15.4 Hovering, Obstacle Avoidance and Slow Descent Tests
495
15.4.2 Test Constraints and Methodology
In ground environment, the thrust of throttling engine could not balance weight of the
lunar lander, and it was difficult to satisfy the test requirements for control of velocity
and attitude of the lunar lander by GNC. The focus in the test was to establish the
1/6 g gravity environment on lunar surface. There were different solutions as follows.
1. Helicopter
The idea was to suspend the lunar lander with a cable by helicopter. During the test,
the helicopter lifted the lunar lander to the test height, and then the helicopter was
hovering. After it was ready, the cable would balance part of weight of the lunar
lander by the force sensor and control system on the helicopter, while the engine on
the lunar lander was firing to conduct test.
The disadvantage of this solution was that the hovering stability of the helicopter
could not meet the requirements, and the pilot’s operational response time was much
longer than the GNC control period of the lunar lander. In addition, there was potential
hazard.
2. Balloon
The idea was similar to the helicopter solution, with helium balloon instead of helicopter. The disadvantage of this solution was that the balloon volume would be
greater than 1000 m
3 and the air drag on the lunar lander during descent would be
greater than 4000 N. Therefore, it could not meet the test requirements.
3. Scale Model
The idea was to develop a dynamic scale model of the lunar lander whose mass and
engines were determined by the similar theory to meet the test requirements. The
disadvantages of this solution were: (1) It was difficult to develop a scaled model
according by the similar theory. For example, the thrust of attitude control engine
should be consistent with the scale. (2) The technical status of the scale model was
different from real lunar lander, which made it difficult to verify the real lunar lander.
4. Aero engine
The idea was to use an aero jet engine to balance part of weight of the lunar lander.
In the test, the jet engine was applied to lift the lunar lander up to the test height, and
then the thrust was reduced. At the same time, the engine of the lunar lander was
fired and the test was started. The disadvantages of this solution were: (1) because of
the structure limitation of the lunar lander, it was difficult to install the aero engine
and the throttling engine at the same time, which would result in change of lunar
lander configuration. (2) After the aero engine was installed, it was necessary to be
controlled and cooperate with throttling engine, which would increase the difficulty
of control. (3) There was potential hazard in the test. Once there was accidental
explosion of LLRV happened in the United States.
495
15.4.2 Test Constraints and Methodology
In ground environment, the thrust of throttling engine could not balance weight of the
lunar lander, and it was difficult to satisfy the test requirements for control of velocity
and attitude of the lunar lander by GNC. The focus in the test was to establish the
1/6 g gravity environment on lunar surface. There were different solutions as follows.
1. Helicopter
The idea was to suspend the lunar lander with a cable by helicopter. During the test,
the helicopter lifted the lunar lander to the test height, and then the helicopter was
hovering. After it was ready, the cable would balance part of weight of the lunar
lander by the force sensor and control system on the helicopter, while the engine on
the lunar lander was firing to conduct test.
The disadvantage of this solution was that the hovering stability of the helicopter
could not meet the requirements, and the pilot’s operational response time was much
longer than the GNC control period of the lunar lander. In addition, there was potential
hazard.
2. Balloon
The idea was similar to the helicopter solution, with helium balloon instead of helicopter. The disadvantage of this solution was that the balloon volume would be
greater than 1000 m
3 and the air drag on the lunar lander during descent would be
greater than 4000 N. Therefore, it could not meet the test requirements.
3. Scale Model
The idea was to develop a dynamic scale model of the lunar lander whose mass and
engines were determined by the similar theory to meet the test requirements. The
disadvantages of this solution were: (1) It was difficult to develop a scaled model
according by the similar theory. For example, the thrust of attitude control engine
should be consistent with the scale. (2) The technical status of the scale model was
different from real lunar lander, which made it difficult to verify the real lunar lander.
4. Aero engine
The idea was to use an aero jet engine to balance part of weight of the lunar lander.
In the test, the jet engine was applied to lift the lunar lander up to the test height, and
then the thrust was reduced. At the same time, the engine of the lunar lander was
fired and the test was started. The disadvantages of this solution were: (1) because of
the structure limitation of the lunar lander, it was difficult to install the aero engine
and the throttling engine at the same time, which would result in change of lunar
lander configuration. (2) After the aero engine was installed, it was necessary to be
controlled and cooperate with throttling engine, which would increase the difficulty
of control. (3) There was potential hazard in the test. Once there was accidental
explosion of LLRV happened in the United States.