Increase in space debris poses risk

A successful Chinese missile test last year that destroyed one of its own aging satellites has substantially added to space debris around Earth, increasing the danger that a chain reaction of colliding space junk could threaten parts of the world’s satellite network, scientists said today.

The threat is debris would begin slamming into other debris, creating a cascading effect called “super-criticality,” according to scientists addressing the American Physical Society conference here this week.

“Debris in space is already a problem,” said David Wright, a senior scientist with the Union of Concerned Scientists in Cambridge, Mass. “But it’s potentially a very big problem.”

Geoffrey Forden, an MIT physicist and expert on the Chinese space program, said the danger from space debris is actually more of a worry than the threat that the Chinese, or some other country, could intentionally cripple American space assets with anti-satellite weapons.

Forden argued that America’s redundancy in space satellite systems makes it almost “invulnerable” to that kind of attack. And it would be relatively easy to spot the Chinese readying a launch.

On the other hand, “we are in danger of a runaway escalation of space debris.”

According to Wright, the Chinese shoot-down on Jan. 11, 2007, added more than 2 million pieces of debris in low-Earth orbit, which is where most satellites are located.

Because there is already so much debris – more than 150 million pieces, most of them less than 2 inches across – even if nothing more is added, the amount will still increase by a factor of three in the next 200 years due to the fragmentation of pieces from collisions and other reasons.

That could be a low figure if more anti-satellite tests take place. Destruction of a single 10-ton satellite can contribute up to 15 million pieces of junk, thousands of them more than a foot across. Even now, a satellite orbiting Earth passes within 60 miles of a piece of junk several thousand times a day and has a 1% chance each year of getting hit.

“Space is not a big, empty place,” Forden said.

In February, the U.S. demonstrated its own anti-satellite capability, shooting down a dead spy satellite. But that didn’t pose the danger of the Chinese test because the U.S. satellite was in a low enough orbit – 125 miles up – that the debris will soon burn up in Earth’s atmosphere.

The Chinese missile struck a satellite orbiting 530 miles above Earth, meaning the debris will remain in space for hundreds of years, the scientists said.

Still, Forden called the Bush administration decision to shoot down its satellite “bad policy” because it could encourage other nations to build their own anti-satellite weapons.

The U.S. began to recognize the threat from space junk about a decade ago, Wright said. Since then, it has been taking measures to reduce the amount of new debris. Those efforts had largely succeeded up until the Chinese demonstration.

Forden said the threat of super-criticality is a warning that it’s time to treat space not as a vast junkyard, but as a natural resource that must be protected the same way we are learning to protect resources on Earth.

“We’re fortunate we haven’t really screwed things up yet,” Wright said. “But the Chinese test brought home how quickly this could get out of hand.”

john.johnson@latimes.com