Friday, May 28, 2010

The sky is falling (not today, but soon)

As a civilization, we have become incredibly dependent on a vast array of orbiting satellites.

In the span of a single lifetime (my own) we've gone from having no man-made objects in orbit to the point where now we're approaching saturation point and are hugely reliant on the services they provide.

It's not that the heavens are clogged with satellites, it's that they're becoming increasingly strewn with "space junk" over which we no longer have any control.

In fact, items of space junk outnumber in-use satellites by a ratio of 336:1

There is now growing concern that it may take just one major collision between objects of any significant size to trigger a massive chain reaction that could cripple many other communications and navigation satellites.

Although much of the "space junk" currently in orbit is very small, even something as tiny as a screw can knock out a large satellite if it impacts at the right point with enough velocity.

Any major impacts would be sure to generate a cloud of much smaller pieces, each of which has the potential to rip through other orbiting objects with more energy than the bullet from a high-powered rifle. An example of this was the collision last year between an inoperative Russian satellite and a communications satellite operated by the US company Iridium. Scientists estimate that these two objects broke into more than 1,500 fragments, which are still in orbit around the Earth.

The effect of a Chinese "satellite-killer" test against an orbiting bird produced an astonishing 150,000 pieces of space-junk.

The problem and potential disaster it may produce is even greater than you might think.

Should a chain-reaction of impacts be set off, not only would this eventually render large numbers of satellites inactive but it would also create a cloud of fragments that would continue to circle the earth at that distance for many years to come. This shell of shrapnel would effectively make it impossible to replace those damaged satellites, as the new units would also be subjected to impact from the orbiting fragments.

Fortunately, the issue does seem confined mainly to satellites in low-earth orbits (LEO) which are just a thousand Kms or less above the surface of the planet. There appears to be less concern being voiced over the risks associated with satellites lodged in geostationary orbits which are about 37,000kms above the surface. This is perhaps because the area of a sphere with such a markedly increased radius is much greater and therefore the odds of an impact is dramatically reduced.

Geostationary satellites also have zero relative motion to each other and therefore the velocity of any impact would be minimal.

So what happens if this chain reaction does occur?

Well the vast majority of communications satellites, tend to be geostationary and would thus avoid the resulting mayhem. However, the networks associated with satellite telephones, GPS navigation and some kinds of military surveillance could be dramatically impacted.

Even the loss of the GPS network would pose a major problem to the world's transport services, forcing airlines, shipping and other long-distance craft to revert to older, less accurate navigational systems.

There is a small chance that the international space station may also have to be evacuated for fear of damage from the resulting space debris.

So yes, one day, when you look up, you might find that the sky is falling and the first you may know about it is when the sat-nav system in your car goes deathly quiet.

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