Science Forum

Everyone is aware of the solid-waste problem we are now facing. Calls for biodegradable materials, recycling, and trash-to-energy conversion fill the newspapers and airwaves. What few people realize, however, is that we are now facing a solid-waste problem in space as well as on Earth. Barbara Wood-Kaczmar, writing in a recent issue of the British journal New Scientist, calls space “a vast junkyard.” She goes on to say that, if something is not done about the problem soon, the human race could be denied the use of space within 30 years.

Space agencies estimate that there are more than 3.5 million pieces of space junk now orbiting the earth. Only about 7,000 of these are greater than 10 centimeters in size and are routinely tracked from the ground. The vast majority, more than 99 percent, are tiny flecks of paint or bits of metal ranging in size from a centimeter down to less than a millimeter. The small size of the latter does not mean they are harmless. In 1985, a paint fleck only 0.2 millimeters across struck the windscreen of the space shuttle Challenger. The pit it created upon impact forced NASA to replace the windscreen before the next launch. A similar fleck of paint, striking an astronaut’s suit outside the spacecraft, would penetrate it, killing the occupant. The shuttle Columbia narrowly missed a disaster in 1982 when a large piece of an old Soviet rocket passed it at a distance of less than eight miles. A collision would have resulted in the destruction of the shuttle and its crew.

The U.S. Space Command tracks more than 7,000 objects that are 10 centimeters or more in size. These range from wrenches to complete satellites. Less than 5 percent of the object now in space, however, are operating space vehicles. Space debris is concentrated in what are known as low-Earth orbits and occurs in bands. The densest regions are at 800, 1,000, and 1,500 kilometers altitude. Objects are tracked to an altitude of 36,000 kilometers, the geosynchronous orbit which contains most of the world’s communications satellites.

Many research satellites, such as the Hubble Space Telescope, are located at altitudes between 800 to 1,000 kilometers where most of the space junk is concentrated. Michael Shara of the Space Telescope Science Institute in Baltimore estimates there is about a 1-percent chance that the Hubble Space Telescope will be struck by debris. A 10-centimeter fragment would destroy it while one as small as 1 centimeter would cause serious damage.

Who is to blame for the mess in space? Most can be placed at the doorstep of the U.S. and Soviet Union and more than half is the result of accidental or deliberate explosions. Between 1973 and 1981, for example, seven American Delta rockets exploded in orbit before their manufacturer, McDonnell Douglas, could correct the problem. Between 1964 and 1986, the deliberate destruction of 34 satellites for security reasons was carried out by the two superpowers. This alone added more than 2,000 fragments to the total. In recent years, other nations have started adding to the problem with the single worst incident involving a European Space Agency Ariane rocket. The explosion created 465 fragments of 10 centimeters or greater and an estimated 2,300 smaller particles. The debris eventually spread out over the original orbit forming a shell around the Earth.

The formation of a shell of debris from the Ariane rocket illustrates a problem that has space officials worried beyond the dangers presented by the original fragments themselves. In low-Earth orbit, larger fragments are continually colliding with the millions of smaller bits and pieces present generating yet smaller particles. One hypothesis speculates that these secondary collisions will snowball into a cascade effect known as the Kessler Syndrome. The end result would be a nearly impenetrable belt of small debris around the planet that would make space flight all but impossible. Kessler, a researcher with NASA, says there is a “critical mass” of space junk that must be in orbit before his syndrome goes into effect. NASA estimates it will take place within the next 50 years. Two researchers at the Technical University of Braunschweig, Germany, believe it could happen much sooner. Dietrich Rex and Peter Eicher say only twice the present population of 70,000 fragments of 1 centimeter or larger are required. This, they say, could occur within 20 years. Kessler tends to split the difference between the two estimates and says that, “We could become Earthbound within 30 years.”

Space debris is a much more serious risk for the proposed space station, that hopefully will be in orbit for 30 years, than it is for shuttle flights lasting only a few days. The space station, Freedom, will operate at 463 kilometers, just below one of the peak densities for debris. Small particles would jolt the station and could cause pinhole leaks. Debris larger than 5 centimeters would puncture the walls as it penetrated and exited the space station causing a catastrophic drop in cabin pressure. The station will be equipped with sensing devices that will warn the occupants of the approach of larger pieces of debris allowing them to escape to heavily-shielded “stormshelters” before collision. If the station was too badly damaged, they would then have to await rescue by shuttle.

Nations with no interest in launching space vehicles are more concerned about debris falling back to Earth. When NASA’s Skylab fell back to Earth in 1979, plenty of warning was given as debris was strewn over a 1,000-kilometer long path across Australia and the Indian Ocean. No one was hurt although 500 large fragments hit the Earth at supersonic speed. Neither superpower gives any information about military satellites. The U.S. made no mention of a KH11 military satellite that broke up in March of this year although the fragments could have landed in Europe. The Soviets were equally uncommunicative about a satellite with a nuclear power plant that fell in Canada some years ago.

The U.S. and Soviet Union have 56 nuclear-powered satellites in orbit between 800 to 1,000 kilometers. The majority are Soviet spy satellites that are placed in an 800-kilometer “parking orbit” at the end of their mission. Their power plants still have highly radioactive nuclear fuel that will be released when the satellites eventually break up in the atmosphere. Nicholas Johnson, an expert on Soviet satellites, says it is a “virtual certainty” that one of these satellites will eventually collide with space debris releasing radioactive elements into the ring of debris now circling the planet.

The U.N.’s Committee on the Peaceful Use of Outer Space is preparing guidelines for the reduction of space debris that should be complete by 1992. The fact is, however, that it will take the cooperation of the nations with space capability to effect any change. At the moment, this does not seem to be a likely prospect.

Clair Wood, a science instructor at Eastern Maine Technical College, is the NEWS science columnist.