On 10 February 2009, a decommissioned "Cosmos 2251" satellite and an operational "Iridium 33" satellite collided at an altitude of 790 km in low Earth orbit (LEO), a zone heavily populated by communications satellites. The collision created two distinct clouds of more than 800 pieces of space debris--man-made objects in orbit that no longer serve a useful purpose. It was the first collision of two intact spacecraft and the fourth known accidental hypervelocity collision caused by catalogued space debris.
You may wonder why the news about satellites fragmenting to space junk, a hundred kilometres away in outer space should be important to us. The brief answer is because we are enjoying space benefits every day here on Earth, whether we realize it or not. Contrary to common perceptions, most satellites in orbit look down to and cater for the Earth, rather than up to outer space. Thus, communications satellites have shrunk the planet to a "global village" through broadcasting telephone and television signals, providing internet linkages, and supporting financial transactions, no matter how remote. Global navigation satellites determine our exact location on Earth with an accuracy of up to a few metres and have now become ubiquitous in our lives, from aviation, geology, ground and maritime transportation, to architecture, car navigation and golf. Weather satellites prompt us every morning what to wear on a given day. Earth observation satellites bring enormous societal benefits through providing valuable data about the planet's ecosystem and producing the evidence necessary for informed decision-making. They also help us map places otherwise inaccessible to humans and facilitate relief efforts during disasters and other emergencies. In the aftermath of the devastating Cyclone Nargis in April 2008, relief efforts on the ground in Myanmar greatly benefitted from satellites in space, which restored vital communication links and produced space-derived imagery of the affected areas.
Space technology has become an indispensable part of the world's infrastructure, playing a crucial role in international development, security, and environmental monitoring and protection. Our dependence on satellites became evident in May 1998, when the malfunctioning of a single communications satellite resulted in 30 million pagers going silent, credit card payments failing, and some radio and television networks going off the air. According to the 1967 "Outer Space Treaty", outer space is legally "the province of all mankind". The continued ability of humankind to explore and use that province is vital to our way of life.
Around a thousand operational satellites of more than 40 countries are now orbiting around the Earth. Nearly eight dozen objects are launched into space every year. After serving humankind, all those satellites are doomed to die out and become space junk. Today's satellite is tomorrow's space debris. There are more than 300,000 pieces of space junk between 1 and 10 cm, and over 17,000 greater than 10 cm in diameter. In 2007 there was a 20 per cent increase in the number of traceable space debris. When the size and amount of this debris is calculated relative to the average velocity it travels (7-8 km/ sec), then one can imagine how both polluted and dangerous the space environment has become. While only 1 cm of debris moving at 10 km/sec (equivalent to the energy of a bowling ball hitting you at 520 km/sec) can cause catastrophic failure of an active satellite, metal junk of the size of an orange is as fatal as 25 sticks of dynamite. The threat of lethal impact from space debris is such that astronauts of the heavily shielded International Space Station (ISS) were forced to temporarily shelter in the Soyuz capsule on 12 March 2009, when a piece of debris 13 cm in diameter was belatedly projected to pass close to ISS. Now visualize the impact of the collision between the Cosmos (560kg) and the Iridium (900kg) satellites at a velocity of 11km/sec. …