Since the first satellite, Sputnik 1, was launched in 1957, thousands of space probes, satellites and telescopes have been sent into space. Just as we have created rubbish mountains on Earth, we've also accumulated a blanket of junk around the Earth.

This debris silently zooms around the globe at speeds of up to 25,000 miles per hour with altitudes ranging from hundreds to thousands of miles. NASA frequently replace windows on the space shuttle that have been damaged by objects as small as a flake of paint.

How much junk is out there?

Radar and optical monitoring can pinpoint the location of space debris only centimetres in size.

The current estimate is that there are over a million bits of debris orbiting the Earth. About 70,000 objects about the size of a postage stamp have been detected between 850 - 1,000 km above the Earth. They are probably frozen bits of nuclear reactor coolant that are leaking from old satellites.

An additional problem is that this debris is breaking up. Explosions or collisions blast the objects into smaller pieces, increasing the number of objects further. More than 124 break-ups have been verified, and more are believed to have occurred.

What are the dangers from debris?

Although most of the debris in space is small, it's travelling extremely fast. Below altitudes of 2,000 km, the average relative impact speed is 36,000kmph (or 21,600 mph).

At this speed, collision can be dramatic:

• A 1mm metal chip could do as much damage as a .22-caliber long rifle bullet

Bits this size don't generally pose a large threat to spacecraft, but can erode more sensitive surfaces and disrupt missions.


• A pea-sized ball moving this fast is as dangerous as a 400-lb safe travelling at 60 mph

Debris this large may penetrate a spacecraft. If this happens through a critical component, such as the flight computer or propellant tank, this could be fatal.


• A metal sphere the size of a tennis ball is as lethal as 25 sticks of dynamite

This debris will penetrate and seriously damage a spacecraft.

At geosynchronous altitude (35,900km), the relative speeds are lower - 720 kmph (432 mph). Geosynchronous orbit is one in which a satellite rotates around the Earth at the same rate as the planet spins. Many satellites are at this height as it means they can remain above one particular area of the world.

Junk-free zones

There are junk-free zones that are relatively clear. These are monitored and used to calculate the trajectory of spacecraft. In the past, NASA has had to adjust the flight path of space shuttles on at least eight occasions to avoid debris.

Some research suggest that the collision risk from small particles is minimal. One study showed that a craft that had been in space for more than five years was struck by particles more than 30,000 times, with no ill effect.

The Center for Orbital and Reentry Debris Studies (CORDS), located in El Segundo, California, was established in 1997 to study space debris, collision avoidance, and re-entry break up. In 1999, they estimated that 193,000kg of material re-entered the Earth's atmosphere.