One morning in June 2022, two colossal pieces of space history — once proud symbols of Cold War ambition — came perilously close to a cataclysmic collision in Earth’s orbit. On one side was a spent Soviet Zenit rocket, an eerie relic of a bygone era. On the other, a derelict American booster, similarly abandoned after delivering its payload to space decades ago.

The two hulking objects drifted through low Earth orbit (LEO) at speeds that defy comprehension — tens of thousands of kilometers per hour — closing the vast distance between them in mere seconds. If they had collided, the impact would have produced a lethal spray of debris that could have imperiled satellites, space stations, and astronauts for generations.

That near-miss was just one example of the growing problem of space debris, a problem that is quickly spiraling into a crisis.

Space Junk

The Cold War may have ended, but the junk from that era — and from every subsequent space mission — is still up there, circling Earth in a chaotic, ever-growing cloud of debris. Scientists now refer to this as space junk. Abandoned rocket stages, broken satellites, and shards of exploded spacecraft continue to pose a deadly threat to both space exploration and the satellites that support our modern world.

Space junk is an invisible menace, one we seldom think about as we marvel at the satellites beaming down our GPS signals or track the progress of astronauts aboard the International Space Station (ISS). Some debris is as big as a school bus, and some is no larger than a paint chip. But this debris is moving at speeds that make even the smallest object deadly. And as more and more satellites are launched into orbit, the problem grows exponentially.

What was once a manageable concern has become what experts in the field refer to as a “ticking time bomb”. It now threatens not just individual spacecraft, but the future of space exploration itself.

A Growing Minefield in Earth’s Low Orbit

The amount of debris in low Earth orbit is staggering. According to the European Space Agency (ESA), more than 170 million pieces of space junk are currently orbiting Earth. This debris ranges in size from minuscule fragments to massive objects like derelict satellites and rocket boosters. Each is potentially catastrophic if it collides with a functioning spacecraft. And they could be deadly if they hit the International Space Station or any manned spacecraft.

Darren McKnight, a Senior Technical Fellow at LeoLabs, a firm that specializes in tracking space debris, has been ringing the alarm for years. “This is a ticking time bomb,” McKnight said in an interview with Forbes. “This grim reality means that collisions are not a question of if but when.”

McKnight and his team at LeoLabs have spent years developing tools to monitor and predict these collisions. Their network of radars tracks more than 20,000 objects in low Earth orbit, offering satellite operators advanced warnings of potential collisions. Yet for all the advancements in tracking, the situation remains precarious.

LeoLabs’ network can only track objects larger than 10 centimeters. Tens of thousands of smaller pieces of debris — each capable of destroying a spacecraft or satellite — remain invisible to their radar systems. These unseen fragments, the residue of previous explosions and collisions, continue to spread across the orbital plane. Though tiny, these fragments whip around the Earth at stupendous, deadly speeds. Any collision will release a high amount of kinetic energy.

Deadly Ghosts of the Past

In recent years, the ISS has been forced to make multiple collision avoidance maneuvers to dodge incoming debris. Each time, mission control has to carefully calculate the station’s movements, sometimes with only hours to spare. A single fragment, just a few centimeters wide, could be lethal to astronauts spacewalking outside the station. Even a millimeter-sized piece can tear through spacecraft with the force of a bullet, as was demonstrated when a small shard of debris ripped a 5-millimeter hole in the ISS’s robotic arm in 2021.

McKnight is quick to point out though that the most immediate threats come not from the tiniest fragments, but from larger, derelict objects that continue to drift through space, uncontrolled.

These ghost rocket stages are stalking the higher reaches of low Earth orbit, the scientist says, pointing to old upper-stage booster rockets abandoned by the United States, Russia, and China, among others. Some of these rockets have been in orbit for decades, and like many defunct satellites, will continue to circle the Earth for centuries before they are naturally dragged down into the atmosphere by Earth’s gravity.

In the 1960s and 70s, during the height of the Space Race, the superpowers routinely discarded their spent rocket stages in orbit, with little concern for the future. No one envisioned that these once-vital machines would become lethal obstacles to future missions. Today, McKnight says, they are among the top 50 most dangerous objects in space.

The threat from these ghost rockets is so severe that McKnight has teamed up with Ian Christensen, a senior director at the Secure World Foundation, to push for international cooperation on active debris removal. Their argument is simple: spacefaring nations must start cleaning up their own mess, or risk losing access to low Earth orbit entirely.

The two have helped stage a space summit in New Zealand in early 2024 where they managed to gather many space scientists and industry experts to tackle the issue. However, they didn’t make much headroom and found that most space experts had raised this serious issue to relevant bodies, governmental or otherwise, but little had been done. They lamented that “only a major debris-generating collision would stimulate true international resolve and commitment for debris remediation missions,” Christensen told Forbes.

The Kessler Syndrome: A Cascade of Collisions

The scenario McKnight and other experts fear most is known as the Kessler Syndrome, a hypothetical but increasingly plausible scenario where a single collision triggers a cascade of further collisions, each generating more debris, until Earth’s orbit becomes an impenetrable minefield. The idea was first proposed by NASA scientist Donald Kessler in 1978, and while it once seemed like a far-off possibility, the growing density of debris in low Earth orbit has made it a very real threat.

In 2009, a vivid illustration of this danger unfolded when two satellites, an active U.S. communication satellite called Iridium-33 and an inactive Russian military satellite, Cosmos-2251, collided at nearly 42,000 kilometers per hour. The impact shattered them, creating more than 2,000 pieces of trackable debris, along with tens of thousands of smaller, untrackable fragments. The collision was the first of its kind, a crash between two intact satellites. But it likely won’t be the last.

