AMONG the dangers space-walking astronauts faced during the shuttle Endeavor's maiden flight last month was the remote possibility of being hit by orbiting trash. Or was it that remote?
Technicians later found that something had struck Endeavor's left cockpit window hard enough to gouge out a small pit. At the relative speeds of such encounters, even a paint flake carries the punch of a rifle bullet. This incident occurred less than a year after two shuttle missions in a row had orbital encounters of a different kind. Crews on board Discovery and Atlantis had to dodge old rocket debris, respectively, in mid-September and late November.
The growing space-junk hazard is forcing the United States National Aeronautics and Space Administration (NASA) to think again about the safety of the space station it plans to build in the midst of the orbital litter.
Congress's General Accounting Office is about to release a report warning that junk can be a substantial hazard for space station Freedom. NASA station officials, for their part, say they are taking the threat seriously. They expect to install additional shielding after Freedom is built if experience shows it to be needed.
The wisdom of NASA's planning is likely to be debated as Congress goes over the space-station budget. But the fact that the space-junk danger has come to the fore in space-station planning points to a larger concern. Congress's Office of Technology Assessment issued a report two years ago that highlighted the need for space-faring nations to agree on common measures for curbing orbital junk.
As Ray A. Williamson, who led the OTA study, later observed, "Unless all space-faring nations sharply reduce the amount of debris they leave in orbit, space will eventually become too dangerous for spacecraft or people."
Outlining his concern last fall in the US National Academy of Sciences magazine, Issues in Science and Technology, Mr. Williamson noted that the US Space Surveillance Network tracks about 7,000 orbiting objects, of which only about 6 percent are active spacecraft. About 240 trackable objects, mostly debris, join the list annually. Williamson also notes analyses suggesting that there may be 30,000 to 70,000 untracked objects larger than a centimeter across in low-earth orbit.
Then there is an unknown, but presumably much greater number of tiny particles along with the larger junk. Even dust-sized bits can ruin spacecraft by scouring or contaminating solar cells and other sensitive surfaces and instruments. And, Williamson warns, even particles less than a centimeter in diameter "may be capable of piercing current spacesuits."
The OTA study concluded that cleaning up near-earth space, while feasible, would be prohibitively costly. It would be better not to litter up that space to begin with.
Some steps are being taken to do this. The United States and Europe, especially, have tightened up procedures to reduce needless creation of junk. But much more definitive action is required.
Space-faring nations should work together to have an effective antilitter treaty in place by century's end, if not sooner. After all, near-earth space is as much a part of our common environment as are rain forests, air, and water.