Courtesy Lawrence Murr, University of Texas at El Paso.
Courtesy Lawrence Murr, University of Texas at El Paso.
This small crater on an aluminum plate was made by a glass pellet moving 4 kilometers per second. The pellet disintegrated.
This deeper crater was made by a tungsten carbide pellet moving 2 kilometers per second. A slower, denser pellet caused much deeper penetration than a less dense, but faster, pellet.
Faster than a speeding bullet
Eight kilometers per second -- the speed often cited for space collisions -- is indeed faster than a 9 millimeter round, which travels at 0.9 kilometers per second. Although eight kilometers per second sounds intimidating, lots of particles strikes satellites more slowly -- and cause much more harm, even if they're the same size.
Lawrence Murr of the University of Texas, who investigates the issue, says, "One kilometer per second has a totally different effect than five kilometers per second." Why? When a tiny particle strikes the multilayer shielding on a spacecraft at, say, 8 kilometers per second, it shatters almost instantly, making smaller particles that whack the next layer of foil, shattering further. By the time the remains hit the third layer, Murr says, they've pretty well spent their momentum -- and don't penetrate.
(Remember, penetration's a problem if you're depending on a spacecraft wall to contain air so you can breathe.)
But with slower particles, shattering doesn't occur, so the damage becomes much greater. "It makes a terrific effect," Murr says. "It's really a pretty staggering phenomenon."
When it comes to being bombarded by space junk, size matters. Denser particles are more dangerous. Velocity also matters, but not in the straight-line way you might think. In other words, faster may be less perilous than slower.
The Gardol shield
Here's a comforting thought: Russia is building shielding for the international space station, but it's overdue, and the first astronauts won't benefit from it for a couple of years (see "Space Station Faces..." in the bibliography).
Without some extreme measures, there's the chance that our very success in orbit will cause us to lose the incredible benefits of spaceflight. That's something to discuss next time you're yakking on a cell phone, which may be transmitted by satellite.
Want to put the skunk on space junk?
Shielding against those dense particles requires lots of mass, Murr says, but launching massive stuff into space is expensive. Even if several inches of aluminum were used, Murr says, "Things would go through that if they're going slow."
