If something's traveling supersonically, you can see it coming, but you won't hear it at all until it's already passed you.

如果有东西以超音速飞行，你可以看到它过来了，但在它真正经过你身边之前，你根本听不到它的声音。

Just as aviators of old sought to break the sound barrier and travel supersonically, the search is now on for reliable and controllable ways to travel " hypersonically" , generally defined as more than five times the speed of sound.

正如古代飞行员力图突破音障， 进行超音速飞行一样，现在人们也在寻找可靠、可控的“高超音速” 飞行方式，高超音速通常被定义为音速的五倍以上。