During the Second Wold War, fighter pilots found that their planes became difficult to control when they reached speeds of around 870 kilometers an hour. They were getting close to the speed of sound, know as the 'sound barrier'. Many experts brlieved that no aircraft could ever go that fast and survive. But it didn't take long for someone to prove that those experts were wrong. These days many aircraft can fly faster than the speed of sound. Most of them are military aircraft, but there was one - the Concorde - that carried passengers.
The Concorde was a technological marvel. When Charles Lindbergh flew across the Atlantic Ocean for the first time in 1927, it took him more than thirty hours. A Concorde could make the same journey in under four hours. But it wasn't cheap. In 2002, aseat on a Concorde flight from New York to London cost over US$6,300. But for that, you got to travel at twice the speed of sound, 18,288 meters above the ground. Only astronauts fly higher.