Space debris or space junk/waste is the collection of unwanted and defunct parts of the old satellite, rockets etc. They orbit around the earth with very high velocity (thousands of miles per hour]. Hence, even if they are as small as 1 cm in size, their impact on other valuable objects orbiting earth is huge. They can collide and damage them. They pose even a greater threat to space crews.
The amount of space debris present in the lower earth orbit (LEO) has already exceeded the critical point. They are damaging the other critical objects like satellite, since their orbits are generally overlapping in nature. The amount of debris is so high that the chances of collision are very high. These collisions are further increasing the debris. Hence, the probability of collision keeps on increasing with more debris. This scenario is referred to as KESSELER SYNDROME. Increasing amount of space junk will make space inaccessible for future generation, even if all the space launches are cancelled, the space debris will continue to grow because of collisions between the existing debris. Apart from orbit correction, there are no effective ways of protecting spacecraft from debris flying at nearly 8 km/s. The problem is the most serious in geostationary orbits used by communications and weather satellites because junk could stay there for millions of years. Geostationary orbit, which is a limited resource, may be lost in the next 20 years because of man made pollution.
To tackle the problem , the Hunter killer probe is being designed by European Space Agency to destroy all the defunct satellites. The e.Deorbit probe would deploy a Roman gladiator-style array of nets and harpoons to first trap rogue satellites and then drag them downwards until they burn up in the atmosphere. Removing between five and 10 large satellites from space each year would be enough to stop the debris cloud growing.
