The Kessler Syndrome is a theoretical scenario in which Earth's orbit is overpopulated with objects and debris, preventing the use of satellites in certain sections of Earth's orbit. In this scenario, space pollution is perpetuated by collisions between orbiting objects, creating more debris and thus creating a domino effect of future collisions. This theory was put forth in 1978 by NASA scientist Donald J. Kessler in a paper titled "Collision Frequency of Artificial Satellites: The Creation of a Debris Belt."
The theory has gained attention in recent years because of the growing interest in space operations among influential organizations. Several major corporations, including Amazon, SpaceX, OneWeb and Apple, reportedly plan to launch tens of thousands of artificial satellites into orbit in the coming decade. Doing so has the possibility to catalyze a scenario like the one described in Kessler's theory.
Kessler specified that the portion of Earth's orbit most at risk is low Earth orbit (LEO), but that space travel and medium Earth orbit (MEO) satellites would still be possible. However, some fear that a Kessler Syndrome scenario would completely inhibit all access to space, leaving humans and human infrastructure earthbound for several generations.
How the Kessler Syndrome works
The Kessler Syndrome applies methods used in the study of asteroid belts to predict collision patterns for active satellites in Earth's orbit.
The direct cause of a Kessler Syndrome scenario is not the existence of man-made objects themselves, but the collisions between those objects, which can generate exponentially greater amounts of debris. For example, in 2009, a collision between American and Russian communication satellites generated over 2,000 pieces of space debris. If there are more satellites, the collision frequency will likely increase.
In addition to accidental collisions, deliberate destruction of spacecraft as a result of military action also contributes to the debris count, as well as natural events like sun flares, which could cause satellites to malfunction and collide.
Each new piece of space junk also becomes a collision liability, even if the debris is much smaller than the original objects. As a point of reference, a 1-centimeter speck of paint traveling at fast enough speeds can inflict the same amount of damage as a 550-pound object traveling at 60 mph on Earth, according to NASA. Objects in low Earth orbit -- about 1,200 miles in altitude -- collide at an average speed of approximately 22,000 mph.
How likely is it to impact life on Earth?
Aside from potentially monumental effects on the environment, this scenario could lead to the serious inhibition of Earth's space programs.
The worst-case scenario in this theory would involve a runaway chain reaction of collisions between man-made objects, as well as the micrometeoroids that already exist in Earth's orbit.
A slightly less grave scenario -- but more likely -- would involve the incapacitation of most of the spacecrafts in low Earth orbit, which would significantly affect life on Earth. These satellites are the most affected by Kessler Syndrome.
Most man-made objects in Earth's orbit are LEO satellites. Many modern services rely on LEO satellites to function. These include global positioning systems (GPS) and television, as well as services used in military and scientific research. The International Space Station (ISS) and Hubble Space Telescope also sit at very low Earth orbit. Human lives would be at risk if the ISS were to collide with space junk.
NASA experts warn that the low Earth orbit is already at critical mass, meaning the addition of more objects at this point could begin an irreversible chain of collisions.
Who is launching satellites?
Despite the possibility of a Kessler Syndrome scenario, companies and governments around the world continue to plan and carry out space launches that could contribute to the overall debris count.
Recently, Elon Musk's SpaceX has requested permission to launch 42,000 satellites into space. The U.S. government approved 12,000 of these. Other large tech corporations are following suit, including Apple and Amazon, although SpaceX has the largest request so far.
These large fleets of satellites are called megaconstellations, and they are becoming more popular as satellites are becoming cheaper to build. Many companies are launching megaconstellations in preparation for the transition to 5G.
In May 2019, 60 SpaceX Starlink satellites were launched. One nearly collided with the European Space Agency's Aeolus Earth observation satellite, forcing them to move the satellite on Sept. 2 of the same year.
India's Mission Shakti -- an antisatellite missile test launched on March 27, 2019 -- also created thousands of pieces of debris.
Can Kessler Syndrome be avoided or reduced?
There is currently no protocol for removing obsolete satellites and debris from Earth's orbit.
However, close monitoring and smarter satellite designs may be able to mitigate collisions. The Space Surveillance Network is one organization tasked with monitoring the state of objects in Earth's orbit.
While NASA and the U.S. government track approximately 23,000 man-made objects softball-sized and larger, there are also countless objects too small to track in Earth's orbit; these objects can also cause destruction.
Several solar telescopes -- including the NSF's Inouye Solar Telescope and NASA's SOHO -- play an important role in monitoring potentially destructive sun flares and other space weather, which could cause satellites to malfunction and crash.
In addition to monitoring and observation, other measures can be taken to minimize collateral from satellite collisions. One is the use of a Whipple shield, which is a thin cover over the main wall of a spacecraft meant to distribute impact energy over the entire craft, lessening concentration of the blow. These shields are only effective against objects 1-centimeter wide or smaller, which is not negligible, but doesn't provide anything close to comprehensive defense.
For objects that are too big for Whipple shields, but too small to track from the ground, scientists suggest an onboard infrared camera coupled with fast-acting propellant thrusters. The camera could detect incoming debris and activate thrusters to dodge the debris, all without input from the ground. Some of these thrusters would use a special gel as a propellant that increases the number of times a satellite could use them to dodge debris.
One space contractor company is also considering a system called RUSTLER (Round Up Space Trash for Low Earth orbit Remediation), which would be a midsize vehicle designed to gather and dispose of debris. The crafts would send pulses to space junk through electrodynamic tethers. The pulse would interact with Earth's gravitational field, creating an atmospheric drag effect that lowers the debris into Earth's atmosphere, where ideally it would burn up in its descent.