8.3 Design Constraints and Analysis
279
disturbing force to the lunar lander by engine firing and pressurized gas venting, the
symmetrically distributed engines were simultaneously firing and shut down, as well
as symmetrically gas venting vent was set to eliminate and diminish disturbing force.
When the remnant propellant was depleted by engines firing, due to the difference
of two types of remnant propellant, depletion of all propellant at the same time
might not be possible. It was necessary to control the time of shut down of engines
by pressure variation during depletion, so as to avoid back flow of one propellant
to the engine heads and explosion. In addition, due to dramatic pressure variation
of propulsion subsystem when the propellant was depleted, it might lead to great
uncertainty in engine combustion with wild variation of chamber pressure, mixed
ratio and boundary film cooling, it was necessary to be verified by test in development
to ensure the engine safety in depletion.
8.4 Propulsion Subsystem Design [5–7]
8.4.1 Fundamental Design Conditions
1. Environmental Condition
1) Ground environment
(1) Environment temperature: The environment temperature should be principally
maintained at 20 ± 5 °C (if specially required, it could also be 12~20 °C), while
more attention should be paid on temperature in propellant filling facility and
launch vehicle fairing. When the balance was reached between the temperature
of propulsion subsystem and environment, it was necessary to maintain enough
safety ullage with no less than 3% of total volume of liquid cavity in propellant
tanks and pressure in gas tank lower than its maximal allowed pressure.
(2) Atmospheric pressure: In case of propellant filling with tank evacuation, the
tank shell should withstand ambient pressure (unnecessary for pressurized
filling). During launch phase, it was also possible for the tank to bear external
aerodynamic pressure. Therefore when the tank shell was designed, it was
required that the shell must have enough margin resistant from external pressure
with consideration of local atmospheric pressure level in launch site besides
requirement for internal pressure, especially for composite wrapping tank.
Generally, instability safety factor for external pressure should not be less than
5.0.
2) Flight environment during launch
The mechanical environments such as flight overload, vibration, impact and etc.
during launch were crucial to structure of propulsion subsystem. While the structure
and components bearing pressure of propulsion subsystem was designed, it was
necessary to conduct the analysis of strength, stiffness and stability according to
279
disturbing force to the lunar lander by engine firing and pressurized gas venting, the
symmetrically distributed engines were simultaneously firing and shut down, as well
as symmetrically gas venting vent was set to eliminate and diminish disturbing force.
When the remnant propellant was depleted by engines firing, due to the difference
of two types of remnant propellant, depletion of all propellant at the same time
might not be possible. It was necessary to control the time of shut down of engines
by pressure variation during depletion, so as to avoid back flow of one propellant
to the engine heads and explosion. In addition, due to dramatic pressure variation
of propulsion subsystem when the propellant was depleted, it might lead to great
uncertainty in engine combustion with wild variation of chamber pressure, mixed
ratio and boundary film cooling, it was necessary to be verified by test in development
to ensure the engine safety in depletion.
8.4 Propulsion Subsystem Design [5–7]
8.4.1 Fundamental Design Conditions
1. Environmental Condition
1) Ground environment
(1) Environment temperature: The environment temperature should be principally
maintained at 20 ± 5 °C (if specially required, it could also be 12~20 °C), while
more attention should be paid on temperature in propellant filling facility and
launch vehicle fairing. When the balance was reached between the temperature
of propulsion subsystem and environment, it was necessary to maintain enough
safety ullage with no less than 3% of total volume of liquid cavity in propellant
tanks and pressure in gas tank lower than its maximal allowed pressure.
(2) Atmospheric pressure: In case of propellant filling with tank evacuation, the
tank shell should withstand ambient pressure (unnecessary for pressurized
filling). During launch phase, it was also possible for the tank to bear external
aerodynamic pressure. Therefore when the tank shell was designed, it was
required that the shell must have enough margin resistant from external pressure
with consideration of local atmospheric pressure level in launch site besides
requirement for internal pressure, especially for composite wrapping tank.
Generally, instability safety factor for external pressure should not be less than
5.0.
2) Flight environment during launch
The mechanical environments such as flight overload, vibration, impact and etc.
during launch were crucial to structure of propulsion subsystem. While the structure
and components bearing pressure of propulsion subsystem was designed, it was
necessary to conduct the analysis of strength, stiffness and stability according to