Long-Forgotten Debris May Pose a Fatal Threat
By ANDREW C. REVKIN
The domain of the space shuttle is relatively free of space junk, the flotsam from hundreds of satellite launches, but even so there is plenty to threaten the
orbiters, and much of it escapes detection. So as investigators try to determine how the shuttle Columbia was lost, space debris is a suspect.
Some 84 percent of the known debris — about 8,000 pieces of detritus left from every old satellite or used-up booster rocket launched since Sputnik in 1957 —
lies more than 500 miles up, twice as high as the orbit of the International Space Station, according to officials of the Air Force Space Command, which maps
space debris. That is ordinarily the highest altitude the shuttles reach. On scientific missions like the Columbia's, the orbiter flies about 180 miles high.
NASA and independent experts have always calculated as extremely remote the chances of a shuttle suffering fatal damage in a high-speed collision with orbiting
debris.
But there is plenty of evidence that the shuttles regularly collide with debris. Most shuttle windows carry the pockmarks of collisions with tiny bits of this or that
floating in space.
Also, the Air Force tracks objects only larger than 10 centimeters or so, about the diameter of a softball. There are an additional 130,000 bits and pieces, as small as
a fingernail, that constitute a potent, largely invisible threat mitigated only by the vast empty ocean of space in which they move.
The potency of the threat lies in physics. At the 21,000-miles-per-hour velocities of "low-earth" orbits like those of the shuttles, NASA has calculated that a piece of
aluminum the size of a fingertip — a cubic centimeter — would strike with the kinetic force of a 400-pound safe at 60 miles per hour.
The Air Force estimates that the amount of debris flying around in low-earth orbit is rising by 5 percent a year.
At least eight times, past shuttle missions have had to fire thrusters to avoid charted pieces of debris, said Allard Beutel, a NASA spokesman at the Johnson Space
Center in Houston.
As a result, military and intelligence agencies continued yesterday to sift for any clues of a collision or other event that might lie hidden in masses of data recorded
by spy satellites, mountaintop telescopes that spy on other countries' spy satellites, and a host of other devices pointed at the sky from above and below.
Space agencies in other countries are also looking through their own radar and telescopic records.
"We've been asked by NASA to look at all the data in a certain time frame to determine what possibly could've been seen or been gathered," said Lt. Col. Andy
Roake, a spokesman for the Air Force Space Command at Peterson Air Force Base in Colorado. The data, most from reconnaissance efforts, are being screened
before they are sent on to NASA.
"Data from different radars and cameras and telescopes that different parts of the military have are all being funneled up," Colonel Roake said.
The data are flowing to NASA through the United States Strategic Command at Offutt Air Force Base in Nebraska, he said.
Other agencies, including the National Reconnaissance Office, which manages spy satellites for the Pentagon and the C.I.A., have been consulted, NASA officials
said, although officials at the office declined to comment on the process.
They are seeking hints of either something striking or leaving the craft, space agency officials said.
Of particular interest is Jan. 17, the day after the Columbia settled into its orbit to conduct two weeks of medical and other research, Air Force and NASA officials
said. An analysis of Air Force radar from that date showed something leaving the vicinity of the shuttle and, two days later, burning up in the atmosphere.
That information is being analyzed, and the prospect of a collision in orbit remains one of many possibilities, Mr. Beutel said.
"We're not putting any more or less emphasis on that particular theory as opposed to anything else," Mr. Beutel said. "It's still pretty early in the game. It's just a
couple days ago that we got the Air Force data."
Space experts and NASA officials describe the threat from space debris as extraordinarily remote yet potentially devastating.
Several times in recent years, NASA and the military agencies have carefully swept particular regions in space to see if they can expand the list of known objects,
cutting the chance of a surprise strike on a shuttle or other spacecraft.
William Ailor, the director of the Center for Orbital Reentry and Debris Studies of Aerospace Corp., an Air Force contractor, said commercial satellite launches
were in particular peril because they did not have access to all the data.
Nonetheless, the list of known threats pales beside the list of those that are not, Mr. Ailor and other experts said.
These occasional efforts have confirmed that much more debris is slinging around the planet, but they have not yet resulted in a detailed map showing the orbital
paths of the objects, Mr. Ailor said.
Finally, he and other experts said, even the most advanced technologies cannot discern something the size of a peanut M&M, and yet something that size could
penetrate a spacecraft's shields and insulation and lead to catastrophe.
NYTimes |
