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Astronomical hazards of orbiting space junk

FIVE times faster than a rifle bullet, able to cream a satellite with a single blow, space junk is an orbital menace. And as though shrapnel from exploding rocket cases - such as the spent Ariane stage which blew up last Nov. 13 - weren't enough, new forms of junk may soon join the orbital clutter. They include ``space burials'' of cremated remains and so-called space art objects, whose diaphanous substance may not endanger spacecraft but whose highly reflective glare would ruin optical astronomy.

Having polluted Earth's waters, defaced the landscape, and dirtied the air, careless human activity now seems bent on literally littering the heavens.

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Humanity has sent over 16,800 objects into orbit since the space age began in October 1957. Many have reentered the atmosphere or, in a few cases, have been recovered by shuttle astronauts. Many others are still in space. The North American Aerospace Defense Command (NORAD) tracks roughly 6,000 orbiting objects, of which 72 percent are junk and only 5 percent are working satellites. NORAD doesn't usually track objects smaller than 8 centimeters (3.2 inches) across. Sensitive optical studies, however, have identified some 40,000 bits of debris about the size of golf balls. The number of smaller particles is unknown but is believed to be many times larger.

The fragments and particles generally result from debris abandoned by astronauts, from collisions between old satellites and between larger debris pieces, and from explosions of fuel and other chemical residues in old rocket cases after long exposure in space. This kind of debris is an ever-present hazard in low Earth orbit. Even a paint fleck does significant damage when it rams a spacecraft at orbital speeds of 4 to 5 miles a second.

Orbital decay eventually brings much of this material into the atmosphere where it burns up. But the supply is constantly replenished while the total amount slowly builds up. Satellites believed lost to orbital collisions include the US Pageos balloon satellite (1975), the European Space Agency GEOS 2 (1978), and the Soviet Cosmos 954 (1978) and Cosmos 1275 (1981).

While we can't use space without creating junk, some kinds of debris can be avoided. The 19 antisatellite (ASAT) weapons tests, which the Soviets conducted through June 1982, and US ASAT tests - such as that which destroyed the Solwind scientific satellite in September 1985 - added large amounts of debris. The Soviets now have a self-imposed moratorium on such tests, while Congress is restraining the Pentagon from continuing US ASAT testing.

Rocket-case explosions are also avoidable. Seven abandoned US Delta rocket second stages exploded after prolonged space exposure before the spent casings reentered the atmosphere. Design changes now ensure that such explosions won't occur again. Frederick d'Allest, president of Arianespace, has said that the explosion of the Ariane stage last fall could prompt comparable design changes for the Ariane rocket family, too, according to the industry journal Aviation Week.

Meanwhile, and with US Department of Transportation approval, the Florida-based Celestis Corporation wants to orbit cremation ashes in 150 kilogram (331 lbs.) satellites. Besides potentially creating more debris, these burial satellites would add to the light pollution that badgers astronomers. Their bright trails, visible to the unaided eye, would ruin many astronomical observations.

The space art with which the Soci'et'e Nouvelle d'Exploration de la Tour Eiffel plans to celebrate the Eiffel Tower centennial in 1989 would be even more pernicious. The leading concept is a tube of Mylar plastic connecting 100 plastic spheres. The whole would appear as a ring of 100 stars - each twice as bright as the Pole Star. The ring would be about the size of the full moon. A backup concept would employ a curved reflecting sail which would focus sunlight onto a rotating cross with a bright center.

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Either object would make deep space astronomy impossible when it was anywhere in view. Moreover, were a telescope using a sensitive electronic light detector to look at such ``art'' inadvertently, the detector could be irreparably damaged. Since there are only about 10 such custom-made detectors in the world, the loss to astronomy would be considerable.

NASA and its sister agencies in other space-faring countries are exploring ways to curb the orbital junk hazard. Meanwhile, those who would add to space clutter should heed the dictum of the International Astronomical Union that ``no group has the right to change the Earth's environment in any significant way without full international study and agreement.''

A Tuesday column. Robert C. Cowen is the Monitor's natural science editor.

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