Electric propulsion is capable of providing control accelerations of 1 mm/s~2 or less, four or more decimal orders below orbital gravity accelerations. This implies very long inter-orbital maneuvers counting many hundreds of revolutions. Any straightforward numerical method of thrust optimization, quite successful in deep space trajectory design, is doomed to fail when applied to trajectories this long. A practical approach is use of thrust-to-gravity ratio as a small parameter. When dealing with quadratic Quality criteria such as fuel consumption, this approach leads to splitting the problem into a sequence of Two Optimal Control problems, corresponding to "fast" and "slow" time. The strategy has much in Common with the averaging methods widely used in Celestial Mechanics.
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机译：电推进能够提供1 mm / s〜2或更小的控制加速度，比轨道重力加速度低四个或更多十进制。这意味着非常长的轨道间机动计算了数百转。在深空弹道设计中非常成功的任何简单的推力优化数值方法，当应用于如此长的弹道时注定会失败。一种实用的方法是使用推力/重力比作为较小的参数。当处理二次质量标准（例如燃料消耗）时，此方法导致将问题分为两个最优控制问题，分别是“快速”和“慢速”时间。该策略与“天体力学”中广泛使用的平均方法有很多共同点。
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