Kessler Syndrome: The Space Debris Domino Effect

Since the beginning of the Space Race in the 1950s, countless satellites have been launched into Earth’s orbit with over 10,000 satellites currently reported in orbit by the UN. However, satellites don’t last forever due to mechanical components wearing down or electronics degrading. As a result, unused satellites or pieces of satellites can become space debris—uncontrolled, human-made objects floating around in orbit. Spacecraft collisions with these debris can be extremely hazardous, regardless of the size of the debris, due to the high speed of objects in orbit and sensitivity of the equipment. The hypothetical and catastrophic domino effect that describes the chain reaction of impacted spacecraft becoming space debris and hitting other spacecraft is known as Kessler syndrome.

In 1978, while conducting research on debris from explosions in Earth’s orbit, NASA scientist Robert Kessler conceived a chilling possibility that there was a positive correlation between the number of satellites in space and the number of collisions between satellites and space debris. This meant collisions would increase in number as more and more satellites were launched. Additionally, he figured that as satellites collide with space debris, the satellite most likely ejects debris of its own, which in turn causes more collisions. He eventually reached a theory where an exponential increase in space debris would reach the point where Earth’s atmosphere would be filled with enough space debris to make launching new spacecraft nearly impossible, as anything entering orbit would quickly be annihilated by this debris. In his research paper, Kessler noted that this chain reaction wouldn't be a single, apocalyptic event happening in the span of a few days or weeks and instead would accumulate within a few decades. Fellow scientists like North American Aerospace Defense Command’s John Gabbard took note of Kessler's work—Gabbard himself coining the term “Kessler syndrome.”

In his 1978 paper, Kessler created a mathematical model of collision probabilities, predicting that Kessler syndrome would become a significant possibility by 2000 if launches of spacecraft continued at the same rate as they had in previous decades. Fortunately, Kessler’s original prediction hasn’t quite materialized yet, but space debris has already proven itself to be a threat. In 2009, a particularly severe incident involving a collision between a communication satellite and an unused satellite produced over 2,000 pieces of debris. In the summer of 2023, an Earth-based radar detected a similarly destructive collision between space debris and yet another unused satellite, which served as a stark reminder of the consequences of ignoring the threat of space debris. 

Despite the evident risk presented by increased launches of spacecraft in an environment already thoroughly populated with satellites, the number of spacecraft launches every year has only gone up, with 2023’s record 180 launches. Additionally, many agencies and nations are planning large-scale launches of satellite networks known as satellite constellations. Constellations can consist of hundreds or even thousands of individual satellites with constellations like Elon Musk’s Starlink system currently consisting of over 5,000. Due to the sheer number of satellites in one of these constellations, the risk of collisions is significantly higher than that of just one satellite. Additionally, a number of anti-satellite weapons have been developed by nations around the world. Among these weapons are missiles designed to hit and destroy satellites in orbit, creating yet another unregulated source of space debris. In fact, global militaries have destroyed five satellites during weapons tests since 2000 and have created over 5,000 pieces of debris.  

A chain reaction described by Kessler syndrome happening in the modern day would have massive consequences back on Earth’s surface. Not being able to launch satellites would greatly hinder all industries involving satellite use. The destruction of satellites providing navigation services, for instance, would have far-reaching effects from hindering transportation across large distances to limiting the functionality of smartphone maps. A lack of communications satellites could cause a global communications blackout, which would impact nearly every aspect of modern life from a basic phone call to global politics and economics. Additionally, a cataclysmic space debris event would make space launches and exploration all but impossible, and any satellites or other spacecraft trying to enter orbit after one of these events would almost certainly be destroyed by pieces of debris. 

Currently, there are no international initiatives to clear Earth’s orbit of debris and defunct satellites. However, smaller actions have been taken by individual organizations in the fight against space debris. For instance, the Federal Communications Commission’s five-year rule entails that after a satellite orbits for five years, its operators must remove it from orbit by maneuvering it to an altitude low enough for it to safely fall to Earth. Additionally, monitoring larger pieces of space debris can help satellites avoid collisions. The U.S. Space Surveillance Network tracks space debris greater than 10 cm, and ground-based radar systems can track debris as small as 3 mm. Furthermore, there has been an effort to remove orbital, man-made objects. Debris can be removed through active debris removal, the process of physically capturing and deorbiting defunct satellites using robotic arms, nets, or lasers. However, active debris removal technologies remain in their early developmental stages. Research into these technologies is ongoing, such as the European Space Agency’s planned ClearSpace-1 program’s robotic claw to capture pieces of debris and the promising Japanese startup Astroscale’s satellites, designed to magnetically dock with pieces of debris and maneuver them accordingly. 

The growing risks of Kessler syndrome and space debris will continue to pose a threat to spacecraft. Addressing this issue will be critical to expand humanity’s presence in space and ensure the continued use of satellites for critical purposes like communication and navigation. Establishing clear regulations is crucial to minimizing the creation of more space debris from new launches and weapons systems. Fostering greater global collaboration for monitoring space debris and developing new technology will be necessary for creating a safe and effective solution to Kessler syndrome.