Late last month GOES-13, a weather satellite that helps the U.S. government forecast hurricanes, got smacked by a piece of supersonic space dust. A little micrometeorite, a small-but-incredibly-fast piece of space debris, says USA Today, “struck the arm of the satellite’s power-producing solar array, engineers say. The jolt knocked the satellite off balance, and spacecraft instruments automatically turned themselves off.” The orbital collision brought the satellite down for a few weeks as engineers figured out what was wrong.
Astronauts on the International Space Station have had their own run-ins with micrometeorites, too. Last year, one slammed into one of the station’s giant windows. “Micrometeroid and orbital debris (MMOD) impacts are part of life in low Earth orbit,” says Space Safety Magazine. “MMOD impacts occur all the time on ISS and other spacecraft, although most are not easily visible through a window. Returning Space Shuttles have shown pock marks from high velocity MMODs.” As humans enter low-Earth orbit with increasing regularity, the threat posed by small bits of space debris—an errant bolt, say—goes up.
To protect satellites and astronauts (and soon, space tourists), engineers have to give the ships some sort of armor. Right now, NASA uses something called “Whipple Shielding”:
In the 1940s, Fred Whipple proposed a meteoroid shield for spacecraft, called the Whipple shield in recognition of his contribution. The Whipple shield consists of a thin, aluminum “sacrificial” wall mounted at a distance from a rear wall. The function of the first sheet or “BUMPER” is to break up the projectile into a cloud of material containing both projectile and BUMPER debris. This cloud expands while moving across the standoff, resulting in the impactor momentum being distributed over a wide area of the rear wall (Figure 2). The back sheet must be thick enough to withstand the blast loading from the debris cloud and any solid fragments that remain.
In updated versions of this design, says NASA, “bulletproof” Kevlar or other materials are placed between the outer sacrificial wall and the inside plate.
The designs amount to, essentially, putting something thick in the way that will hopefully stop the micrometeorite before it can ram its way all the way through your spacecraft. But once that hole is punctured, the strength of the shield is reduced until it can be repaired—not the greatest if you want to leave your satellite up there for years at a time, or you want your commerical space ship to do back-to-back flights.
The future of spacecraft shielding could stem from ongoing research into “self-healing” shields, materials that automatically repair themselves after they’re hit. The CBC recently toured the Planetary and Space Science Centre at the University of New Brunswick, where researchers use a gigantic gun to simulate micrometeorite strikes and test the space shields of the future.
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