我们将此弹道问题转化成最优控制问题，通过极大值原理得到最优弹道的一阶必要条件。

The trajectory problem was cast as the optimal control problem and Pontriaghin Maximum Principle was used to obtain first order necessary condition.

youdao

This was a first order condition or a first order necessary condition.

这个只是一阶条件,是必要条件

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