Fastest Gun on Earth: Goals Go Beyond Planet
By MALCOLM W. BROWNE
Published: March 22, 1994
USING an experimental gun about 60 feet long, scientists at Sandia National Laboratories have blasted a small projectile to a speed of 10 miles a second, which is thought to be the highest velocity ever reached on earth by any object larger than a speck of dust.
In announcing the achievement, Sandia said its new gun, the Enhanced Hyper Velocity Launcher, would enable engineers to measure the effects of a micrometeorite or chunk of space debris colliding head on with an orbiting space station at a combined speed of 36,000 miles an hour. The gun will also help engineers to design and test protective shields for orbiting communications satellites.
In an earthbound application, projectiles fired by the gun will be used to study the transitions that gases and other materials undergo when subjected to immense pressures, pressures normally found only in the cores of giant planets like Jupiter.
To break the projectile speed record, Dr. Lalit C. Chhabildas (pronounced cha-BILL-dahs) and his colleagues at Sandia, in Albuquerque, N.M., invented a modification that greatly increased the muzzle velocity of projectiles fired from an existing laboratory gun, which had previously achieved a record velocity of nine miles a second, or 32,400 miles an hour. Leaving Bullets Behind
The record speed, established this month, measured by flash X-rays and other devices, is approximately 27 times as great as that of a bullet fired from a high-powered rifle.
Dr. Chhabildas said in an interview that microscopic dust particles had been accelerated electromagnetically to close to 30 miles a second (108,000 miles an hour), but that the Sandia gun was the first to accelerate projectiles weighing up to one gram (0.035 ounces) to such "hypervelocities."
Gas guns used by laboratories that study high-velocity projectiles generally have two stages. At Sandia, a federally financed national laboratory that develops nuclear and conventional weapons systems, the research gas gun has two barrels placed end to end, about 60 feet in total length.
In the first barrel, 3.5 inches in diameter, a charge of burning powder drives a heavy plastic piston down the bore, compressing hydrogen gas in the chamber ahead of it. When the hydrogen reaches a pressure about 10,000 times that of the atmosphere, a barrier disk ruptures and the hydrogen blasts into the second barrel, one inch in diameter, to drive another piston.
This second piston, Sandia's new invention for achieving cosmic velocities, is called a "pillow," because it is designed to soften the shock it applies to a target at impact. The pillow, or "graded density impactor," which is made of many layers of compressible and resilient plastic, is hurled through a short section of vacuum tubing, after which it hits the projectile, a small titanium disk called a flier plate.
When the pillow hits the projectile, it drives the flier plate forward at nearly its own impact velocity. But then the resilient material in the pillow, having absorbed the energy of the shock, recoils and converts its stored energy to accelerate the projectile still further. Avoids Vaporization
Without the pillow, Dr. Chhabildas said, the gun was capable of accelerating projectiles to 7.6 miles a second. Moreover, the violent shock of an ordinary piston striking a flier plate was sufficient to vaporize it, leaving nothing solid to serve as a projectile.
Now that the pillow has proved successful, he said, it may be possible to accelerate projectiles to 11 miles a second (39,600 m.p.h) or more.
At such high velocities, impacts might be capable of compressing and heating hydrogen sufficiently to initiate fusion, he said, although such an approach to harnessing fusion energy is purely speculative at this point.
Meanwhile, another nuclear weapons laboratory, Lawrence Livermore Laboratory, in Livermore, Calif., is trying to perfect another type of high-velocity gun -- one that could fire heavy payloads into orbit without the use of an expensive rocket.
Livermore's Super High Altitude Research Project gun cannot achieve the enormous velocities of the Sandia gun, but it has been used in recent months to accelerate prototype engines to speeds up to 9,000 miles an hour, speeds such "scramjet" engines must reach before they can operate. Scramjets, which would have features of both jet engines and rocketlike ram jets, are being developed as power plants for future supersonic airplanes.
Eventually, Livermore scientists hope, their gas gun might be used to fire into orbit large projectiles containing building materials for a space station. Material that could stand the shock of launching by cannon could be delivered to orbit much more cheaply by gun than it could as freight aboard the space shuttle.