星下点轨迹周期性出现重叠现象，即经过一定时间后，星下点轨迹又重新回到原来通过的路线，此类轨道称为回归轨道，或称为重访轨道、循环轨道。重叠出现的周期称为回归周期。
而回归轨道的特点是周期性地覆盖地球，这有利于对地球上动态目标的侦察。
And the regressive orbit satellitr's trait is that the satellite can cover the earth periodic, it benefits the dynamic reconnaissance.
阐述了临界倾角太阳同步回归轨道这种特殊椭圆轨道的设计方法，总结了其轨道要素的计算步骤。
The method of designing special elliptic orbit which was critical inclined, sun synchronous and repeating ground trace was expounded, and the calculation process of this method was summarized.
太阳同步回归轨道既可以满足光照条件的要求，又可以满足时间分辨力的要求，是对地观测航天器首选轨道之一。
Repeat sun-synchronous orbit is one of the most important orbits for earth observation missions, because the orbit can satisfy the requirements of illumination and temporal resolution.
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