Giant gun fires simulated space junk
Engineers at the University of Dayton Research Institute are wrenching, bolting and pumping, preparing to fire the world's only three-stage light-gas gun. They're about shoot an aluminum BB at more than 5 miles per second. At that rate it could travel from Dayton to Columbus in just 15 seconds-- but this BB will go only nine feet before it hits its target and shatters.
These fast-flying aluminum balls simulate space junk orbiting the earth. The targets are materials that could be used to armor spacecraft. If the materials survive impact with a high speed aluminum ball, chances are they would also survive collisions in space. Kevin Poormon, senior resesarch engineer at the UDRI, says that man-made space junk poses a serious threat to space craft.
"Every time we launch something up there we put a little more junk up there," he said. "It is a serious problem and it is the most threatening thing that can happen to a shuttle or a space station as far as hazards that they face in space."
NASA tracks the largest pieces of debris, but even the ones too small and too numerous to track can rip through spacecraft armor. This is what Poorman and impact physics engineer Andy Piekutowski want to avoid. They use powerful guns to test materials in the lab before they go into orbit.
The average speed of a collision between a spacecraft and damaging debris is at least 20 thousand miles per hour. To imitate this debris, the aluminum spheres have to reach this speed, and they have to do it without melting or disintegrating before they hit the target.
Until recently, there was no gun in the world that could accomplish this feat. But Piekutowski and Poormon revived and refined a technology from the 1960's, turning an abandoned idea into record-breaking achievement.
"That's the big success we've had over the last six months or so," Poormon said. "We've been able to launch the projectile without having to replace anything. Everything comes apart real nicely, we're not having to replace the gun barrel or the high pressure section or anything like that."
Their masterpiece is known as a three stage light gas gun, named for the three distinct chambers of hydrogen gas that build up its power.
The first of the three chambers is filled with compressed hydrogen and loaded with more than a pound of gun powder. When the gunpowder ignites, it drives a piston down the chamber, compressing the hydrogen until it bursts through a metal plate into the second, narrower chamber.
In the second chamber, the gas launches a smaller piston so fast it causes a shock wave that fires the aluminum sphere out the third and final chamber toward the target. The gas pressure in the chambers can top 130 thousand pounds per square inch.
Once fired, the pellet passes through a series of laser beams that allow the researchers to calculate its speed. They also x-ray it to record how it holds its shape and then deforms or shatters when it hits the target.
"Our claim is that we're shooting a controlled shape," Poormon said. "If you want a sphere we can shoot a sphere. If you want a disk we can shoot a disk. And then you would know it's not a molten piece of material, it's essentially cold material going down there with known properties."
But Piekutowski and Poorman are still fine tuning their gun before they take aim at spacecraft armor. They want to adjust the amount of gun powder and the pressure of hydrogen for an optimum firing. They're also testing a new way of separating the aluminum sphere from its sabot-- the carrier that makes it fit the gun barrel.
It takes about two and a half hours to prepare the gun, but it's almost ready to fire for the newest test. Piekutowski crouches inside the blast chamber, setting up the target and the x-ray system. When he comes out, he bolts on the airtight door. They pump the air from the blast chamber and the gun chambers. In the gun, they replace the air with hydrogen gas. Finally Piekutowski screws on the gunpowder charge. Everyone retreats to the control room, the doors to the firing range lock shut and an alarm sounds before the gun fires.
Piekutowski and Poormon are pleased with the day's results. The sphere passed through the laser beams intact. It separated from its sabot, or carrier shoe, before it hit the target. And it reached a speed of over 20 thousand miles per hour, as planned. It hit the target a little high, and once they look at the x-rays they'll know more about what to adjust in their next test.
Because of the hours of prep time, cleanup and analysis, they can only shoot the gun once per day. But each firing brings them closer to helping spacecraft and their crews survive collisions with orbiting garbage.