8.4 Propulsion Subsystem Design [5–7]
285
and light weight composite wrapping gas tank became a prevail tendency. Gas tank
operation pressure reaches 60 MPa and the gas tank mass and size were effectively
reduced. For example, two high pressure composite wrapping gas tanks with 100 L
volume for a single one and pressure as high as 35 MPa with T1000 carbon fiber
wrapped and seamless aluminum insider liner, were installed on the Chang’E-3 lunar
lander propulsion subsystem.
8.4.3 Design of Propellant Feed System [4]
1. Design of Pressurized Gas Feed and Management
The deviation of nominal thrust of orbit control engine should be no more than
3% and the structural mass restriction was stringent for the lunar lander propulsion
subsystem. Blow-down system couldn’t satisfy the requirements. The gas pressurization system with regulated pressure could ensure thrust of orbit control engine
with precision of 1%. For precisely control of mixture ratio, generally only one regulator was used (regulators can also be set in serials or parallel with consideration
of regulator failure) to ensures equal pressure of two different propellant tanks by
simultaneous pressurization. For surface tension tank, check valves were needed to
prevent unexpected mixing of two propellants or its vapor in gas system. For metal
diaphragm tank, check valves were not necessary and elimination of them can avoid
gas pressure deviation caused by flow resistance and low frequency vibration due
to gas flow in check valves. Because the tank pressure might be over pressurized if
there was regulator lock up pressure rise under non-flow conditions, the latch valves
were installed at upstream of regulators to realize overpressure regulation. When
overpressure occurs, the latch valve would automatically shut down and cut off high
pressure gas feed. After the pressure recovers, the latch valve would automatically
open again and restore gas feed. To avoid tank rapid overpressure caused by regulator sealing failure and valve rod stuck, the pressure relief valves with automatic
opening and venting under over pressurized condition were installed at downstream
of regulators to release pressure and shut-off when the pressure recovered to avoid
continuous vent.
For fill and vent of gas tanks, leak test and condition monitoring, fill and vent
valves, test interface, pressure and temperature sensors should be configured.
After landing, it was specially required for propulsion subsystem to conduct depletion to vent completely all residual propellant and gas. Generally, a pair of attitude
control thrusters fired simultaneously to deplete residual propellant and the pressurized gas was directly vented by solenoid valve or pyro valve at downstream of
pressure regulator till the pressure in propellant and gas tank dropped to 0 MPa.
The pressurized gas line of the Chang’E-3 lunar lander propulsion subsystem
were configured with 2 high pressure composite wrapped gas tanks for storing 100 L,
35 MPa pressurized Helium gas, feeding simultaneously through a large flow rate
285
and light weight composite wrapping gas tank became a prevail tendency. Gas tank
operation pressure reaches 60 MPa and the gas tank mass and size were effectively
reduced. For example, two high pressure composite wrapping gas tanks with 100 L
volume for a single one and pressure as high as 35 MPa with T1000 carbon fiber
wrapped and seamless aluminum insider liner, were installed on the Chang’E-3 lunar
lander propulsion subsystem.
8.4.3 Design of Propellant Feed System [4]
1. Design of Pressurized Gas Feed and Management
The deviation of nominal thrust of orbit control engine should be no more than
3% and the structural mass restriction was stringent for the lunar lander propulsion
subsystem. Blow-down system couldn’t satisfy the requirements. The gas pressurization system with regulated pressure could ensure thrust of orbit control engine
with precision of 1%. For precisely control of mixture ratio, generally only one regulator was used (regulators can also be set in serials or parallel with consideration
of regulator failure) to ensures equal pressure of two different propellant tanks by
simultaneous pressurization. For surface tension tank, check valves were needed to
prevent unexpected mixing of two propellants or its vapor in gas system. For metal
diaphragm tank, check valves were not necessary and elimination of them can avoid
gas pressure deviation caused by flow resistance and low frequency vibration due
to gas flow in check valves. Because the tank pressure might be over pressurized if
there was regulator lock up pressure rise under non-flow conditions, the latch valves
were installed at upstream of regulators to realize overpressure regulation. When
overpressure occurs, the latch valve would automatically shut down and cut off high
pressure gas feed. After the pressure recovers, the latch valve would automatically
open again and restore gas feed. To avoid tank rapid overpressure caused by regulator sealing failure and valve rod stuck, the pressure relief valves with automatic
opening and venting under over pressurized condition were installed at downstream
of regulators to release pressure and shut-off when the pressure recovered to avoid
continuous vent.
For fill and vent of gas tanks, leak test and condition monitoring, fill and vent
valves, test interface, pressure and temperature sensors should be configured.
After landing, it was specially required for propulsion subsystem to conduct depletion to vent completely all residual propellant and gas. Generally, a pair of attitude
control thrusters fired simultaneously to deplete residual propellant and the pressurized gas was directly vented by solenoid valve or pyro valve at downstream of
pressure regulator till the pressure in propellant and gas tank dropped to 0 MPa.
The pressurized gas line of the Chang’E-3 lunar lander propulsion subsystem
were configured with 2 high pressure composite wrapped gas tanks for storing 100 L,
35 MPa pressurized Helium gas, feeding simultaneously through a large flow rate