Imagine, high above you, the sleek silhouette of an airplane with a shape more like that of some futuristic spacecraft from a Hollywood blockbuster. You can clearly make out the long, lance-like nose, steeply swept wing and powerful engines as they blast this 21st-century private jet through the stratosphere at twice the speed of Concorde. Inside, well-heeled passengers are whisked in supreme, supersonic comfort toward their destination half a world away. Rather than a bone-rattling sonic boom, the sound you hear is a mere burble as the jet streaks overhead, vanishing beyond the horizon as quickly as it appeared.
The idea sounds like pure fantasy — and yet this is precisely the dream of a handful of bright entrepreneurs, and even many scientists and engineers at NASA and companies such as Boeing and Lockheed Martin, who say a quiet supersonic transport capable of flying from New York to Paris in less than two hours might be closer to reality than any of us could have imagined.
If such an incredible airplane could be brought to market, it would represent the ultimate in luxury travel — and a potentially potent business tool, too. After all, at its essence a private jet is really little more than a time machine, albeit one with a comfortable interior and a wet bar. And a supersonic private jet would be the ideal such conveyance, allowing its owner to move from point A to point B in the minimum amount of time.
When it comes to future supersonic jet design, there are two schools of thought. The first holds that a civil supersonic transport should be able to fly much faster than the speed of sound over the ocean and the uninhabited parts of the earth, then slow down to high-subsonic speed for the portions of its journey over populated regions. The second school — and the one that is quickly winning the upper hand in the debate — says that for supersonic travel to make economic sense, such an airplane should be capable of flying at speeds well above Mach 1 during its entire time aloft, other than takeoff and landing.
Anatomy of a Sonic Boom
Before we discuss the ways in which researchers hope to quiet the noise caused by sonic booms, let’s tackle the question of what happens when an airplane breaks the sound barrier.
When an object passes through the air, it creates a pressure wave ahead of it and behind it — similar to the bow and stern waves of a boat. As the speed of the object increases, these waves travel at the speed of sound and are increasingly forced together, or compressed. Because the waves can’t get out of the way of each other, they eventually merge into a single shock wave at the speed of sound — the critical speed known as Mach 1, measured as approximately 667 knots at sea level and a temperature of 20 degrees C (68 degrees F).