3.8 Design of Powered Descent and Soft Landing
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acceleration in appropriate direction was generated, the pitch angle relative to
lunar surface was adjusted to 9° and the yaw angle was adjusted reversely till
the height and velocity of lunar lander satisfied requirements of hovering.
(5) Hovering. The height relative to lunar surface was about 100 m. The major task
was to finely identify obstacles in landing site. The gravity of lunar lander was
compensated by thrust of throttlable engine and lunar lander was kept hovering
in order to observe landing site by 3-D imaging sensor to select safe landing
site.
The roll, pitch and yaw angle relative to lunar surface was adjusted to about 0°
during hovering.
(6) Obstacle avoiding. The height relative to lunar surface was from 100 m to 30 m.
The major task was to finely avoid obstacles and descent. According to relative
position of safe landing site given during hovering, lunar lander was descended
to the position above the safe landing site, while the descent velocity relative
to lunar surface was at predefined value and horizontal velocity is about zero.
The trajectory during obstacle avoiding was an oblique line toward landing
site.
The roll, pitch and yaw angle relative to lunar surface was adjusted to about 0°
during obstacle avoiding.
(7) Slow descent. The height relative to lunar surface was from about 30 m to the
height where the gamma sensor for engine shut off was triggered. The major
tasks were to ensure steady and slow descent of lunar lander and the control
accuracy of velocity and attitude satisfy requirements of soft landing. If the
gamma sensor for engine shut off failed, the lunar surface sensor might provide
backup signal for engine shut off.
The roll, pitch and yaw angle relative to lunar surface was adjusted to about 0°
during slow descent.
3.8.3 Landing Cushion
When lunar lander was landed on lunar surface, the footpad of landing legs touched
lunar surface at first. The ball joint could rotate freely to adapt lunar terrain. Then the
footpad pushed the inner tube of main pillar to slide relative to the outer tube. The
relative movement of inner tube to outer tube would compress aluminum honeycomb
to absorb impact energy for cushion. When the horizontal load exceeded the limit,
the two auxiliary pillars could provide cushion for both tension and compression.
The slender rod could implement tension attenuation. The aluminum honeycomb
could implement compression attenuation.
There were lunar surface sensors on footpad of landing legs. When the footpad
touched lunar surface, the signal of touching lunar surface was transferred to GNC
subsystem, which served as a backup method to shut off main engine in case of
failure of the gamma sensor for engine shut off.
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acceleration in appropriate direction was generated, the pitch angle relative to
lunar surface was adjusted to 9° and the yaw angle was adjusted reversely till
the height and velocity of lunar lander satisfied requirements of hovering.
(5) Hovering. The height relative to lunar surface was about 100 m. The major task
was to finely identify obstacles in landing site. The gravity of lunar lander was
compensated by thrust of throttlable engine and lunar lander was kept hovering
in order to observe landing site by 3-D imaging sensor to select safe landing
site.
The roll, pitch and yaw angle relative to lunar surface was adjusted to about 0°
during hovering.
(6) Obstacle avoiding. The height relative to lunar surface was from 100 m to 30 m.
The major task was to finely avoid obstacles and descent. According to relative
position of safe landing site given during hovering, lunar lander was descended
to the position above the safe landing site, while the descent velocity relative
to lunar surface was at predefined value and horizontal velocity is about zero.
The trajectory during obstacle avoiding was an oblique line toward landing
site.
The roll, pitch and yaw angle relative to lunar surface was adjusted to about 0°
during obstacle avoiding.
(7) Slow descent. The height relative to lunar surface was from about 30 m to the
height where the gamma sensor for engine shut off was triggered. The major
tasks were to ensure steady and slow descent of lunar lander and the control
accuracy of velocity and attitude satisfy requirements of soft landing. If the
gamma sensor for engine shut off failed, the lunar surface sensor might provide
backup signal for engine shut off.
The roll, pitch and yaw angle relative to lunar surface was adjusted to about 0°
during slow descent.
3.8.3 Landing Cushion
When lunar lander was landed on lunar surface, the footpad of landing legs touched
lunar surface at first. The ball joint could rotate freely to adapt lunar terrain. Then the
footpad pushed the inner tube of main pillar to slide relative to the outer tube. The
relative movement of inner tube to outer tube would compress aluminum honeycomb
to absorb impact energy for cushion. When the horizontal load exceeded the limit,
the two auxiliary pillars could provide cushion for both tension and compression.
The slender rod could implement tension attenuation. The aluminum honeycomb
could implement compression attenuation.
There were lunar surface sensors on footpad of landing legs. When the footpad
touched lunar surface, the signal of touching lunar surface was transferred to GNC
subsystem, which served as a backup method to shut off main engine in case of
failure of the gamma sensor for engine shut off.