在轨道上运行的卫星总是要飞离地球，而结果总是被地心引力拉回来。
The satellite traveling in the orbit is always escaping from the earth only to be pulled back by gravity.
然而同时也是地心引力将世界凝聚，使各大行星在轨道上运转，让我们的宇宙井然有序。
But it is also gravity pull that keeps our world together, that keeps the planets in their orbits and our universe in order.
被称为地心引力牵引器将能处于一个离具有威胁的小行星附近，施加一个小的拉力，长时间下去，就可以让小行星拉离轨道。
The so-called Gravity Tractor could maintain a position near the threatening asteroid, exerting a gentle tug that, over time, would deflect the asteroid.
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