Space junk such as fuel tanks, lost tools and parts of derelict satellites has rapidly become a major problem in recent times. According to the NASA estimates; there are currently at least 500,000 objects between one and ten centimetres orbiting the Earth; there are more than 100 million objects up there that are smaller than one centimetre.
The Problem of Orbital Debris
Orbital debris is the man made junk scattered in the space around the earth. Earth’s gravity traps these manmade objects and particles into orbiting (revolving) around it. As per the NASA estimates, half century of space exploration has cluttered the space above the earth’s atmosphere with millions of detectable objects.
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. Thus, majority of the estimated millions of pieces of space debris are small particles, less than 1 centimetre (0.39 in).
These include dust from solid rocket motors, surface degradation products such as paint flakes, and coolant released by RORSAT nuclear powered satellites. Starting from dead satellite the list includes spent parts of rockets and other particles which are released during the flight of any spacecraft.
How big is Risk?
Orbital debris poses a threat to the approximately 1,000 operational commercial, military and civilian satellites orbiting the Earth.
The world’s first space smashup occurred in 2009 when a working Iridium communications satellite and a non-operational Russian satellite collided 789 km over Siberia, generating thousands of new pieces of orbital debris.
The crash followed China’s destruction in 2007 of one of its defunct weather satellites as part of a widely condemned anti-satellite missile test.
Since these particles travel at a speed of 7 to 10 km per second, any collision of the debris among themselves or with any satellite will release a considerable amount of energy.
We should not that the Operational spacecrafts are usually protected by debris shield and most of them can withstand the impact of particles which are 1 cm or lesser in diameter and the probability of collision of spacecraft with a particle larger than 10 cm is very low.
The probability of a collission of a space craft with a particle more than 10 cm is very rare. But a large density of the orbital junk is capable of causing chain collisions. This has been named the “Kessler Syndrome” by NASA consultant Donald J. Kessler. 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.
Does this junk ultimately falls on earth?
Yes. Most of these objects and particles will ultimately fall to earth. This is because of the fact that 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. Most of these particles can’t withstand the heat generated during the re-entry and has so far not caused any serious damage.
Graveyard orbit is a Supersynchronous orbit where spacecraft are intentionally placed at the end of their operational life. 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.