experience of other spacecraft,
general thermal control products can withstand mechanical conditions during launch,
but effects of acceleration on the working conditions and performance of heat pipes,
fluid loops and other products shall be considered.
As there was heat insulation in launch vehicle fairing, although the temperature
of the outside surface of the fairing was high due to the aerodynamic heating, it had
less effect on instruments of the lunar lander. Due to the short duration of launch
phase, the temperature of instruments on outer surface of the lunar lander would
not exceed allowed temperature level. After jettison of fairing, the temperature of
internal instruments would generally not exceed allowed value because of thermal
inertia of the lunar lander and onboard instruments.
2) Lifetime
If the lifetime of the lunar lander on lunar surface was less than one lunar daytime
after landing, there was no need to consider the issue of survival in lunar night. Then
the thermal design was relatively simple, while single-phase fluid loop and heat pipe
could be used for heat transfer, or an evaporator (or sublimation) consumption heat
sinks for heat dissipation. Through setting a reasonable landing time, landing points
for such the lunar lander could even be selected near lunar equator.
If the lifetime of the lunar lander was longer than one lunar daytime after landing
(for example, the lunar lander with lifetime of one year will experience about 13
cycles of lunar day and night), it was necessary to consider the issue of survival in
lunar night as well as the long-term high temperature in lunar daytime. In order to
provide heat required for survival during lunar night, isotope materials were usually
used instead of large-capacity battery because of large mass requirement. The isotope
materials could provide heat for the lunar lander by utilizing the heat generated
by radioactive decay. Because of uncertainties such as impact of lunar dust, high
temperature issue in lunar daytime must also be paid attention to in thermal design.
There would be requirement of heat dissipation for thermal control subsystem if the
landing point is chosen to be near lunar equator.
3) High temperature boundary of engine
A large engine was used by the lunar lander to perform lunar orbit insertion and softlanding on lunar surface, while small thrusters (such as 150 N and 10 N thrusters) were
used to realize attitude control and assist landing. Due to the long-term working and
high temperatures (throat temperature exceeding 1300 °C, as shown in Fig. 5.6), the