8.4 Propulsion Subsystem Design [5–7]
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subsystem of Apollo lunar module and the engine with throttling ratio of 5:1 was
applied in propulsion subsystem of the Chang’E-3 lunar lander.
Combined throttling for bi-propellant orbit control engine generally applied
“stepping motor and pintle” mechanism, which drove the variable pintle of
cavitating-venturi and injector to modulate flux and pressure drop synchronously.
Design of bi-propellant orbit control engine generally included 3 types of cooling:
radiation cooling, regenerative cooling and ablative cooling. For large ratio throttling
engine, because the propellant flux varied widely, it was difficult to maintain reliable
cooling over all operation regime due to wide variation of coolant for regenerative cooling. For the orbit control engine which was used for LTO, circumlunar
orbit and powered descent with long lifetime, the disadvantages of ablative cooling
included short lifetime, unstable performance (uncertainty in ablation), heavy structural mass and etc., which made it suitable for short term scenario. Therefore radiation
cooling was more suitable. The common materials used for engine chamber of radiation cooling engine, such as niobium, rhenium-iridium, platinum-rhodium alloy and
carbon fiber ceramics materials, were capable of resisting high temperature, oxidation and erosion. For example, the niobium-tungsten alloy was used in thrust chamber
of the 7500 N throttling engine on the Chang’E-3 lunar lander.
2. Propellant Tank
Propellant tank was used for storing propellant (oxidizer, fuel) required for
orbit/attitude control engine operation, managing propellant in zero gravity condition and supplying propellant with capabilities of pressure-bearing, load-bearing and
long term compatibility. There were generally three types of propellant tank for bipropellant propulsion subsystem including surface tension tank based on titanium
alloy (full management or local management), metal diaphragm with aluminum alloy
and fluoro-plastics bladder, whose technology readiness was all good. For the lunar
lander propulsion subsystem, aluminum alloy diaphragm tank had advantages such
as easily realizing large flux, sloshing free, unconstrained by accelerate direction,
long term propellant compatibility, simplicity of gas line (no need using check valve
for isolation) and etc. The main disadvantage was low strength of aluminum alloy
which might cause heavier structure, and limited overturn times of diaphragm (actually once, overturn capabilities no less than 3 times). Currently, the approaches to
solved heavy weight of aluminum alloy diaphragm tank include: (1) application
of high-strength aluminum-scandium alloy instead of traditional aluminum alloy to
make tank shell, (2) wrapping with carbon fiber to strengthen tank shell structure, (3)
using high-strength titanium alloy diaphragm tank. The key part of metal diaphragm
tank was internal metal diaphragm. In order to ensure regular deformation and reliable overturn of diaphragm, it was necessary to apply variable thickness and curvature
design. For example, the design of aluminum insider liner and carbon fiber wrapping was applied to reduce weight in propellant tank of propulsion subsystem of the
Chang’E-3 lunar lander. Fully welded aluminum inside liner with good propellant
compatibility was used to seal pressurized gas and propellant, and bear load (propellant mass, acceleration, vibration and etc.). Carbon fiber with multi-direction alternative wrapping was capable of withstanding tank inner pressure. Specially configured
291
subsystem of Apollo lunar module and the engine with throttling ratio of 5:1 was
applied in propulsion subsystem of the Chang’E-3 lunar lander.
Combined throttling for bi-propellant orbit control engine generally applied
“stepping motor and pintle” mechanism, which drove the variable pintle of
cavitating-venturi and injector to modulate flux and pressure drop synchronously.
Design of bi-propellant orbit control engine generally included 3 types of cooling:
radiation cooling, regenerative cooling and ablative cooling. For large ratio throttling
engine, because the propellant flux varied widely, it was difficult to maintain reliable
cooling over all operation regime due to wide variation of coolant for regenerative cooling. For the orbit control engine which was used for LTO, circumlunar
orbit and powered descent with long lifetime, the disadvantages of ablative cooling
included short lifetime, unstable performance (uncertainty in ablation), heavy structural mass and etc., which made it suitable for short term scenario. Therefore radiation
cooling was more suitable. The common materials used for engine chamber of radiation cooling engine, such as niobium, rhenium-iridium, platinum-rhodium alloy and
carbon fiber ceramics materials, were capable of resisting high temperature, oxidation and erosion. For example, the niobium-tungsten alloy was used in thrust chamber
of the 7500 N throttling engine on the Chang’E-3 lunar lander.
2. Propellant Tank
Propellant tank was used for storing propellant (oxidizer, fuel) required for
orbit/attitude control engine operation, managing propellant in zero gravity condition and supplying propellant with capabilities of pressure-bearing, load-bearing and
long term compatibility. There were generally three types of propellant tank for bipropellant propulsion subsystem including surface tension tank based on titanium
alloy (full management or local management), metal diaphragm with aluminum alloy
and fluoro-plastics bladder, whose technology readiness was all good. For the lunar
lander propulsion subsystem, aluminum alloy diaphragm tank had advantages such
as easily realizing large flux, sloshing free, unconstrained by accelerate direction,
long term propellant compatibility, simplicity of gas line (no need using check valve
for isolation) and etc. The main disadvantage was low strength of aluminum alloy
which might cause heavier structure, and limited overturn times of diaphragm (actually once, overturn capabilities no less than 3 times). Currently, the approaches to
solved heavy weight of aluminum alloy diaphragm tank include: (1) application
of high-strength aluminum-scandium alloy instead of traditional aluminum alloy to
make tank shell, (2) wrapping with carbon fiber to strengthen tank shell structure, (3)
using high-strength titanium alloy diaphragm tank. The key part of metal diaphragm
tank was internal metal diaphragm. In order to ensure regular deformation and reliable overturn of diaphragm, it was necessary to apply variable thickness and curvature
design. For example, the design of aluminum insider liner and carbon fiber wrapping was applied to reduce weight in propellant tank of propulsion subsystem of the
Chang’E-3 lunar lander. Fully welded aluminum inside liner with good propellant
compatibility was used to seal pressurized gas and propellant, and bear load (propellant mass, acceleration, vibration and etc.). Carbon fiber with multi-direction alternative wrapping was capable of withstanding tank inner pressure. Specially configured