Expanding clouds of debris from a collision between two satellites over Siberia on Tuesday comprise “an elevated risk of a collision with the International Space Station in coming weeks” according to a leaked memo from NASA. This could just blow the global financial crisis off page one for a day or two!

In an extreme scenario, the three space persons of Expedition 18 currently resident in the giant target — okay, make that the space station — could have to scram themselves back into the Russian Soyuz transport vehicle which brought them there in December and isn’t due to drop them back to earth for another two months.

So what happened, and is the menace of space junk out of control? The short answer is: “Yes it is.”

On Tuesday, Iridium 33, one of a constellation of 66 working communications satellites supporting the Iridium global satellite telephone and data network, collided 790 kilometres above the arctic with a defunct Russian spy satellite, Kosmos 2251, which was launched in 1993 and worked for about two years.

It was a case of 900 kilograms of spy satellite whacking into 560 kilograms of phone satellite at an estimated 350 kilometres an hour difference in velocity.

This was a glancing blow by two satellites doing around 29,000 kilometres-an-hour, but it worked a treat, creating two expanding clouds of debris in which over 600 individual bits of metal are big enough to leave a radar trace.

Why is the space station at an even smaller, yet elevated, risk of a collision?

While it only orbits at around 354 kilometers altitude, the ISS could strike parts of the debris clouds as they “decay” in orbit and fall lower, or worse, encounter debris from new collisions involving several hundred military and scientific and commercial satellites known to be in orbits even closer to the those followed by Iridium 33 and Kosmos 2251.

Iridium 33 is one of 65 other Iridiums in near identical orbits, and the debris could have a cascading effect on the rest of the “constellation”.

When might this happen?

It could be days or months. NASA is trying to build up an accurate picture of the dispersal and decay rates of the debris.

Even a very tiny piece of metal from the wreckage could strike the ISS with enough velocity to cause serious damage. The ISS can shift its orbit slightly if it gets advance warning of anything larger than 10 centimetres across, which is the traceable limit for the the space networks of the eastern and western world.

How much of this junk is up there?

NASA says it is tracking 18,000 objects of a 10 centimetre cross-section or more. The higher orbiting items could remain up there for thousands of years, but those under 500 kilometres usually drop back into the atmosphere within several years, only to be replaced by even more space junk.

How often do satellites collide?

This is the first case of a destructive collision involving a working satellite. There is indirect evidence of a grazing encounters at low speed between two geosynchronous satellites, and mathematical models infer regular collisions between tiny pieces of debris.

Why is small space junk dangerous?

Kinetic energy. Mass times velocity equals a nasty hole, rather like the ones left by a high powered bullet or armour piercing shell.

Is space junk regulated?

No, it is Dodge City circa 1850 up there.

Doesn’t anybody care?

The major space powers now equip large satellites like the unmanned disposable supply vehicles that dock with the ISS and even some commercial payloads with small thruster motors that can de-orbit a dying or discarded satellite with accuracy away from land or shipping.

The satellite graveyard of choice is the mid- to sub-Antarctic south Pacific, which often gives Fijians a great view of multiple fireballs scorching across the sky, no doubt one day frightening the daylights out of any lone around-the-world sailor who blunders into the drop zone.

Astronomers care too, as space debris can interfere with deep sky observations, and they have been influential in getting de-orbit systems fitted to some payloads.

Is there a solution to space debris?

Not so far. Proposals include using directed energy weapons (meaning top secret death rays, high power lasers and focused microwave devices) to vaporise debris, or hit it with enough energy to make it fall out of orbit without leaving even more fragments behind.

But nature could provide a partial solution on Friday, 13 April, 2029 when Earth crossing asteroid Apophis comes by at less than the height of the geosynchronous satellites (37,786 kilometres) which may wipe out some debris.

Depending on how low that encounter turns out to be, Apophis can theoretically be deflected into an orbit which would collide with earth on 13 April, 2036, in which case we or our descendants will have a different debris problem to cope with.

Crikey welcomes your dumb questions, and will find someone smart to answer them. Send your suggestions to [email protected] with “clarifier” in the subject field.

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Peter Fray
Peter Fray
Editor-in-chief of Crikey
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