5.6 Testing and Verification
183
the pressure shall not be higher than 1 × 10
−3 Pa in the space environment simulator
during thermal balance test.
Space background heat sink (black body radiation of about 4 K) can be simulated
by liquid nitrogen heat sink in a space environment simulator. The surface of heat
sink is usually black painted with infrared emissivity with ε H greater than 0.9. The
heat sink temperature shall not be higher than 100 K during thermal balance test.
For a 100 K heat sink, the radiation energy intensity during the test is approximately
5 W/m
2 , equivalent to 2.3% of the Earth’s infrared radiation heat flux (220 W/m
2 ). The
error will not significantly affect test result. Liquid nitrogen heat sink is acceptable in
engineering implementation as other spacecraft. Compared with liquid helium and
other heat sink, the liquid nitrogen heat sink can simplify the simulation and reduce
the cost greatly.
After the lunar lander was landed on lunar surface, the temperature of components
such as landing legs would be affected by thermal conductivity of lunar surface
and the temperature of the lunar lander would be affected by lunar surface infrared
radiation and reflected of solar heat flow. In the thermal balance test, the radiation of
lunar surface and the reflected heat flow were generally equivalent to external heat
flow, and the thermal effect of lunar surface heat conduction was simulated by the
surface temperature contacted with lunar surface. Thus, it was possible to simulate
lunar surface environment with same method as for space thermal environment in
orbit.
3. Simulation of External Heat Flow
The external heat flow of the lunar lander included solar radiation, lunar infrared
radiation and lunar albedo. The simulation accuracy of external heat flow directly
affected thermal balance temperature level of the lunar lander. The simulation method
of external heat flow should be determined in design of thermal balance test.
The simulation methods of external heat flow included non-contact type and
contact type up to date. There were solar simulator, infrared heater (such as infrared
array, far-infrared cage, heating plate and etc.) in non-contact simulation methods
of external heat flow to simulate incident heat flow onto surface of the lunar lander.
The spectrum and irradiance of the solar simulator should be measured in advance
to meet the requirements when it was used to simulate solar radiation heat flow
directly. Generally, a heat flow measurement device with same state as surface of
the lunar lander was necessary when other non-contact methods are used to simulate
the total incident external heat flow. Except solar simulator, the response time of
other non-contact simulation systems of external heat flow were generally longer
and suitable for steady state test conditions. When the solar simulator was used,
a motion simulator was necessary to simulate the change of relative position and
attitude between solar radiation and the lunar lander in orbit, which might make
the test system relatively complicated. In contact-type simulation of external heat
flow, flexible film-type electric heater was installed on surface of the lunar lander to
simulate heat absorption flow on surface of the lunar lander. Due to fast response
of the electric heating method, the contact-type simulation method of external heat
flow was suitable for transient and quasi-transient test conditions.
183
the pressure shall not be higher than 1 × 10
−3 Pa in the space environment simulator
during thermal balance test.
Space background heat sink (black body radiation of about 4 K) can be simulated
by liquid nitrogen heat sink in a space environment simulator. The surface of heat
sink is usually black painted with infrared emissivity with ε H greater than 0.9. The
heat sink temperature shall not be higher than 100 K during thermal balance test.
For a 100 K heat sink, the radiation energy intensity during the test is approximately
5 W/m
2 , equivalent to 2.3% of the Earth’s infrared radiation heat flux (220 W/m
2 ). The
error will not significantly affect test result. Liquid nitrogen heat sink is acceptable in
engineering implementation as other spacecraft. Compared with liquid helium and
other heat sink, the liquid nitrogen heat sink can simplify the simulation and reduce
the cost greatly.
After the lunar lander was landed on lunar surface, the temperature of components
such as landing legs would be affected by thermal conductivity of lunar surface
and the temperature of the lunar lander would be affected by lunar surface infrared
radiation and reflected of solar heat flow. In the thermal balance test, the radiation of
lunar surface and the reflected heat flow were generally equivalent to external heat
flow, and the thermal effect of lunar surface heat conduction was simulated by the
surface temperature contacted with lunar surface. Thus, it was possible to simulate
lunar surface environment with same method as for space thermal environment in
orbit.
3. Simulation of External Heat Flow
The external heat flow of the lunar lander included solar radiation, lunar infrared
radiation and lunar albedo. The simulation accuracy of external heat flow directly
affected thermal balance temperature level of the lunar lander. The simulation method
of external heat flow should be determined in design of thermal balance test.
The simulation methods of external heat flow included non-contact type and
contact type up to date. There were solar simulator, infrared heater (such as infrared
array, far-infrared cage, heating plate and etc.) in non-contact simulation methods
of external heat flow to simulate incident heat flow onto surface of the lunar lander.
The spectrum and irradiance of the solar simulator should be measured in advance
to meet the requirements when it was used to simulate solar radiation heat flow
directly. Generally, a heat flow measurement device with same state as surface of
the lunar lander was necessary when other non-contact methods are used to simulate
the total incident external heat flow. Except solar simulator, the response time of
other non-contact simulation systems of external heat flow were generally longer
and suitable for steady state test conditions. When the solar simulator was used,
a motion simulator was necessary to simulate the change of relative position and
attitude between solar radiation and the lunar lander in orbit, which might make
the test system relatively complicated. In contact-type simulation of external heat
flow, flexible film-type electric heater was installed on surface of the lunar lander to
simulate heat absorption flow on surface of the lunar lander. Due to fast response
of the electric heating method, the contact-type simulation method of external heat
flow was suitable for transient and quasi-transient test conditions.