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8 Propulsion Technology of Lunar Lander
mechanical environmental conditions for propulsion subsystem and its components
as well as comprehensive verification tests, especially for large-scale, heavy mass
components such as propellant tank, gas tank, orbit control engine and etc. Due to its
complication, the pipeline should not only be configured and fixed appropriately, but
also be kept enough space for deformation of each part respectively to avoid pipeline
broken caused by rigid constraints. The whole propulsion subsystem should be tested
and verified under conditions simulated the flight environment as real as possible
(if necessary, under more serious conditions) in order to satisfy flight mechanical
environment requirements during launch.
3) Environment on orbit
There were environmental conditions including vacuum, zero gravity, temperature
alternation and space radiation environment on orbit. The vacuum environment had
no influence on propulsion system operation under internal pressure, but engine
vacuum firing and cooling capability should be considered. At the same time, for
moving parts exposed under vacuum environment, “vacuum welding” issue between
metals should also be considered, which could be solved by remaining clearance,
different metals, surface coating and so on. The zero gravity environment was an
important factor when the propellant tank for space propulsion system was designed
to ensure reliable management of liquid propellant inside tanks and avoid output of
liquid with gas trapping. The methods for management of liquid propellant under
zero gravity could be classified into two types: gas liquid mixed type and gas liquid
physical isolation type. As an example of gas liquid mixed type, the surface tension
tank and centrifugal tank (for spinning stabilization spacecraft) were designed to
collect and expel liquid by surface tension effect. As an example of gas liquid physical isolation type, the metal diaphragm, non-metal bladder and piston tanks were
designed to isolate pressurized gas from liquid propellant by metal diaphragm or nonmetal bladder. For hypergolic bi-propellant propulsion subsystems, surface tension
and metal diaphragm management tanks were generally used. When the propellant
tank of the lunar lander was designed, it was necessary to consider large flux and
wide range of flux variation of propellant (for orbit control engine with large flux
and throttling ratio), lateral overload during soft-landing, liquid slosh, anti-vortex in
EOL (end of life) large flux and etc. in order to determine the propellant management method. For example, the metal diaphragm tank was applied to isolate gas from
liquid and eliminate uncertainty caused by propellant compatibility, slosh, adaptability, EOL disposal vortex and etc. for propulsion system of the Chang’E-3 lunar
lander. Space radiation environment including ultraviolet rays, atomic oxygen, and
charged ions, had significant impact on electronic devices of propulsion subsystem.
Therefore it was necessary to strengthen anti-radiation design, especially anti-Single
Event Effect. At the same time, it was important to avoid application of non-metals
sensitive to ultraviolet irradiation, atomic oxygen erosion.
2. Propellant Load and Pressurized Gas Volume
Propellant load was determined by many factors such as specific impulse, orbit
control, attitude control, tank expulsion efficiency, remnant propellant, mix ratio
8 Propulsion Technology of Lunar Lander
mechanical environmental conditions for propulsion subsystem and its components
as well as comprehensive verification tests, especially for large-scale, heavy mass
components such as propellant tank, gas tank, orbit control engine and etc. Due to its
complication, the pipeline should not only be configured and fixed appropriately, but
also be kept enough space for deformation of each part respectively to avoid pipeline
broken caused by rigid constraints. The whole propulsion subsystem should be tested
and verified under conditions simulated the flight environment as real as possible
(if necessary, under more serious conditions) in order to satisfy flight mechanical
environment requirements during launch.
3) Environment on orbit
There were environmental conditions including vacuum, zero gravity, temperature
alternation and space radiation environment on orbit. The vacuum environment had
no influence on propulsion system operation under internal pressure, but engine
vacuum firing and cooling capability should be considered. At the same time, for
moving parts exposed under vacuum environment, “vacuum welding” issue between
metals should also be considered, which could be solved by remaining clearance,
different metals, surface coating and so on. The zero gravity environment was an
important factor when the propellant tank for space propulsion system was designed
to ensure reliable management of liquid propellant inside tanks and avoid output of
liquid with gas trapping. The methods for management of liquid propellant under
zero gravity could be classified into two types: gas liquid mixed type and gas liquid
physical isolation type. As an example of gas liquid mixed type, the surface tension
tank and centrifugal tank (for spinning stabilization spacecraft) were designed to
collect and expel liquid by surface tension effect. As an example of gas liquid physical isolation type, the metal diaphragm, non-metal bladder and piston tanks were
designed to isolate pressurized gas from liquid propellant by metal diaphragm or nonmetal bladder. For hypergolic bi-propellant propulsion subsystems, surface tension
and metal diaphragm management tanks were generally used. When the propellant
tank of the lunar lander was designed, it was necessary to consider large flux and
wide range of flux variation of propellant (for orbit control engine with large flux
and throttling ratio), lateral overload during soft-landing, liquid slosh, anti-vortex in
EOL (end of life) large flux and etc. in order to determine the propellant management method. For example, the metal diaphragm tank was applied to isolate gas from
liquid and eliminate uncertainty caused by propellant compatibility, slosh, adaptability, EOL disposal vortex and etc. for propulsion system of the Chang’E-3 lunar
lander. Space radiation environment including ultraviolet rays, atomic oxygen, and
charged ions, had significant impact on electronic devices of propulsion subsystem.
Therefore it was necessary to strengthen anti-radiation design, especially anti-Single
Event Effect. At the same time, it was important to avoid application of non-metals
sensitive to ultraviolet irradiation, atomic oxygen erosion.
2. Propellant Load and Pressurized Gas Volume
Propellant load was determined by many factors such as specific impulse, orbit
control, attitude control, tank expulsion efficiency, remnant propellant, mix ratio