月球软着陆的二次型最优制导方法

A Linear Quadratic Optimal Guidance Method for Lunar Soft Landing

为实现在月球表面指定区域的精确软着陆,研究了月球软着陆的线性二次型最优制导方法。利用简化的轨道动力学模型,给出了一种基于状态和能耗最优的软着陆二次型制导方法。由于制导律要求同时提供3个方向的时变推力,所以需要通过变推力发动机和姿态机动来实现。该制导方法虽能满足精确软着陆的需要,但对姿态变化的要求超出了着陆器姿态机动能力。因此,本文修正了二次型最优制导方法,取消了对轨道参数的过程约束,仅对其终端进行约束,通过求解着陆指定目标点的能耗最优两点边值问题,得到了发动机推力大小和方向的显式表达式。研究结果表明,利用一定的姿态机动能力,修正的制导方法能够满足精确软着陆的需要。

To achieve the soft landing on a specified region of lunar surface, the paper studies a linear quadratic optimal guidance method for lunar soft landing. Using the simplified orbit dynamics model, the quadratic guidance method based on optimal states and fuel is presented. It is necessary for this guidance method to provide the time-varying thrust for three directions through a throttleable engine and attitude maneuvers. The guidance method can meet the need of pinpoint soft landing, but its requirement for attitude change goes beyond the attitude maneuver capability of landing spacecraft. So the paper modifies the linear quadratic guidance method. The modified guidance law cancels the process constraint for orbit parameters and only restricts the terminal orbit parameters. The guidance law solves the optimal fuel two point boundary value problem for landing at a specified point, and obtains the explicit expression of magnitude and direction of engine thrust. The research results show that the modified guidance law can meet the need of pinpoint soft landing using the achievable attitude maneuver capability.