Science: Meteor Tunnel

Missile and space flight enthusiasts talk calmly about speeds above 10,000 m.p.h. Anyone who thinks that it will be easy to fly at such speeds has only to visit the Cornell Aeronautical Laboratory at Buffalo, N.Y. and watch the tests being run in its hypersonic wind tunnel.

The hypersonic tunnel is a vacuum chamber at one end and a gas-charged cannon at the other. At the beginning of each test, a strong-walled tube six feet long and three inches in diameter is charged at high pressure with an explosive mixture of hydrogen, oxygen and helium. When the gas is detonated (with a bang like a 37 mm. gun), it ruptures a copper diaphragm. A blast of hot gases preceded by a shockwave races down a long evacuated tube. Pushed by pressure behind and pulled by the vacuum ahead, it expands through two nozzles and in a twinkling reaches the speed of 10,000 m.p.h. (13 times the speed of sound).

Standing in its path are miniature models of guided missiles or their components. By the time the wave of gas reaches them, it has expanded so much that its temperature has fallen to that of the stratosphere, about —68° F. But when it hits a model, friction heats the gas to 7,000° F., making it brightly luminous. The gas streams around the model like the glowing trail of a meteor. The flow lasts so short a time (1/1000th of a second) that the model is not damaged, but this brief period is long enough to permit the scientists to study its effects.

Cornell uses the hypersonic tunnel to find out what will happen to a guided missile that enters the atmosphere from space at many times the speed of sound. Even if it flies perfectly straight, it gets a rugged workout, with luminous gas racing around it hot enough to melt or vaporize any known substance. If it enters sideways with a yawing motion, as is more likely, the heating effect is much greater. A steel ball or a sharp-edge wedge turns into an artificial meteor.

Cornell’s tunnel is an experimental model. A much larger one copied from it will be built at the Air Force’s Arnold Engineering Development Center at Tullahoma, Tenn. Details of construction are secret, but the objective is not: to learn to make missiles behave like meteors, yet survive unmelted to complete their missions.