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11 Landing Gear Technology of Lunar Lander
(2) Radiation. The charged-particle radiation and ultraviolet radiation might significantly affect nonmetal materials such as rubber seal rings and adhesives, but
little on metals. For the landing gear mechanism, rubber seal rings and adhesives should not be exposed directly. Material of outer multi-layer insulation
should be good at anti-radiation and processed by surface coating.
(3) Vacuum. The polymeric material was prone to sublimation and decomposition
under vacuum, which might result in degradation of material performance.
In order to avoid sublimation and decomposition of material under vacuum,
metallic material was better choice for parts of landing gear mechanism. For the
parts like footpad and adhesive of aluminum honeycomb, materials that had
been successfully applied in space missions are preferred. Moreover, under
ultrahigh vacuum condition, the joints of mechanism might suffer from cold
welding at a certain pressure and fail. Effective measures were lubrication for
joint surfaces and limiting the friction resistant force into an acceptable range.
(4) Gravity. Acceleration of lunar gravity is about one-sixth of Earth gravity. The
lower gravity may lead to turning over during landings. This gravity difference
should be sufficiently considered in design and ground test of the landing gear
mechanism.
(5) Lunar terrain of landing zone. It included slope of lunar surface, dimension and
distribution of pit and rock, and etc. The large slope might cause declination
or even turnover of the lunar lander. Pit and rock can significantly affect the
landing stability.
(6) Mechanical properties of landing surface and lunar dust. Mechanical properties
of landing surface referred to bearing strength and coefficient of friction under
variable dynamic impact velocity. Different properties led to different bearing
strength for the footpad on landing surface and different cushion performance
in landing process. Before landing, the retro rocket engine was usually applied
to decrease touchdown velocity. Therefore, the dust might be raised by the
engine plume when the lunar lander approached the dusty surface. The dust
adhering to joint surfaces had adverse effect on movement of mechanism.
Measures such as coated protection for the movable parts should be designed,
which could be implemented together with thermal control.
(7) Thermal environment. There were thermal effects on the lunar lander during
LTO and powered descent. The mechanical parts of relative movements should
be in same kind of material or materials with approximate expansion coefficient
to make sure that the fit grade of joint surfaces would not change, so as to adapt
such environment. Meanwhile it was suggested to select the cushion method
insensitive to temperature. The proper thermal control should be applied if
necessary. Moreover, the landing gear mechanism was generally installed on
the bottom of the lunar lander, which was close to the main engine. Therefore, special attention should be paid to effect of engine plume on the landing
gear mechanism to ensure sufficient cushion performance under such thermal
environment.
11 Landing Gear Technology of Lunar Lander
(2) Radiation. The charged-particle radiation and ultraviolet radiation might significantly affect nonmetal materials such as rubber seal rings and adhesives, but
little on metals. For the landing gear mechanism, rubber seal rings and adhesives should not be exposed directly. Material of outer multi-layer insulation
should be good at anti-radiation and processed by surface coating.
(3) Vacuum. The polymeric material was prone to sublimation and decomposition
under vacuum, which might result in degradation of material performance.
In order to avoid sublimation and decomposition of material under vacuum,
metallic material was better choice for parts of landing gear mechanism. For the
parts like footpad and adhesive of aluminum honeycomb, materials that had
been successfully applied in space missions are preferred. Moreover, under
ultrahigh vacuum condition, the joints of mechanism might suffer from cold
welding at a certain pressure and fail. Effective measures were lubrication for
joint surfaces and limiting the friction resistant force into an acceptable range.
(4) Gravity. Acceleration of lunar gravity is about one-sixth of Earth gravity. The
lower gravity may lead to turning over during landings. This gravity difference
should be sufficiently considered in design and ground test of the landing gear
mechanism.
(5) Lunar terrain of landing zone. It included slope of lunar surface, dimension and
distribution of pit and rock, and etc. The large slope might cause declination
or even turnover of the lunar lander. Pit and rock can significantly affect the
landing stability.
(6) Mechanical properties of landing surface and lunar dust. Mechanical properties
of landing surface referred to bearing strength and coefficient of friction under
variable dynamic impact velocity. Different properties led to different bearing
strength for the footpad on landing surface and different cushion performance
in landing process. Before landing, the retro rocket engine was usually applied
to decrease touchdown velocity. Therefore, the dust might be raised by the
engine plume when the lunar lander approached the dusty surface. The dust
adhering to joint surfaces had adverse effect on movement of mechanism.
Measures such as coated protection for the movable parts should be designed,
which could be implemented together with thermal control.
(7) Thermal environment. There were thermal effects on the lunar lander during
LTO and powered descent. The mechanical parts of relative movements should
be in same kind of material or materials with approximate expansion coefficient
to make sure that the fit grade of joint surfaces would not change, so as to adapt
such environment. Meanwhile it was suggested to select the cushion method
insensitive to temperature. The proper thermal control should be applied if
necessary. Moreover, the landing gear mechanism was generally installed on
the bottom of the lunar lander, which was close to the main engine. Therefore, special attention should be paid to effect of engine plume on the landing
gear mechanism to ensure sufficient cushion performance under such thermal
environment.