In 2023, a near-miss occurred between two defunct satellites, the U.S.-U.K. IRAS space telescope and the Russian Cosmos-2221. The two objects passed within just 10 meters of each other, a dangerously close call. Had they collided, experts estimate the crash would have generated between 2,000 and 7,000 fragments, each large enough to be tracked from Earth (with many more fragments untrackable). The implications of such a collision would have rippled far beyond the initial impact, potentially igniting a Kessler-like cascade.

Even small collisions can have outsized consequences. In 2016, a 1-millimeter piece of debris struck a solar panel on the Copernicus Sentinel-1A satellite, temporarily reducing its power. The satellite survived the impact, but the incident served as a stark reminder of how fragile our space infrastructure really is. In a more severe scenario, such an impact could easily disable a critical satellite, cutting off access to essential services like GPS, telecommunications, or climate monitoring data.

It’s Getting Crowded Up There

Since the launch of Sputnik 1 in 1957, satellites have become an integral part of modern life. Today, they power everything from cellular networks to weather forecasts, from military communications to environmental monitoring. But as the number of satellites in orbit increases, so too does the risk of collisions.

The recent explosion in satellite launches is driven in large part by companies like SpaceX, whose Starlink constellation aims to provide global internet coverage through a vast network of low Earth orbit satellites. Since 2019, SpaceX has launched more than 7,000 Starlink satellites, with plans to deploy thousands more in the coming years.

While these satellites are equipped with onboard propulsion systems to avoid collisions, the sheer number of objects in orbit is overwhelming.

In the first half of 2024 alone, Starlink satellites performed nearly 50,000 collision-avoidance maneuvers. This staggering number reflects both the density of objects in orbit and the increasing reliance on automated systems to manage collision risks. But some experts worry that as the number of satellites continues to grow, these systems may not be able to keep up. At some point, avoidance maneuvers wouldn’t be possible in an ever-crowded low orbit, making collision imminent.

Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, has voiced concern that “we are operating at the edge of what is safe.” If one of these systems fails, it could set off a chain reaction that would be difficult—if not impossible—to stop.

And it’s not just low Earth orbit that’s at risk. In 2024, a piece of discarded cargo from the ISS re-entered Earth’s atmosphere and crashed through the roof of a house in Florida. The debris was part of a supply pallet that should have burned up upon re-entry, but a 1.6-pound chunk survived, punching through both the upper and lower floors of the home. Luckily, no one was hurt, but the incident underscores the growing risks posed by space junk, not just to satellites and astronauts, but to people on the ground as well.

What To Do to Clean Up Space?

The question, then, is what can be done about all this debris? The first step, according to experts like McKnight and Christensen, is international cooperation. “The biggest diplomatic challenge is convincing the three major spacefaring countries — the United States, Russia, and China — who are responsible for 90% of the risk, to begin remediating their own large debris objects,” Christensen says.

The most basic approach to managing the space junk problem is first and foremost prevention: designing missions and satellites so that no additional space debris is generated in the future. For instance, space agencies like NASA and the European Space Agency (ESA) have introduced strict guidelines for new satellite launches. These guidelines require operators to remove their spacecraft from orbit at the end of their operational lives, either by forcing them to re-enter Earth’s atmosphere — where they burn up — or by sending them into so-called “graveyard orbits” far from vital satellite paths.

In the U.S., the Federal Communications Commission (FCC) passed a rule in 2022 requiring satellite operators to deorbit defunct satellites within five years of completing their mission, significantly shortening the previous guideline of 25 years. This is seen as an important step toward slowing the accumulation of space debris, but it only applies to newly launched satellites. The millions of fragments and dead satellites already in orbit remain a persistent threat.

Efforts to address the space debris crisis in the United States gained momentum with the introduction of the ORBITS Act, a bill designed to jumpstart active debris removal (ADR) missions. The Act proposes a $150 million fund to support the development and demonstration of technologies aimed at cleaning up the most dangerous objects in orbit, like defunct satellites and abandoned rocket stages. The bill has never been voted on in the House of Representatives, but scientists like Christensen and McKnight are lobbying hard for it.

Space Junk Collectors

ADR technology is still in its infancy but there is progress. In 2024, the Japanese firm Astroscale received a $80 million contract from the Japan Aerospace Exploration Agency (JAXA) to remove the upper stage of the JAXA’s H-IIA rocket from orbit using a newly developed satellite equipped with a robotic claw. The company envisions launching a fleet of “space janitors” that can attach themselves to defunct satellites or other debris and guide them to re-entry, where they’ll burn up in the atmosphere. Earlier in 2014, Astroscale demonstrated its capabilities by placing one of its satellites just 50 meters (164 feet) away from the upper stage of the H-IIA rocket.

In Europe, the ESA is pursuing similar goals with its ClearSpace-1 mission, scheduled for launch in 2026. The mission plans to deploy a spacecraft to capture and deorbit a large piece of debris using a multi-armed robot.

Some researchers are investigating the use of ground-based lasers to “nudge” debris into lower orbits, causing it to burn up in the atmosphere before it can collide with a satellite. The idea, known as “just-in-time collision avoidance,” involves firing short pulses of laser light at debris, providing a gentle push to alter its orbit.

Other efforts are even experimenting with the idea of using nets and harpoons to catch larger debris objects. So both a space janitor and a “space fisherman”.

As the space economy continues to grow, projected to exceed $1 trillion by 2040, the pressure to find solutions to the space junk problem will only intensify. The stakes are high. A single catastrophic collision could destroy vital communication networks or put astronauts’ lives in danger. And with thousands of new satellites slated to launch in the coming years, the margin for error is shrinking.