SPACE shuttle Discovery, now orbiting Earth, carries a little experiment that should help minimize a growing space flight hazard - orbital junk. It's a set of small aluminum spheres. Discovery's crew plans to release them Wednesday, the seventh day of this eight-day flight.
Left behind on orbit, the spheres will help engineers in fine-tuning the radars that keep watch on the great trash heap in the sky. Big junk, like a disused satellite, is easy to spot. It's the millions of small fragments that are hard to track. Yet they can damage spacecraft. Impacting at orbital speeds, they pack the punch of a rifle bullet. The spheres will provide targets of known size and composition. Engineers can use them to learn more about the kind of radar ``signatures'' the small stuff produces.
Thus, while the Orbital Debris Radar Calibration Spheres may be least in sophistication among Discovery's experiments, their role is important for many manned and unmanned missions in the future.
At press time Sunday, the astronauts were busy with more immediate tasks. They tended the dozen experiments in the Spacehab commercial laboratory in Discovery's cargo bay. And they were preparing to try again to release the wake shield satellite whose hard-to-see status lights had delayed release Saturday.
Generally, Discovery's mission has gone smoothly after an on-time launch from the Kennedy Space Center in Florida at dawn Thursday. The crew, for one thing, prepared for amateur radio contact with schools.
Cosmonaut Sergie Krikalev - the first Russian member of a shuttle crew and a licensed radio ham - received final approval to talk to students in his homeland. Although he has a Russian license, he is on board an American spacecraft. It's a situation international ham radio rules had not anticipated. However, after months of negotiation, the Russian Ministry of Posts and Telecommunications and the Federal Communications Commission gave final approval Friday. It was a minor, but potentially embarrassing problem, that the United States State Department ``wanted to whip,'' according to Peter Smith, the National Aeronautics and Space Administration's (NASA) director of international relations.
The menace of space debris is another problem that nations concerned with space are increasingly determined to whip. Since it endangers unmanned satellites as well as manned craft, it affects all who use near Earth space. Determining what's actually out there is an important step in deciding how to design spacecraft to resist damage as well as to avoid making unnecessary junk.
The North American Aerospace Defense Command has tracked space trash for over two decades. The catalog includes such ``momentos'' as a glove lost in the 1960s by former astronaut Neil Armstrong as well as lost tools and remains of rockets and old satellites.
However, the catalog contains only about 7,000 objects. Analysts figure there are actually more than three million objects too small to have made the catalog that still could cause damage.
NASA and the US Space Command are developing a ground-based radar capability to track objects a small as a centimeter across. Radars at Millstone Hill, Ma., and Eglin Air Force Base in Florida will use Discovery's aluminum spheres as practice targets. Experts feel now that it isn't practical to try to clean up the junk.