A novel time-optimal trajectory planning approach for underactuated spacecraft is presented by using differential flatness in this paper.For given initial and final states,a performance index is used to minimize the maneuvering time subject to control input saturation constraints.An asymmetric underactuated spacecraft is non-flat unless a fictitious control variable is employed along the uncontrolled axis.Then,the attitudes and inputs can be parameterized in terms of a set of fiat outputs and their derivatives.However,in order to ensure the equivalence,an additional constraint to maintain the fictitious input zero must exist.Further,discretizing the flat outputs by pseudospectral method,the optimization problem is ultimately converted into a lower-dimensional nonlinear programming problem,which contains only algebraic constraints and can be solved numerically without integrating differential dynamics equations.Simulation results demonstrate that this proposed approach is effective in decreasing required solution time and provides comparable computational accuracy.%针对非轴对称欠驱动航天器提出了一种新的基于微分平滑特性的时间最优轨迹规划算法.首先,在控制输入受限的约束条件下,对给定的初末姿态,选取航天器机动时间最短为待优化的性能指标.其次,在欠驱动航天器的非受控轴上引入虚拟控制输入,扩展系统的平滑特性,从而使得系统的姿态和控制输入变量均可由平滑输出函数及其各阶导数代数表征；同时为保证优化问题的等价性,引入虚拟控制输入始终为零的附加等式约束.进一步,利用伪谱法离散系统的平滑输出函数,将优化问题最终转化为一个低维的,仅含有代数约束的非线性规划问题,且无需积分求解系统的动态力学方程.仿真结果表明该算法不仅能够有效地减少优化所需的时间,而且运算精度较高.
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