Realization Chang'e-3's Main deceleration stage and Rapid adjustment stage just based on differentiation and search

This paper first proposed some reasonable assumption, it simplified controlling problem for Chang'e-3's main deceleration stage and rapid adjustment stage. Thus put forward these two stages' plane model that basing on the second derivative. But it is not easy to be solved. Then the method of two simple algorithms: differential approximation and search is proposed to achieve more accurate calculation, and the computational problem of the model is solved. In the main deceleration stage takes strategy that the thrust is fixed at 7500N, and searching for good thrust direction angle of the reverse speed. And a good result has been searched: the angle is 6.63°, last current state resultant velocity is 56.7m/s and the height is 3001.84m, take 414s and fuel consumption is 1055.7Kg. And in the rapid adjustment stage takes strategy that the thrust is fixed just reverse velocity, and searching for good thrust size to meet the control requirements, then a good result has been searched: reverse thrust size is 4050N, the end of the state as horizontal velocity is 0.04m/s and the height is 3001.84m, the running time is 25.8s and fuel consumption is 35.54Kg. These results are more satisfactory than the existing literature. Finally, the advantages and disadvantages of the model are analyzed. It is found that the algorithm is simple and the control strategies are simple too.