The challenges of steering a hypersonic plane

Mach 5 is the new Mach 1. 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. While re-entering spacecraft and intercontinental ballistic missiles have rushed through the atmosphere at this speed for decades, they are not very steerable. The dream is of vehicles that can be manoeuvred in a manner more like conventional aircraft. At first, these machines would be military missiles. But some dreamers suggest hypersonic passenger flight might eventually be possible.

Steering hypersonically using conventional control surfaces, like wings and ailerons, is out of the question. The forces and heat involved would destroy them. Smaller versions called trim tabs can help a bit. But what is really needed is a different approach. And, as he told delegates at last week’s meeting of the American Association for the Advancement of Science in Denver, Hisham Ali of the University of Colorado, Boulder, is one of those proposing just that. He thinks the answer is to be found in a field called magnetohydrodynamics.