When a space probe leaves Earth's atmosphere, it must overcome the force of gravity, which exerts a pull on any object near the Earth's surface. As the probe gains speed, the force of gravity decreases, eventually reaching a point where it becomes negligible compared to the propulsive force generated by the probe's engines. Beyond this point, the probe can travel freely through space, unaffected by Earth's gravitational pull. At what point the probe leaves Earth's atmosphere depend on a number of factors, including the size, shape, weight , thrust of the probe.

However, the boundary commonly use to mark the edge of Earth's atmosphere , the Karman line , is set at an altitude of 100km.