15.4 Hovering, Obstacle Avoidance and Slow Descent Tests
497
descending, the height and velocity of the lunar lander were respectively
measured by laser ranging sensor and microwave ranging and velocity sensors.
The test site should provide condition for sensors and simulate the reflection
characteristics of the laser and microwave on lunar surface.
(6) The choice of test facilities and test windows should not interfere with the test
system.
In order to satisfy above constraints, special attitude tracking system and translational
motion tracking system should be designed to simulate free flight conditions on orbit,
and simulation landing field should be designed to simulate lunar terrain topography,
reflection characteristics of lunar surface, and illumination characteristics. Besides,
it was also necessary to build a test gantry system to provide adequate support and
test space.
15.4.3 Design of Test System
In the hovering, obstacle avoidance and slow descending tests, it was necessary
to simulate the force state, motion DOF, lunar terrain, reflection characteristics of
lunar surface, coordination between GNC subsystem and propulsion subsystem,
and autonomous navigation control algorithms. The entire system was composed
of the lunar lander test model subsystem, gantry subsystem, simulated lunar surface
subsystem and test control subsystem.
1. Force State and Translational Motion Simulation
The gravity environment on the ground was different from that of lunar surface. The
maximum output thrust of the engine was less than the weight of the lunar lander test
model, so the lunar lander test model could not be hovered. Therefore, in the design
of the test system, simulation of the force state of the lunar lander test model should
be considered at first, which was also one of the cores of the test system.
The test gantry was built up. The lunar lander test model was lifted by a rope,
which would balance part of weight of the lunar lander test model by control the rope
to maintain a constant tension with servo control system in the test. With throttling of
the engine output thrust, the resultant force on the lunar lander test model in the test
would be consistent with that in lunar soft landing, so as to simulate the kinematics
characteristics of the lunar lander in real landing process. The rope could also be able
to follow horizontally. In the test, the rope would follow up the horizontal motion of
the lunar lander test model in real time. The direction of rope tension on the lunar
lander test model should always be vertical and up, so as to avoid the horizontal
component force of the rope tension to interfere the test when the lunar lander test
model was moving horizontally. The test gantry structure is shown in Fig. 15.8.
2. Simulation of Attitude DOF
In order to simulate the attitude DOF of the lunar lander, a gimbal spreader system
should be designed. The spreader was connected to the lunar lander test model by
497
descending, the height and velocity of the lunar lander were respectively
measured by laser ranging sensor and microwave ranging and velocity sensors.
The test site should provide condition for sensors and simulate the reflection
characteristics of the laser and microwave on lunar surface.
(6) The choice of test facilities and test windows should not interfere with the test
system.
In order to satisfy above constraints, special attitude tracking system and translational
motion tracking system should be designed to simulate free flight conditions on orbit,
and simulation landing field should be designed to simulate lunar terrain topography,
reflection characteristics of lunar surface, and illumination characteristics. Besides,
it was also necessary to build a test gantry system to provide adequate support and
test space.
15.4.3 Design of Test System
In the hovering, obstacle avoidance and slow descending tests, it was necessary
to simulate the force state, motion DOF, lunar terrain, reflection characteristics of
lunar surface, coordination between GNC subsystem and propulsion subsystem,
and autonomous navigation control algorithms. The entire system was composed
of the lunar lander test model subsystem, gantry subsystem, simulated lunar surface
subsystem and test control subsystem.
1. Force State and Translational Motion Simulation
The gravity environment on the ground was different from that of lunar surface. The
maximum output thrust of the engine was less than the weight of the lunar lander test
model, so the lunar lander test model could not be hovered. Therefore, in the design
of the test system, simulation of the force state of the lunar lander test model should
be considered at first, which was also one of the cores of the test system.
The test gantry was built up. The lunar lander test model was lifted by a rope,
which would balance part of weight of the lunar lander test model by control the rope
to maintain a constant tension with servo control system in the test. With throttling of
the engine output thrust, the resultant force on the lunar lander test model in the test
would be consistent with that in lunar soft landing, so as to simulate the kinematics
characteristics of the lunar lander in real landing process. The rope could also be able
to follow horizontally. In the test, the rope would follow up the horizontal motion of
the lunar lander test model in real time. The direction of rope tension on the lunar
lander test model should always be vertical and up, so as to avoid the horizontal
component force of the rope tension to interfere the test when the lunar lander test
model was moving horizontally. The test gantry structure is shown in Fig. 15.8.
2. Simulation of Attitude DOF
In order to simulate the attitude DOF of the lunar lander, a gimbal spreader system
should be designed. The spreader was connected to the lunar lander test model by