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8 Propulsion Technology of Lunar Lander
was relatively much lower and not necessary to be considered. For large-scale, heavy
and high load components such as propellant tank, gas tank, orbit control engine and
etc., the pressure bearing should be satisfied, as well as mechanical environment in
launch phase, stiffness and strength of the lunar lander, otherwise there might be
structural deformation, instability and even broken due to insufficient stiffness or
strength.
For gas or liquid propellant in propulsion subsystem, there were requirements for
temperature condition of individual components in order to prevent liquid propellant
freezing in low temperature, vaporization in high temperature, pressure dramatic
rise, propellant decomposition and even explosion, especially for components
outside the lunar lander like engines, pipelines, valves, and even tanks, gas tanks
which were directly exposed (outside environment: high temperature can be more
than 150 °C in sun light, low temperature can be lower than −100 °C in the shadow).
In order to ensure reliable work of subsystem components, it was necessary to
control the temperature of individual components by thermal design. Generally, the
temperature range of components for liquid such as pipelines, tanks, valves, engines
should be 0~40 °C, while the temperature range of components for gas shall be −
30~70 °C. For the engines/nozzles exposed outside the lunar lander experiencing the
high/low temperature alternation which was much less than the temperature range
of radiation-cooling nozzle, it had almost no impact on nozzle materials (nozzle
is made of niobium-hafnium, niobium-tungsten, rhenium-iridium, carbon/carbon,
carbon/carborundum with high temperature anti oxidizing coatings). It should be
especially emphasized that external high/low temperature can transfer heat to engine
head through nozzle, which might lead to temperature rise or decline in engine head
and valves. In severe low temperature propellant in valves could be frozen with deflagration in cold starting. The high temperature might lead to propellant vaporization
which had impact on normal opening of valves and engine firing. So it was necessary
to conduct proper thermal design for engines to ensure reliable engine firing and
in-orbit storage. Generally electric heating (auxiliary thermal multi-layer) was used
to maintain the temperature of valves and injector with 5~15 °C for low temperature.
The thermal isolation of engines was used to maintain the temperature of valves lower
than 80 °C, such as titanium alloy materials with low heat conductivity, hollowed-out
structure to increase heat resistance and non-metal between valves and injector.
8.3.5 Long-Term Storage Environment on Lunar Surface
After the lunar lander was landed on lunar surface, the propulsion subsystem finishes
its job, but there was still remnant propellant and pressurized tanks including gas tanks
and propellant tanks. During long term operation, the propulsion subsystem along
with the lunar lander would experience alternation of lunar daytime and night where
there might be some safety risks. So the remnant propellant and pressurized gas
should be depleted. Generally, the propellant was depleted by engines firing, while
pressurized gas was depleted by directly venting outside. In order to avoid large
8 Propulsion Technology of Lunar Lander
was relatively much lower and not necessary to be considered. For large-scale, heavy
and high load components such as propellant tank, gas tank, orbit control engine and
etc., the pressure bearing should be satisfied, as well as mechanical environment in
launch phase, stiffness and strength of the lunar lander, otherwise there might be
structural deformation, instability and even broken due to insufficient stiffness or
strength.
For gas or liquid propellant in propulsion subsystem, there were requirements for
temperature condition of individual components in order to prevent liquid propellant
freezing in low temperature, vaporization in high temperature, pressure dramatic
rise, propellant decomposition and even explosion, especially for components
outside the lunar lander like engines, pipelines, valves, and even tanks, gas tanks
which were directly exposed (outside environment: high temperature can be more
than 150 °C in sun light, low temperature can be lower than −100 °C in the shadow).
In order to ensure reliable work of subsystem components, it was necessary to
control the temperature of individual components by thermal design. Generally, the
temperature range of components for liquid such as pipelines, tanks, valves, engines
should be 0~40 °C, while the temperature range of components for gas shall be −
30~70 °C. For the engines/nozzles exposed outside the lunar lander experiencing the
high/low temperature alternation which was much less than the temperature range
of radiation-cooling nozzle, it had almost no impact on nozzle materials (nozzle
is made of niobium-hafnium, niobium-tungsten, rhenium-iridium, carbon/carbon,
carbon/carborundum with high temperature anti oxidizing coatings). It should be
especially emphasized that external high/low temperature can transfer heat to engine
head through nozzle, which might lead to temperature rise or decline in engine head
and valves. In severe low temperature propellant in valves could be frozen with deflagration in cold starting. The high temperature might lead to propellant vaporization
which had impact on normal opening of valves and engine firing. So it was necessary
to conduct proper thermal design for engines to ensure reliable engine firing and
in-orbit storage. Generally electric heating (auxiliary thermal multi-layer) was used
to maintain the temperature of valves and injector with 5~15 °C for low temperature.
The thermal isolation of engines was used to maintain the temperature of valves lower
than 80 °C, such as titanium alloy materials with low heat conductivity, hollowed-out
structure to increase heat resistance and non-metal between valves and injector.
8.3.5 Long-Term Storage Environment on Lunar Surface
After the lunar lander was landed on lunar surface, the propulsion subsystem finishes
its job, but there was still remnant propellant and pressurized tanks including gas tanks
and propellant tanks. During long term operation, the propulsion subsystem along
with the lunar lander would experience alternation of lunar daytime and night where
there might be some safety risks. So the remnant propellant and pressurized gas
should be depleted. Generally, the propellant was depleted by engines firing, while
pressurized gas was depleted by directly venting outside. In order to avoid large