基于改进凸优化方法的火箭着陆段制导研究

Research on rocket landing phase guidance based on improved convex optimization method

火箭垂直着陆理想状态是下降过程中保持推力值接近重力大小,着陆瞬间等于重力。目前使用广泛的凸优化制导方法产生的推力调节曲线为Bang-Bang形式,发动机根据当前状态和目标状态调节推力在最大值与最小值之间跳变。采用凸优化方法制导使得火箭下降过程中加速度过大,其稳定性无法保证。提出了一种基于改进凸优化方法的火箭着陆制导律。以燃料最优为目标,使用基于凸优化的制导方法规划产生初始轨迹。在初始规划控制曲线上选取合适离散点,计算基于凸优化制导律控制量相邻两离散点之间的斜率值,将计算所得斜率突增点作为算法切换点,在火箭调节推力值到达突增点时切换为基于四次多项式的制导律直至着陆。仿真结果表明,相比于现有的单一制导方法,所提出方法解决了传统凸优化方法应用过程中减速过快的问题,同时最大程度上减少了燃料的消耗。

The ideal state for rocket vertical landing is to maintain thrust close to the gravitational force during the descent and equal to the gravitational force at the moment of landing.Currently,the widely used convex optimization guidance method generates a thrust adjustment curve in the form of Bang-Bang,where the engine adjusts the thrust between maximum and minimum values according to the current and target states.The use of convex optimization guidance results in excessive acceleration during the rocket’s descent,and its stability cannot be guaranteed.Therefore,this paper proposes an improved convex optimization-based rocket landing guidance law.With fuel optimization as the goal,a trajectory planning method based on convex optimization guidance is used to generate the initial trajectory.Suitable discrete points are selected on the initial planned control curve,and the slope value of the control quantity based on convex optimization guidance between two adjacent discrete points is calculated.The calculated point of sudden increase in slope is taken as the algorithm switching point,and the guidance law based on the fourth-order polynomial is switched when the rocket adjusts the thrust value to reach the point of sudden increase until landing.Simulation results show that compared with the existing single guidance method,the proposed method solves the problem of excessive deceleration in the traditional convex optimization method and minimizes fuel consumption to the greatest extent.