Kessler Syndrome and Space Exploration

Every day it becomes easier and cheaper to place an object into orbit. This is great for science and communications, but if we are not careful enough with the way we handle these gadgets once they have finished their mission, we could turn low Earth orbit into a true unusable space graveyard. This problem has been analyzed in depth by NASA consultant Donald J. Kessler.

We are in an era where anyone (as long as they have a few euros on hand) will be able to put their own satellite into orbit. With TubeSat, for example, everything is fine, because when it stops working (after a few weeks) it disintegrates in the atmosphere. But if this kind of initiative keeps thriving, the consequences could be dire for the future of our space race.

As the number of objects orbiting the planet increases, so does space debris and the chances that one of those pieces of junk will end up colliding with a device still in service. This scenario has been thoroughly analyzed by NASA consultant Donald J. Kessler, after whom the problem has been named Kessler Syndrome.

The Kessler Syndrome

According to Kessler, at some point in the near future, the volume of space debris in low Earth orbit will be so high that objects in orbit will have a high probability of being impacted by debris. This process will create even more junk, which in turn will increase the risk of other satellites being impacted, creating a harmful vicious cycle. As the number of satellites in orbit grows and they become old, the probability of suffering Kessler Syndrome increases, since most “retired” satellites do not have fuel that would allow them to “move” out of the way if threatened by a piece of junk.

What makes Kessler Syndrome so dangerous is the “domino effect”, since impacts between two objects of significant mass will create a lot of additional debris as a result of the collision. Each piece of shrapnel has the potential to cause damage to other objects in orbit, which in turn creates more space debris. If a collision were large enough—between the space station and a satellite, for example—the amount of debris generated could be high enough to make low Earth orbit unusable.

Space debris travels at speeds too high to try to collect it. Furthermore, its large number and small size make it unfeasible to design specific missions to remove it from orbit. Of course, all these objects will, at some point, succumb to air resistance in the extremely thin upper atmosphere and burn up during reentry, but it is a very slow process that will take hundreds (or thousands) of years. Some ferrous metal pieces that can interact with Earth's magnetic field will fall first, within a few decades.

Space agencies know this problem well, and design missions taking into account everything necessary so that objects sent into space do not end up damaging other vehicles. For example, satellites can be safely disposed of at the end of their useful life, either by means of a controlled reentry into the atmosphere (in the case of low orbits) or by sending them to a “graveyard orbit” if they are “geostationary”. We know that atmospheric friction keeps the lowest orbits clean.

Everything that rotates at less than 500 kilometers in altitude and does not have fuel to make corrections will be swept away in a few months. But the high orbits, where communications satellites are located, do not have this natural “cleaning assistant”.