垂直起降运载火箭返回着陆轨迹在线优化研究

Online trajectory optimization for descent and landing of vertical takeoff and landing launch rocket

针对垂直起降运载火箭返回着陆轨迹优化问题开展了研究。首先,基于多区间Radau伪谱法和稀疏非线性规划技术,采用C++语言编程开发了具有在线优化能力的轨迹优化程序。然后,针对火箭返回着陆轨迹的落点误差较大问题,提出了末段轨迹在线更新的应用模式,以消除轨迹累积误差。最后,开展了仿真计算。研究结果表明:所提方法能够快速求解运载火箭返回着陆轨迹优化问题,计算效率比GPOPS-Ⅱ软件提高大约3~12倍,并且可以移植到嵌入式系统,具有在线优化的能力;对末段轨迹进行在线更新能够有效提高返回轨迹的落点精度。

The optimization of descent and landing trajectory of vertical takeoff and landing launch rocket was studied. Firstly, a trajectory optimization method and program with online capability was developed using C++ language based on multi-interval Radau pseudospectral method and sparse nonlinear programming(NLP). Then, an application mode of online update of the terminal trajectory was proposed to eliminate the cumulative trajectory error. Finally, a numerical simulation was performed. The results show that the proposed method can quickly generate a fuel-optimal descent and landing trajectory for a launch rocket, and the computational efficiency is about 3~12 times higher than that of the GPOPS-Ⅱ software. The method can be easily ported to embedded systems and thus has the potential of online optimization. The online optimization of the terminal trajectory can significantly improve the rocket landing accuracy.