July 02, 2013
Researchers are using supercomputers at the Texas Advanced Computing Center (TACC) to simulate high-speed collisions with the hope of figuring out ways to make better shields--for spacecraft and for people.
Most of the stuff floating in Earth's orbit is relatively small. But because it moves very fast--up to 15 kilometers per second--it poses a significant threat to manned spacecraft and unmanned satellites. Since there is no feasible way to clean up all the space junk, scientists are looking for ways to make stronger shields for spacecraft and satellites.
The problem is, predicting how orbital debris will affect a spacecraft upon impact is a difficult task. For starters, there's not a lot of experimental data to base assumptions on. NASA scientists have a gas gun that can accelerate small pieces (1 centimeter) of material to speeds of 10 kilometers per second. But with 21,000 pieces of baseball-size debris (larger than 10 centimeters) floating about--and some speeding along at 15 kilometers per second--the physics are beyond what can be reproduced on earth.
Also, because of the speeds of orbital impacts, they're classified as "shock"-type impacts that generate a significant amount of heat that must be accounted for.
That's when researchers turned to supercomputers to provide an answer. Eric Fahrenthold, professor of mechanical engineering at The University of Texas at Austin, leads a team that developed an algorithm that can simulate the shock physics of orbital debris hitting a spacecraft.
Fahrenthold and his team ran the algorithm hundreds of times on three of TACC supercomputers--Ranger, Lonestar, and Stampede--to generate a series of "ballistic limit" curves. These curves tell NASA whether the layers of Kevlar, metal, and fiberglass that makes up a spacecraft's shield can successfully defend a certain size projectile moving at a given speed and angle. The ballistic curves are then validated using real-world gas-gun data to insure that they accurately capture the dynamics of hypervelocity impacts.
"We validate our method in the velocity regime where experiments can be performed, then we run simulations at higher velocities, to estimate what we think will happen at higher velocities," Fahrenthold explained in a recent story at the TACC website. "There are certain things you can do in simulation and certain things you can do in experiment. When they work together, that's a big advantage for the design engineer."
Fahrenthold and his team are using the same algorithms and models to simulate the impacts of bullets on body armor, too. This work, which is funded by the Office of Naval Research, has similarities to the spacecraft shield study, since both utilize Kevlar. However, according to Fahrenthold, nobody has taken this hybrid-type approach to studying body armor.
According to TACC, Fahrenthold's models take into account variables such as the material's strength, flexibility, and thermal properties, and can accurately capture the complex interaction of the multiple layers of a fabric protection system.
"Using a hybrid technique for fabric modeling works well," Fahrenthold said. "When the fabric barrier is hit at very high velocities, as in spacecraft shielding, it's a shock-type impact and the thermal properties are important as well as the mechanical ones."
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