Scientists Fear Space Debris Problem Worsening

April 21, 2008
By Chris Gorski
ISNS Contributor

St. Louis, MO -- In the wake of the Chinese government's destruction of one of its retired satellites in orbit last year, scientists are increasingly concerned that space debris poses a significantly greater risk to satellites than previously believed. Indeed, scientists at a recent American Physical Society meeting in St. Louis said they fear the chances of a destructive "supercritical chain reaction" collision in space are increasing.

Scientists have long been concerned about debris in space, particularly in the band between 500 to 600 miles above Earth, where many other satellites orbit. Space debris is also a problem in the lower orbits around 200 miles up, typically used by the Space Shuttle.

One phenomenon that scientists fear is the supercritical chain reaction, in which a collision between two pieces of debris creates more pieces that then collide with other debris. The result is a slow cascade of collisions that breaks existing debris into thousands of smaller pieces. Each one of those pieces poses a threat to orbiting satellites. This chain reaction problem, said David Wright, codirector of the global security program for the Union of Concerned Scientists, "is worse than assumed."

In January, 2007, the Chinese blew up the defunct satellite, Feng Yun-1C, with an anti-satellite missile, creating a cloud of debris in space. Scientists studied the explosion and determined that the NASA Standard Breakup Model used to predict the amount of debris produced by a collision underestimated the actual number by a factor of three.

In addition to the explosion occurring in the most crowded orbital zone, Wright said that because of extremely low atmospheric density at that altitude the pieces of the Chinese satellite may linger for decades before falling into the lower atmosphere and burning up.

The Chinese explosion made what was already a bad problem worse. A 2006 study by NASA scientists published in the journal Science suggested that the number of pieces of debris would continue to grow for the foreseeable future. The study based its predictions only on items in orbit at the time.

While gravity and atmospheric drag remove pieces of debris from orbit, the process is slow. In a supercritical chain reaction, collisions create more debris than those forces remove, causing the amount of debris to build up and increasing the likelihood of collisions.

Previous research has shown that a particle of the right size scoring a direct hit on a 10-ton satellite in low-earth orbit would double the amount of debris presently in the band. Now, said Wright, "the Chinese test suggests that [the impact] would be even bigger."

Currently, there is no effective method of removing such particles from orbit. Wright concluded that the best method to keep particles out of orbit is to prevent them from being created. Scientists already suggest venting gas from defunct satellites to keep them from exploding and there has been a de facto moratorium on using missiles to destroy satellites.

The de facto moratorium has now been broken by both China and the United States. The U.S. satellite destroyed in February, 2008 was traveling in a much lower orbit than the Chinese satellite, and appears less likely to cause lasting effects. According to NASA reports, the satellite was about 150 miles above the earth at the time of its destruction, and they expect that by this summer the last few remaining particles will burn up in the atmosphere.

The effect of the U.S. launch could be devastating. Wright said that "the concern now is what does that say to other countries. There is a concern that other countries will do tests." He supports international measures to prohibit the use of anti-satellite weapons. Any more debris-creating events threaten to make low-earth orbits a dangerous place for satellites, scientists fear.

ISNS contributor Chris Gorski is with the American Institute of Physics’ Discoveries and Breakthroughs Inside Science program. He is a news researcher, writer and filmmaker who specializes in science.

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