航天器(spacecraft)

设计在地球低层大气上按受控飞行路线运行的载人或不载人的飞行器。由於这种环境的高度真空，流线型并不需要，航天器的外观便根据它的任务来设计（参阅space exploration）。多数航天器不是自我驱动的，通常依靠两级火箭来加速到必要的高速度，而两级火箭在油料用光後便投弃掉。一个主要的例外是太空梭轨道飞行器，它使用三个随之携带的液体燃料的重要引擎到达宇宙，而这又是由一个可任意使用的外部箱和一对固体燃料後援器来供给的。航天器进入围绕地球的轨道，如果给予足够的速度，它会继续朝着太空的另一个目的地前进。该机器可以有它自己的小型火箭发动机来定位和发动。至於内在动力，绕地球环绕的航天器使用太阳电池和存储电池、燃料电池，或是两者的结合，而深太空探测器经常使用靠放射性元素加热的热电发生器。设计的高度复杂性，尤其是有人驾驶的有数百万元件构成的航天器，要求高度的小型化和可靠性。

English version：

spacecraft

Vehicle designed to operate, with or without a crew, in a controlled flight pattern above earth's lower atmosphere. Since streamlining is not needed in the high vacuum of this environment, a spacecraft's shape is designed according to its mission (see space exploration). Most spacecraft are not self-propelled; they are accelerated to the necessary high velocity by staged rockets, which are jettisoned when their fuel is used up. A major exception, the space shuttle orbiter, uses three onboard liquid-fuel main engines supplied by a disposable external tank and a pair of solid-fuel boosters to reach space. The spacecraft goes into an orbit around earth or, if given enough velocity, it continues toward another destination in space. The craft may have its own small rocket engines for orienting and maneuvering. For internal power, earth-orbiting spacecraft use solar cells and storage batteries, fuel cells, or a combination, whereas craft designed for deep-space missions usually carry thermoelectric generators heated by a radioactive element. The enormous complexity of design, particularly of manned spacecraft with their millions of components, requires a high degree of miniaturization and reliability.