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8 Propulsion Technology of Lunar Lander
regulator to 4 metal diaphragm tanks (2 for oxidizer and 2 for fuel). And high pressure latch valve and relief valve were configured as double safety methods for tank
overpressure management.
2. Propellant Storage and Management
Design of propellant storage and management consisted of propellant fill and vent
method, storage and safety isolation from downstream pipeline, liquid management
under zero-gravity environment, propellant feeding and condition monitoring and
etc. Design of propellant storage and management was up to tank type. For surface
tension tank with pressurized filling, tank outlet was safely isolated by latch valve
or pyro valve. For diaphragm tank, due to its closed liquid cavity, propellant filling
could be realized by evacuation filling and tank outlet can be safely isolated by
diaphragm valve, latch valve or pyro valve. When it was isolated by diaphragm
valve without electric control, the valve would be opened by tank pressurization.
When the burst pressure of diaphragm valve was designed, it should be considered including saturated vapor pressure, liquid level, flight overload, burst pressure
deviation, tank expulsion pressure and etc. to ensure not only reliable isolation of
diaphragm prior to tank pressurization, but also effective burst after tank pressurization. Fill and vent valves, pressure and temperature sensors should be configured to
monitor tank pressure, temperature and propellant filling. For example, there were
4 identical spherical metal diaphragm tanks (2 for oxidizer and 2 for fuel) in the
Chang’E-3 lunar lander propulsion subsystem. The pressurized gas cavity was separated from propellant cavity by metal diaphragm with special profile, while the
metal diaphragm was compressed tightly on liquid by pressurized helium gas metal
diaphragm tightly and deformed to expulse the propellant in the propellant tank.
Because the metal diaphragm deformed under certain pressure difference and the
force applied on propellant was much larger than sloshing force, the propellant slosh
could be eliminated and there was not constrain by overload direction, which made
it more suitable for complicated overload environment of the lunar lander.
3. Propellant Feed and Management
Design of propellant feed and management consisted of orbit and attitude control
engine management, and propellant feed system monitoring. Generally in order to
minimize the interaction between orbit and attitude control engines, latch valves
were used for orbit and attitude control engine to operate independently. For attitude
control feed pipelines, solenoid latch valves were used directly, while solenoid or
pneumatic latch valves can be used for orbit control feed pipeline depending on the
thrust-level of engines. If the thrust was greater than 3000 N, the pneumatic latch valve
was generally used because the solenoid valve was heavier. Because of constraints
of structural mass and size for the lunar lander, basically there was only one orbit
control engine and two branches for attitude control thrusters, where single branch
could be isolated under failure conditions. For example, there were one 7500 N orbit
control engine and 28 attitude control thrusters, while the orbit control engine was
managed by 4 pneumatic latch valves and attitude control thrusters were managed
by 8 electromagnetic latch valves divided into A/B two branches according to the
8 Propulsion Technology of Lunar Lander
regulator to 4 metal diaphragm tanks (2 for oxidizer and 2 for fuel). And high pressure latch valve and relief valve were configured as double safety methods for tank
overpressure management.
2. Propellant Storage and Management
Design of propellant storage and management consisted of propellant fill and vent
method, storage and safety isolation from downstream pipeline, liquid management
under zero-gravity environment, propellant feeding and condition monitoring and
etc. Design of propellant storage and management was up to tank type. For surface
tension tank with pressurized filling, tank outlet was safely isolated by latch valve
or pyro valve. For diaphragm tank, due to its closed liquid cavity, propellant filling
could be realized by evacuation filling and tank outlet can be safely isolated by
diaphragm valve, latch valve or pyro valve. When it was isolated by diaphragm
valve without electric control, the valve would be opened by tank pressurization.
When the burst pressure of diaphragm valve was designed, it should be considered including saturated vapor pressure, liquid level, flight overload, burst pressure
deviation, tank expulsion pressure and etc. to ensure not only reliable isolation of
diaphragm prior to tank pressurization, but also effective burst after tank pressurization. Fill and vent valves, pressure and temperature sensors should be configured to
monitor tank pressure, temperature and propellant filling. For example, there were
4 identical spherical metal diaphragm tanks (2 for oxidizer and 2 for fuel) in the
Chang’E-3 lunar lander propulsion subsystem. The pressurized gas cavity was separated from propellant cavity by metal diaphragm with special profile, while the
metal diaphragm was compressed tightly on liquid by pressurized helium gas metal
diaphragm tightly and deformed to expulse the propellant in the propellant tank.
Because the metal diaphragm deformed under certain pressure difference and the
force applied on propellant was much larger than sloshing force, the propellant slosh
could be eliminated and there was not constrain by overload direction, which made
it more suitable for complicated overload environment of the lunar lander.
3. Propellant Feed and Management
Design of propellant feed and management consisted of orbit and attitude control
engine management, and propellant feed system monitoring. Generally in order to
minimize the interaction between orbit and attitude control engines, latch valves
were used for orbit and attitude control engine to operate independently. For attitude
control feed pipelines, solenoid latch valves were used directly, while solenoid or
pneumatic latch valves can be used for orbit control feed pipeline depending on the
thrust-level of engines. If the thrust was greater than 3000 N, the pneumatic latch valve
was generally used because the solenoid valve was heavier. Because of constraints
of structural mass and size for the lunar lander, basically there was only one orbit
control engine and two branches for attitude control thrusters, where single branch
could be isolated under failure conditions. For example, there were one 7500 N orbit
control engine and 28 attitude control thrusters, while the orbit control engine was
managed by 4 pneumatic latch valves and attitude control thrusters were managed
by 8 electromagnetic latch valves divided into A/B two branches according to the