Imagine you’re onboard a spacecraft, orbiting planet Earth travelling at 8km/s. You observe the stunning array of landscapes in front of you and you appreciate where you are when all of a sudden, you hear alarms going off, your spacecraft has been hit! Not by an alien invading Earth, nor an asteroid, but rather, a micrometeorite left behind by humans, and their previous endeavours in space.
What is it?
This is the reality of the immediate space around Earth. Hundreds of thousands of these micrometeorites whizzing around, like you, at several kilometers per second. This is known as space debris, junk or trash, and its becoming more of an issue.
Space debris is the official term for any form of debris left behind by humans in a space mission that was no longer necessary. This can be anywhere from derelict spacecraft and upper stages of rockets to tiny flakes of paint1.
Why is this a Problem?
Now you might be surprised to hear that the larger the object is the less immediate threat it poses for spacecraft and/or astronauts, but its the two ways that we see the problem: traceability and destructiveness. An upper stage of a rocket will definitely be more destructive then a flake of paint, but radar can easily track it, so we can avoid a collision with it. A flake of paint, being the largest size of a few centimeters is currently very hard to impossible to do, but it still causes quite a bit of damage. Granted, it is less damage than a larger object but lets take the following example as a reference. A bullet, roughly the same size of the flake of paint, exits a gun around 800m/s or 3000km/h. This velocity reduces due to air resistance.
The flake of paint on the other hand, travels at a few kilometers per second, and with the vacuum of space, it doesn’t slow down, so you can imagine the damage it can create to satellites.
Why will it get worse?
Now that we know about the impact of one piece imagine the hundreds of thousands orbiting Earth right now. The combination of the numerous pieces makes the space around Earth a minefield of flying bullets, a minefield that operators of these satellites have to navigate from time to time. Its only going to get worse as well due to two reasons:
More and more satellites are going up into space, meaning more rocket parts will just be floating about.
The domino effect means that once one piece collides with another piece, it will result in it breaking into smaller pieces. This will build up until there are thousands of un-trackable pieces rather than the one, leading to the Kessler Syndrome.
The Kessler Syndrome, named after NASA scientist, Donald Kessler, is a theoretical scenario where the amount debris is so high that it continually collides making more and more until there is a whole cloud of debris around the Earth, making space inaccessible to humans.
This domino effect is well captured in the graph below, where you can see noticeable increase in numbers after collisions.
Now with the threat of not being able to go to space anymore is not a nice idea to get your head around, so what are we doing to stop it?
What are we doing about it?
Well there have been multiple proposals of how to remove space debris from where there are the most pieces, the Low Earth Orbit (LEO). But, most of them are too expensive to run, leaving only 2 concepts excluding mitigation techniques outlined by ESA in 2023. Both of these ideas utilise the Earth’s atmosphere in its capabilities of burning stuff up. When an object enters the Earth’s atmosphere it heats up a tremendous amount, so much so that it creates plasma, ranging up to 8000 degrees Celsius. Now if unprotected, this object will burn up in the atmosphere and vapourises before it hits the ground. Using this principle, many companies have proposed their ideas of making these objects re-enter into the Earth’s atmosphere so that it can burn up. The first more conventional way, is by launching a satellite, where its only purpose is to slow down these large objects so that they can re-enter. Firms like ClearSpace & Astroscale are developing satellites in order to carry out these tasks.
A rather more unconventional but effective method is through the use of space lasers. First proposed in the 1970’s, space lasers would allow the de-orbiting or smaller objects (<10cm) that can still cause a lot of damage to satellites. It would work by firing a laser so that it would intercept the object and knock it off its trajectory. This would either be to avoid it colliding with other satellites, or knocking it back into Earth’s atmosphere. If there would be a space laser satellite, it would be able to fire multiple of these objects back into the Earth’s atmosphere every day reducing the amount one by one.
However, there is one issue stopping that idea becoming a reality. In the height of the Cold War, the Outer Space Treaty was signed in 1967 to avoid the use of weapons on celestial objects like the Moon and other parts. The most notable, for this part, is the destruction of other countries property in space. Hence, if a space laser were to be active, each country would need to have one, unless this issue were to be resolved, otherwise an international treaty would be violated if a space laser (from the US) would fire down a decommissioned satellite from Japan.
So what do you think we should do? Should we fire up those lasers or should we go with the slower, more costly approach of sending up satellites, to push more back down.
Till next week,
Maxime
NASA - Astromaterials Research & Exploration Science (ARES)
https://orbitaldebris.jsc.nasa.gov/faq/#:~:text=3.-,How%20much%20orbital%20debris%20is%20currently%20in%20Earth%20orbit%3F,1%20mm%20exceeds%20100%20million.