Trash in Space Has Scientists Concerned : Astronomy: Like earthly polluters, spacefarers are feeling growing pressure to clean up their act.
When engineers and scientists discuss the vacuum of space these days, they may be yearning for a giant Hoover.
Like other frontiers before it, the heavenly void has succumbed to human litter. Ground trackers report roughly 7,500 spent rocket stages, dead satellites, screwdrivers and other man-made objects whirling around the globe, passing each other at about 22,000 m.p.h. in relative velocity, at varying altitudes and in all directions. Most of the items are classified as junk.
But that’s only the big stuff--at least 10 centimeters or about four inches across--visible to the ground-based telescopes and radars of the U.S. Space Surveillance Network.
What is giving fits to the orbital garbage gurus are the uncounted trillions of flecks, flakes and fragments of tiny trash too small to be tracked but traveling so fast that if a piece of aluminum one centimeter across (smaller than a marble) collided with a spacecraft, it would have the force--but not necessarily the effect--of a 400-pound safe traveling 60 m.p.h.
Concern about global ring around the collar has increased steadily in the last decade.
In May, the U.S. Space Command’s Space Surveillance Network catalogued the 20,000th man-made object to be launched into Earth orbit since Sputnik went up in 1957.
Most are no longer up there. Over time, orbiting items lose energy and fall into progressively lower orbits until they hit thicker atmosphere, slow down and burn up or, in rare cases, hit the ground.
The greater bulk of the visible junk still aloft is in 3,000 large objects, mostly spent rocket stages and dead satellites, according to government analysts.
Then there are about 4,000 smaller but still trackable fragments, most of which resulted from about 130 “fragmentations”--intentional or accidental explosions or breakups--in orbit.
Some of the debris got there through astronaut mishaps. In 1984, for example, a shuttle astronaut working outside his craft let go of 10 or 12 screws. A space-walking Soviet cosmonaut once dropped a screwdriver. A thermal glove floated out of Gemini 4 in 1965. And there is a nice camera adrift somewhere in space.
In the infancy of the Space Age, it was the harsh natural environment of space--the whizzing meteorites and cosmic radiation--against which engineers armored their craft. Now the estimated mass of man-made stuff orbiting within 1,200 miles of Earth’s surface is 15,000 times the mass of all the natural objects passing near Earth at a given time.
The debris shell has prompted National Aeronautics and Space Administration engineers to add at least five tons of costly shielding to the design of the proposed space station, and they are studying more exotic measures, such as collision-avoidance maneuvering. Space shuttles have collided at least twice with tiny objects.
Space debris is also a problem for astronomers because of light reflecting from orbiting junk.
Experts disagree among themselves over how serious orbital trash is now and how fast the problem will grow. Nobody claims to know for sure. In any case, like earthly polluters, spacefarers are feeling growing pressure to clean up their act, even though the impact, literally, of all the junk on spaceflight has been minimal--so far.
In 1980, scientists at Johnson Space Center examined surfaces of the Solar Max satellite retrieved after 50 months in space. They found six small holes per square foot in some areas, most of them apparently caused by impacts with paint flakes from other spacecraft.
The first operational spacecraft damage attributed to debris occurred in 1983, when the shuttle Challenger was hit by something in orbit that left a crater on one of its 5/8-inch-thick glass windows.
Scientists found components of white paint fused into the pit. They concluded the orbiter had hit a flake less than .01 inch in diameter, traveling two to three miles per second.
And on its mission last month, the shuttle Atlantis’ window was struck by something still being analyzed.
But collisions are still rare in orbit, according to Don Kessler of Johnson Space Center in Houston, dean of space debris studies, who has been watching orbital hazards since 1963. Collisions may become significantly more likely in the 1990s, he said.
This is because, as collisions happen, each creates many times more particles than mere explosions or breakups. Coming together at 22,000 m.p.h., “because of the tremendous pressures and temperatures generated in that instant, aluminum and other metals become actually fluid,” said Jeanne Lee Crews, manager of the space center’s Hypervelocity Impact Research Laboratory, where she uses gas-powered guns to simulate cosmic crackups.
That causes a spray of millions of small pieces, like droplets, many times more than a breakup or explosion of the same mass would create.
At some point, Kessler said, collisions will become so numerous they will begin a kind of chain reaction of ever more collisions and fragmentations.
“Perhaps around 2050 or so,” he said, the junk might reach “a critical density of matter in space and essentially it would grind itself to dust, and low Earth orbit would become unusable.”
Efforts are under way worldwide to hold debris to a minimum, through improved spacecraft design and other measures, as well as to protect spacecraft with shielding.
One step, for example, followed U.S. concerns years ago when it was found that six orbiting U.S. Delta rocket second stages had exploded, the last in 1981, apparently as a result of metal failure that allowed residual fuels to mix. Engineers since have modified the rockets to prevent breakups.
Also, the Soviet Union’s practice of deliberately destroying failed military satellites, which has added much to the debris, appears to have ended more than a year ago.
The U.S., Soviet, European, Japanese and other space programs now try to ensure that their rocket stages are emptied of fuel and pressure once in orbit, said Joseph Loftus, a top planning official at the Johnson center. That way, a collision with a small object will be no more traumatic than “a rifle bullet going through an empty soda pop can.”
To protect the space station, NASA has asked industry to develop, at a cost of $15 million to $20 million, a ground-based radar system that could spot a dime at an altitude of 360 miles. It would track some but not all small pieces of orbital debris that could threaten the space station.
