There is more space junk in Earth’s orbit now than ever before. And this growing problem creates an increasingly dangerous environment for operating spacecraft and satellites.

Space junk consists of defunct satellites, spent rocket stages, and debris from satellite collisions and explosions.

With thousands more satellites to be launched in the coming years, the potential for collisions increases, threatening the space debris problem and creating challenges for future space activities. This problem has also given rise to a discussion of a phenomenon known as Kessler syndrome.

What is Kessler syndrome?

Kessler syndrome is a hypothetical scenario proposed by NASA scientist Donald J. Kessler in 1978 that predicts what might happen when the density of objects in low Earth orbit (LEO)—roughly 100–1,200 miles above our planet—reaches a certain critical level .

“This syndrome predicts an escalation of the space debris population, leading to an increased probability of collisions and further debris generation, resulting in a cascade of harmful effects,” wrote the authors of a 2023 study on the phenomenon, published in the journal Frontiers.

“Such collisions, even small ones, could set off a catastrophic chain reaction that would endanger all existing satellites and fill orbits with high-velocity debris. Access to orbits in space would become extremely challenging and prospects for space exploration could be jeopardized.”

Kessler syndrome is a process that can unfold over various time horizons, potentially decades to centuries, depending on factors such as the density of satellites in orbit, compliance with mitigation and debris removal efforts, and any future collisions that may occur. But such a scenario could potentially make space exploration and the use of satellites unsafe, or even infeasible—and also more expensive—for many generations.

Experts debate the potential severity and timelines of Kessler syndrome, with differing views on how quickly it could escalate and how detrimental it could be to space operations.

What technology might be at risk?

Kessler syndrome poses a significant threat to a number of technologies that rely on satellites. For example, this phenomenon could potentially result in widespread service outages affecting telecommunications and Internet services.

Navigation systems that are fundamentally dependent on the Global Positioning System (GPS) satellite would also face serious problems in such a scenario. This could impact everything from personal navigation to airline logistics. The knock-on effect would spread to other areas, such as weather forecasting, as weather satellites would be compromised.

If Kessler syndrome becomes severe enough, the phenomenon could potentially limit space exploration activities to some extent by making it difficult to launch and safely navigate a spacecraft through the debris field.

The increased risk of navigating a debris-filled orbit could jeopardize routes to the International Space Station, as well as future efforts to the Moon, Mars or more distant destinations, among others.

A growing commercial space sector, which includes satellite internet initiatives and space tourism, would face development barriers.

How can we prevent Kessler syndrome?

Measures have been put in place to try to prevent the occurrence of Kessler syndrome.

One example is the recent decision by the Federal Communications Commission (FCC) – passed in 2022 – to require satellites in LEO to de-orbit within five years of their mission, rather than the previous 25 years.

The goal of the rule, which applies to satellites licensed by the FCC or seeking access to the US market, is to reduce the amount of debris above Earth by reducing the time the objects spend in orbit.

The European Space Agency (ESA) has also reduced the maximum time spent in LEO for its new missions from 25 to five years, while NASA is reviewing its mitigation policy.

Implementation of detailed end-of-life strategies for satellites is critical, including controlled procedures for return or relocation to graveyard orbits that avoid active satellite paths.

Incorporating collision avoidance technologies and improving space situational awareness (SSA) are equally key. These efforts include more accurate tracking of space debris and the deployment of predictive systems to anticipate and avoid potential collisions in orbit. Advances in spacecraft design also aim to minimize debris generation.

At the international level, efforts such as the ESA Clean Space Initiative and the Interagency Space Debris Coordination Committee (IADC) aim to promote and facilitate global cooperation on space debris issues.

Technologies are also being developed to actively remove existing large debris from orbit using innovative solutions such as capture nets and harpoons. Other strategies include “tow sails” that speed up the process of de-orbiting spacecraft, with the ultimate goal of reducing space debris.

How many satellites has SpaceX’s Starlink launched?

Several major satellite constellation projects are underway or in the planning stages with the aim, among other things, of providing global broadband Internet coverage. There are concerns that these massive constellations increase the risk of space debris.

These projects include Starlink, a satellite Internet constellation being developed by SpaceX to provide high-speed, low-latency broadband Internet globally, particularly to serve remote and rural areas where access is unreliable or unavailable. It consists of a planned network of thousands of small satellites in LEO, working in conjunction with ground transceivers.

Starlink has launched nearly 7,000 satellites, which is the majority of the total number of satellites that are in LEO.

SpaceX has implemented several measures to mitigate the risks of space debris with its Starlink satellites, including designing the spacecraft to autonomously avoid collisions using onboard propulsion and tracking data.

In addition, Starlink satellites are placed in relatively low Earth orbit, which naturally decay over time, ensuring that they will re-enter the Earth’s atmosphere and burn up at the end of their operational life. This inherently reduces the long-term risk of debris compared to satellites in higher orbits, which remain for much longer periods.