They float freely in three dimensions But as that space shuttle returns to Earth, and as the astronauts enter the Earth's gravitational field, they begin to see the effects of gravity.
他们不受重力影响 在三维空间里自由漂浮 但是一旦航天飞机 回到地球 宇航员就进入地球的引力场 他们就开始受重力影响了