What is orbital debris?
Orbital debris is the technical term for the man made junk scattered in the space around the earth. Earth’s gravity traps these man made objects and particles into orbiting (revolving) around it. NASA estimates that the half century of space exploration has cluttered the space above the earth’s atmosphere with millions of detectable objects. Starting from dead satellite the list includes spent parts of rockets and other particles which are released during the flight of any spacecraft. The agency estimates that about 19,000 of these objects are larger than 10cm and another 500,000 particles are between 1 to 10 cm in diameter. Apart from these there are over millions of particles which are smaller than 1 cm. The US Space Surveillance network which tracks this junk has recently reported a significant increase in the past 5 years.
Does this junk pose serious threat to the space projects?
Traveling at the speed which varies from 7 to 10 km/s any collision of the debris among themselves or with any satellite will release a considerable amount of energy. Operational spacecraft are usually protected by debris shield and most of them can withstand the impact of particles which are 1 cm or lesser in diameter. The probability of collision of spacecraft with a particle larger than 10 cm is very low. The worst incident of collision took place in 2009 when an operational American satellite collided with a derelict Russian satellite. NASA consultant Donald J. Kessler has proposed Kessler Syndrome which is a situation in which a large density of the orbital junk could cause chain collisions. One collision will create more debris and increase the likelihood of further collisions. Such collisions will destroy satellites worth millions of dollars and could render space exploration unfeasible for centuries.
What will happen to the junk in future?
Most of these objects and particles will ultimately fall to earth. Because of earth’s gravitational pull the orbits of these particles are gradually decreasing. Depending on their distance from earth the period of the orbital decay, the gradual decrease in the orbits, varies from few years to several centuries. It takes few years for the debris left below 600 km to fall back while the objects left above 1000 kms will circle earth for centuries. NASA estimates that everyday at least one catalogued piece of the debris falls on earth. Most of these particles can’t withstand the heat generated during the re-entry and has so far not caused any serious damage.
What happens to dead satellites?
Ideally after their operational life old satellites are pushed to graveyard orbits. In many cases the maneuver of old satellites is difficult and they have to be left at the original orbits causing threat for the newer ones. In 2007 China destroyed a weather satellite by a ballistic missile and increased the debris. The Americans in 2008 and destroyed their spy satellite shortly before entering earth’s atmosphere. These incidents along with the 2009 collision of the American and Russian satellites have contributed in the increase of the debris. The cleaning up is difficult and will be expensive and hence the only thing that the global community could do is not to stop the increase in unnecessary waste in the orbits which are considered as useful natural resources.