By Mitali Goel
Humans have been sending enormous amounts of satellites, rovers and rockets beyond the sky, moving around the Earth, to our moon Luna and to the planets in our system and their moons. But what happens once those machines stop functioning?
Space junk, also called space debris, comprises all the old non-functioning satellites and spacecrafts which are left out there in space, the broken or separated parts of rockets formed during the disintegration stage. The debris at the other planets might be too far away to cause any trouble but the increasing amount of junk in the Earth’s orbit is something to be dealt with.
Space junk is increasing every year and is crowding the Earth’s orbit making it harder for astronomers to observe outer space and increasing the risk of damage to satellites, telescopes and the ISS due to collision. New launches are making the space more crowded. Space junk increases the possibility of collision which further adds to debris.There are around 2,000 active satellites in orbit while 3,000 dead ones. Most of the debris is found in the lower Earth orbit, upto 2,000 km from the surface, while some can be found in the geostationary orbit, 35,786 km from the surface. The size of debris ranges from intact large satellites to undetectable smaller-than-1mm pieces. There are around 34,000 pieces larger than 10cm and 128 million pieces less than 1 mm. The smallest of pieces can be harmful to active man-made objects because of their breakneck speeds. In 2006, for example, a tiny piece of space junk collided with the ISS, taking a chip out of the heavily reinforced window. Satellite operators can’t steer away from all potential collisions, because each move consumes time and fuel that could otherwise be used for the spacecraft’s main job.
Junk lower in the orbit may fall back to Earth after some years while the ones that are a little higher may take upto hundreds or thousands of years to fall back. Smaller pieces burn in the atmosphere itself while a few big objects fall intact on Earth which can be dangerous.
So what has been done so far and what else can be done to tackle it?
One of the ways to reduce space junk is to program the orbit of satellites in a way that will gradually take them lower, at the end of their functioning life, enough to be in the atmosphere’s drag which in turn will bring it back to Earth.
Moreover, satellites can be tugged and towed lower in the orbit for them to reenter the Earth.
This method can also be used to send those objects to the graveyard orbit (orbit farther from the satellites to avoid collision). However, graveyard orbits have not been of much help because debris can deorbit with time and cause the same problem again.
Another potential method is to use lasers from ground, hitting the debris, slowing them down and eventually bringing them under the atmospheric influence. The momentum from the photons can easily impart thrust on the smaller debris for them to change orbit. NASA found that the impulse could be 1mm per second changing the junk’s course by 200m/day provided the laser is kept on it for a few hours. Although, at times the debris might disintegrate into smaller pieces and add to the problem instead by increasing the amount of junk; smaller pieces are also hard to detect.
Several combined techniques like net, harpoon and clamping mechanism are being studied to capture space junk. The most successful venture so far is the RemoveDEBRIS plan, equipped with a net, a harpoon, a laser ranging instrument, a dragsail, and two CubeSats (miniature research satellites). The mission was launched on 2 April 2018.
Although some national organisations are employing trial missions to clear our space junk, there are no concrete international laws regarding the ownership and clearance of debris. More definite and stronger execution is necessary to get rid of that cloud of trash encircling the Earth so that space exploration can be continued without any limitations and hazards.