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Do satellites crash into each other?

As I stare into the beautiful dark sky above my home in Hawaii and see the stars and satellites, I ponder the possibility of “space accidents.” With all those satellites, are there any collisions? Who oversees all those orbits? Is it just a stellar free-for-all? — Roy Orbits Son

No, but it’s not iron discipline either. To date we’ve been content to let just about anybody heave stuff into orbit, requiring only minimal reporting for most launches. But with increasing commercialization of space, things are starting to get crowded up there—the Union of Concerned Scientists lists 898 active satellites, operated by everybody from the U.S. to Luxembourg. Given the vastness of space, even in earth’s immediate vicinity, it’s not like we’re talking bumper-to-bumper traffic.

But consider:

(1) Those 898 satellites constitute only a fraction of orbiting objects. The North American Air Defense Command (NORAD) currently tracks about 13,000 spaceborne items, mostly junk. It’s likely hundreds of thousands more bits have escaped detection.

(2) Satellites are expensive—the huge ones, like Europe’s Envisat, can cost billions, and just putting something, anything, into orbit is likely to run you between $50 million and $400 million.

(3) Orbiting objects travel at tens of thousands of miles per hour. If two collide, they’re both going to be moving at a good clip, so the net impact speed of a glancing blow won’t necessarily be that high. But even if something merely sideswipes your $500 million orbiting investment, chances are it’s hosed.

In 1959 the United Nations recommended that rules be drawn up for handling run-ins among spacecraft, but no detailed regulations yet exist. The 1974 Convention on Registration of Objects Launched Into Outer Space requires signatory nations to report their space launch details to the UN. Presumably all do, but where they actually put the spacecraft is still up to their individual space agencies. There’s no international regulation on where low-earth satellites—those orbiting at less than about 1,200 miles up—can operate.

Not-so-low-earth satellites are a different story. I speak here of geostationary satellites, which travel in a special orbit that allows them to remain in a fixed location relative to the earth’s surface—a handy thing for communications and weather gear.

The geostationary orbit is a relatively narrow ring about 22,300 miles above the equator. Because you need two degrees of separation between satellites to avoid radio interference, there are only 180 slots available. You can put multiple satellites in the same slot as long as they use different frequencies; nonetheless, these slots are a coveted commodity.

Seeing a chance to cash in, a group of equatorial countries issued the Bogota Declaration in 1976, claiming jurisdiction over the space above their countries. But the declaration is ignored, since the countries have no way to enforce it. Instead, the International Telecommunications Union, a UN agency, decides geostationary claims.

A bigger challenge is space debris—defunct satellites, booster rocket parts, and fragments of both. Hundreds of close calls happen each day:

• In December 1991, debris from the Russian Cosmos 926 satellite hit Cosmos 1934, an event detected years later on analysis of old tracking data.

• In July 1996, a small French satellite called Cerise suddenly started tumbling in orbit. The cause? A piece of debris from an old U.S. rocket hit Cerise’s stabilizing boom at over 31,000 mph. Amazingly, the satellite recovered.

• In January, 2005, a piece of a Chinese rocket had a high-level meeting with a 31-year-old U.S. rocket booster.

These impacts were in low orbits, but even high orbits can be hazardous. In March 2006, a Russian telecommunications satellite in geostationary orbit was irreparably damaged following apparent impact with an unknown object. The same thing happened to a European communications satellite in 1993.

So the forthcoming space traffic control agency has its work cut out for it. I’ll volunteer to get on the horn with Luxembourg—nobody can tell me those jamokes need 16 satellites. cs

Comments, questions? Take it up with Cecil on the Straight Dope Message Board, write him at the Chicago Reader, 11 E. Illinois, Chicago 60611. Cecil's most recent compendium of knowledge,Triumph of the Straight Dope, is available at bookstores everywhere.