Space debris or Space junk is the accumulation of discarded launch vehicles, decommissioned satellites, & parts of a spacecraft that floats around in space and causes a risk of collision with functioning satellites or space stations. 

Space debris is the result of launching objects from the earth. Some of these objects remain in the orbit, while some debris in the lower orbits re-enter the atmosphere after a couple of years and burn up on re-entry and never reach the ground. 

When two satellites collide accidentally or inadvertently with each other, they can smash apart into thousands of new pieces, which would result in a chain reaction where even more objects will collide and create new space junk which will eventually render an Earth’s orbit unusable. This was a theory proposed by Donald Kessler in 1978 which is known as the “Kessler Syndrome.”

Space Junk doesn’t pose a risk to the exploration efforts that are undertaken by the different space agencies. However, the biggest danger the space debris pose is to the existing satellites that are traversing in the orbits. There are approximately 23,000 pieces of debris orbiting the Earth and they travel at speeds up to 17,500 mph which is harmful enough to damage a satellite or a space station.

Space debris flying at very high speeds are extremely dangerous for astronauts that reside in a space station. To avoid being hit by debris, hundreds of collision avoidance maneuvers are performed by the International Space Station (ISS) which keeps the astronauts safe.

List of key incidents where space debris caused irreparable damage to a satellite:

• In 1996, a French satellite was hit and damaged by debris from a rocket launched by the French that had exploded a decade earlier.
• On Feb. 10, 2009, a decommissioned Russian spacecraft collided with and destroyed a functioning U.S. Iridium commercial spacecraft. This collision resulted in adding more than 2,300 pieces of large, trackable debris and many smaller pieces of debris to the inventory of space junk.
• China's 2007 anti-satellite test, which used a missile to destroy an old weather Chinese satellite, added more than 3,500 pieces of large, trackable debris and many smaller pieces of debris to the inventory of space junk that contributed to the problem.

United Nations have asked all space organizations to remove their satellites after 25 years of the end of their mission. To ensure the proper removal of satellites, these space organizations came up with novel solutions to achieve their goal. 

Remove Debris Mission

Remove debris mission aims to tackle the problems imposed by space debris. A remove debris satellite launches out a net and traps the space debris which orbits around the earth. That net is not retrieved again by the satellite or the ISS but is nudged in the direction of the earth, allowing it to fall back towards the earth’s surface. However, this method can only be used for large satellites orbiting the earth at low altitudes as it involves collecting the space debris and dragging them back into the atmosphere where it will burn up.

Graveyard Orbit

A graveyard orbit is an orbit at an altitude of 36,050 km above the earth’s surface (higher than most common operational orbits) where decommissioned satellites are moved to reduce the probability of them crashing into other functional satellites and generating space debris.

Click here to learn more about Graveyard Orbit.