SPACE JUNK
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Space Junk Orbiting
the Earth
What is space junk?
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:
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.
http://www.bbc.co.uk
