What is the risk from Space Debris? What is NASA doing about Space Debris? What is the Space-Based Surveillance System?
Concern is growing about the amount of "space debris" or "space junk" - defunct spacecraft, discarded pieces of rocket launching systems, and particles of liquid coolant - that is in orbit around the Earth. A recent report by NASA suggests that there about 500,000 objects that are centimeter-sized or larger in orbit, accompanied by over 10 million smaller fragments.
"The current space environment is growing increasingly hazardous to spacecraft and astronauts."
-Donald Kessler, NASA Orbital Debris Program.
Even though many of the orbiting objects are tiny, they could still cause considerable damage to a satellite if they collided with it at speed. The momentum of a colliding object is the product of its mass and its speed. The more momentum the object has, the greater the impact of the collision. Most orbital collisions happen at high speed - typically around 10 km per second - so even a tiny fragment of rock or debris can spell disaster.
In addition to all the fragmented junk, the sheer density of satellites orbiting our planet is also beginning to cause a problem. In 2009, two satellites - one belonging to the US company Indium and the other a Russian satellite - collided above Siberia. Scientists warn of reaching a "tipping point", above which it is not safe to put any more satellites into orbit because the traffic orbiting the Earth is simply too high.
In 1993, a group of organisations from 12 countries came together to form the Inter-Agency Space Debris Co-ordination Committee. Their aim is to assess the problem of space debris and take steps to rectify it.
Monitoring and Collision Avoidance
The US Department of Defence, recognizing the danger posed to US satellites, spacecraft, and the International Space Station (ISS), commissioned the construction of a space surveillance and tracking system. The Space Based Surveillance System (SBSS) will use a network of satellites, combined with ground-based sensors, to keep track of the positions of satellites and other orbiting objects. If satellites are discovered to be on a collision course, their operators can use the satellites' boosters to move them out of harm's way.
Several solutions have been proposed, including nets, giant magnets, or probes that could join onto large pieces of debris to steer them towards the atmosphere where they can burn up. However, all of these ideas are still in the early stages.
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