Kessler Syndrome

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Kessler Syndrome

By Wikipedia,
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http://en.wikipedia.org/wiki/Kessler_Syndrome

The Kessler Syndrome is a scenario, proposed by NASA scientist Donald J. Kessler in a 1978 publication, where the volume of space debris in Low Earth orbit is so high that objects in orbit are frequently struck by debris, creating even more debris and a greater risk of further impacts. The implication of this scenario is that the escalating amount of debris in orbit could eventually render space exploration, and even the use of satellites, unfeasible for many generations.

Debris generation and destruction

Every satellite, space probe and manned mission has the potential to create space debris. As the number of satellites in orbit grows and old satellites become obsolete, the risk of a cascading Kessler Syndrome becomes greater.

Fortunately, at the most commonly used Low Earth Orbits residual air drag helps keep the zones clear. Collisions that occur under this altitude are also less of an issue, since the energy lost in the collision results in fragment orbits having perigee below this altitude.

At altitudes above the levels where atmospheric drag is significant, lifetimes before orbital decay are much greater. Slight atmospheric drag, lunar perturbations, and solar-wind drag can gradually bring debris down to lower altitudes where fragments finally re-enter, but at very high altitudes this can take millennia.

Seriousness

The Kessler Syndrome is especially insidious because of the "domino effect" and "feedback runaway". Any impact between two objects of sizable mass spalls off shrapnel debris from the force of collision. Each piece of shrapnel now has the potential to cause further damage, creating even more space debris. With a large enough collision (such as one between a space station and a defunct satellite), the amount of cascading debris could be enough to render Low Earth Orbit essentially impassable.

The Kessler Syndrome presents a unique problem to human space travel. Space debris are very difficult to deal with directly, as the small size and high velocities of most debris would make retrieval and disposal impractically difficult. Given thousands of years, most debris in Low Earth Orbit would eventually succumb to air resistance in the rarefied atmosphere and plunge to the Earth.

Avoidance and reduction

To minimize the chances of damage to other vehicles, designers of a new vehicle or satellite are frequently required to demonstrate that it can be safely disposed of at the end of its life, for example by use of a controlled atmospheric reentry system or a boost into a graveyard orbit.

One technology for the bigger fragments that can be tracked is the laser broom, a multimegawatt land-based laser that could be used to target fragments. When the laser light hits a fragment, one side of the fragment would ablate, creating a thrust that would change the eccentricity of the remains of the fragment until it would re-enter harmlessly.