92
3 System Design of Lunar Lander
When the footpad touches lunar surface, the +X axis of lunar lander was nearly
vertical to lunar surface while the +Z axis was oriented to the local north. The
telemetry of lunar surface sensor was transmitted back to ground station as an
indicator of soft landing.
3.8.4 Downloading of Descent Images
Lunar lander should be able to download images taken by descent camera during
powered descent so images of lunar surface could be obtained for ground operation
as soon as possible. The images of descent camera were used only for display, which
would not be used for powered descent control. After safe landing, all images taken
by descent camera could be downloaded through directional telecommunication
channel.
3.9 Analysis and Simulation of Landing Stability
For lunar lander, the indicator of safe landing was that lunar lander was landed stably
on lunar surface without turn over or sink, the stable attitude was maintained and there
was no damage to onboard equipments caused by landing impact. Therefore analysis
of landing stability should be performed for detail design of lunar lander, initial
condition of soft landing and design of landing cushion mechanism with mechanical
property and terrain of lunar surface. The sensitivity analysis of all factors should be
performed to find the worst case in order to cover all possible condition in flight.
The influential factors for landing stability of lunar lander included features of
lunar lander, initial condition of soft landing and lunar environment. The features of
lunar lander include property of mass and moment of inertia, landing cushion features
of mechanism and geometry parameters. The initial condition of soft landing included
vertical velocity, horizontal velocity and attitude. The lunar environment includes
mechanic property, slope, distribution of impact pits and rocks of lunar surface.
In order to obtain probability of stable landing, those influential factors should be
analyzed for landing stability by Monte Carlo simulation of different combinations.
Thus the probability statistical model of stable landing should be established.
The impact response during soft landing, attenuation stroke and attitude after
landing could be obtained to evaluate landing stability by establishing dynamic model
of lunar lander, generating random lunar terrain and analyzing landing dynamics
process under different combinations of initial condition [10].
In order to obtain quantitative indicator of landing stability, the criterion of stability
could be given based on method of minimum stable distance. At first, concepts of turn
over line and safe line are given as shown in Figs. 3.29 and 3.30. The turn over line
was the closed curve that the line between centers of adjacent footpad is projected
on horizontal plane as black frame shown in Fig. 3.30. The safe line was the closed
3 System Design of Lunar Lander
When the footpad touches lunar surface, the +X axis of lunar lander was nearly
vertical to lunar surface while the +Z axis was oriented to the local north. The
telemetry of lunar surface sensor was transmitted back to ground station as an
indicator of soft landing.
3.8.4 Downloading of Descent Images
Lunar lander should be able to download images taken by descent camera during
powered descent so images of lunar surface could be obtained for ground operation
as soon as possible. The images of descent camera were used only for display, which
would not be used for powered descent control. After safe landing, all images taken
by descent camera could be downloaded through directional telecommunication
channel.
3.9 Analysis and Simulation of Landing Stability
For lunar lander, the indicator of safe landing was that lunar lander was landed stably
on lunar surface without turn over or sink, the stable attitude was maintained and there
was no damage to onboard equipments caused by landing impact. Therefore analysis
of landing stability should be performed for detail design of lunar lander, initial
condition of soft landing and design of landing cushion mechanism with mechanical
property and terrain of lunar surface. The sensitivity analysis of all factors should be
performed to find the worst case in order to cover all possible condition in flight.
The influential factors for landing stability of lunar lander included features of
lunar lander, initial condition of soft landing and lunar environment. The features of
lunar lander include property of mass and moment of inertia, landing cushion features
of mechanism and geometry parameters. The initial condition of soft landing included
vertical velocity, horizontal velocity and attitude. The lunar environment includes
mechanic property, slope, distribution of impact pits and rocks of lunar surface.
In order to obtain probability of stable landing, those influential factors should be
analyzed for landing stability by Monte Carlo simulation of different combinations.
Thus the probability statistical model of stable landing should be established.
The impact response during soft landing, attenuation stroke and attitude after
landing could be obtained to evaluate landing stability by establishing dynamic model
of lunar lander, generating random lunar terrain and analyzing landing dynamics
process under different combinations of initial condition [10].
In order to obtain quantitative indicator of landing stability, the criterion of stability
could be given based on method of minimum stable distance. At first, concepts of turn
over line and safe line are given as shown in Figs. 3.29 and 3.30. The turn over line
was the closed curve that the line between centers of adjacent footpad is projected
on horizontal plane as black frame shown in Fig. 3.30. The safe line was the closed