宇航员们今天将做最后一次尝试，把一颗通讯卫星从它无用的轨道上拯救出来。
Astronauts will make a final attempt today to rescue a communications satellite from its useless orbit.
有一次，我们看到它以与轨道一致的方式移动。
Once, we saw it was moving in a pattern consistent with an orbit.
它们并非经常发生，大约只有一年一次，因为太阳，月亮的轨道相互倾斜，它们很少能排成一条直线。
They don't happen often-only about once a year-since the tilted orbits of the sun, moon, and Earth make their alignment rare.
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