Ken Tapping, January 31, 2007

On any clear, dark evening, a few minutes of observing will come up with at least one starlike object moving slowly across the sky. You are seeing objects we have put into orbit, either a satellite or a booster rocket. On October 4, 1957, Sputnik, the first manmade satellite went into orbit. Today, artificial satellites are commonplace. They help with navigation, communication, science, mapping natural resources, monitoring the weather, studying the environment, broadcasting, spying, and lots of other applications. They are now essential parts of our everyday lives. The biggest of them is the International Space Station.

Satellites orbiting a few hundred kilometres or less above the Earth are moving through the thin, upper reaches of our atmosphere. At speeds of around 30,000 km/h, the atmosphere exerts a weak but continuous drag on the satellites, slowing them down. Their orbits get lower and lower until they dive down into the lower atmosphere and burn up. At higher altitudes, the atmosphere is so thin the drag force is negligible, and objects can stay in orbit for decades, centuries or millennia, or longer. When one of these satellites fails or is switched off, it remains in orbit, becoming what is known these days as "Space Junk", a serious hazard to other satellites, spacecraft, and astronauts.

Dead satellites are not the only junk items up there. When a satellite is launched, the final booster stage of the launch rocket generally goes into orbit with it. Quite often these contain some remaining liquid fuel, which eventually boils, and like steam in a boiler without a safety valve, may blow that booster to bits. In addition to satellites and boosters, there are assorted adapter rings, springs and other pieces of metal that were used to join the satellite to the booster, all orbiting our planet. Moreover, satellites have been launched into many different orbits, and explosions and collisions have ejected fragments into still other orbits. In addition to these are some gloves, a camera or two, and at least one golf ball. To make things worse, various countries have conducted space war experiments, where a satellite is attacked and destroyed by another. As a result, our Earth is now surrounded by many thousands of bits of metal and plastic, nuts, bolts, larger objects, bits of booster and dead satellites, all moving at around 30,000 km/h, in all directions.

Pictures of pieces of space junk taken from the shuttle or space station usually show small pieces of material drifting slowly past, turning over and over. That material is moving in the same direction as the spacecraft. Stuff coming the other way will be passing by at 60,000 km/h. Being hit by a piece would be very serious. A fleck of paint moving at these speeds would have the energy of a rifle bullet. A bolt hitting the shuttle at such speeds may well destroy it. Unfortunately, at the moment there is nothing we can do. There is no catcher's mitt for objects moving at orbital speeds. All we can do is avoid dumping any more. A friend told me the main manmade landmarks in the Arctic and Antarctic are piles of old oil drums. Now we are treating our space neighbourhood the same way.

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Ken Tapping is an astronomer at the National Research Council Herzberg Institute of Astrophysics (NRC-HIA), and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9 Tel (250) 493-2277, Fax (250) 493-7767,
E-mail: ken.tapping@nrc-cnrc.gc.ca