NASA should do more to prevent potentially catastrophic collisions between the space shuttle and orbiting chunks of space junk, says a report released today by the National Research Council (NRC). The NRC's expert panel concluded that Earth's thickening layer of drifting debris--especially small metal fragments and paint chips--almost doubles the accident risk faced by some shuttle crews.
When engineers designed the space agency's four shuttles in the 1970s, debris wasn't considered a significant threat to the lightly-armored craft. But radar surveys have shown that space is getting crowded. Forty years of space exploration have added millions of pieces of junk, from abandoned satellites to nuts and bolts, to the planet's natural blanket of orbiting meteoroids and dust. Traveling at 7.5 kilometers per second (17,000 miles per hour), the debris can vaporize metal and cause destructive hypervelocity shock waves during collisions. A 0.5-centimeter fragment, for instance, could punch a fist-sized hole in the shuttle's crew compartment or wing. Although radar systems on the ground can detect large piece of debris and help astronauts avoid them, more than 95% of flotsam is too small for the sensors to track.
The NRC panel recommended that NASA look for ways to reduce the odds of a catastrophic collision during a shuttle flight to less than 1 in 200. The agency may need to revamp the computer models it uses to calculate how much damage small fragments can cause, beef up the debris surveillance network, alter flight rules that limit the shuttle's freedom to maneuver, and add extra shielding to the most vulnerable parts of the shuttle.
"The hazard from meteoroids and orbital debris is, on some missions, the single greatest threat to the shuttle and the crew," says former astronaut and panel chair Frederick Hauck, of AXA Space in Bethesda, Maryland. In fact, he says, the panel judged the danger to be "slightly larger than the hazard from ascent."