宇宙飞船需要火箭产生的巨大动力才能发射进入太空。火箭在工作时会燃烧能源,排出气体产生强大的推动力,从而使飞船达到所需要的高度和速度。达到这种效果最有效的途径是把火箭分成几级,一般是三级,一层一层依次堆叠在一起。第一级火箭搭载着飞船到达高空大气层。一旦燃料耗尽,已经空了的一级就会落回地球。更轻一些的第二级会在脱落前把飞船带向更高的速度。最后一级则把宇宙飞船推入轨道,或是太空中更远的地方。 Spacecraft need a huge rocket engine to launch into space. The rocket burns energy at work, leaving a strong impetus to the exhaust gas to achieve the required altitude and speed. The most effective way to achieve this effect is to divide the rocket into several levels, usually three levels, one after another in layers. The first stage rocket carrying the spacecraft to reach the upper atmosphere. Once the fuel is exhausted, the level that has been empty will fall back to Earth. The lighter second stage will take the spacecraft to a higher speed before it falls off. The final stage put the spacecraft into orbit, or farther in space.