There was nothing terribly remarkable about the Iridium 33 and Kosmos 2251 satellites—at least not at first. Iridium was a 1,500 lb. communications satellite the U.S. launched into space in 1997; Kosmos, was another communications satellite, also tipping the scales at 1,500 lb., that Russia sent aloft in 1993. 

That’s a lot of metal moving with a lot of speed—17,500 miles per hour—and it paid for ground controllers to keep the ships flying true. When it came to Iridium, that was relatively easy, with occasional thruster tweaks holding the satellite upright and moving it out of harm’s way. Kosmos was a different matter.

Just two years after its launch, in 1995, the satellite failed, becoming nothing more than space junk, tumbling uselessly through its orbit. On Feb. 10, 2009, the dead bird and the live bird crossed paths and collided, resulting in an explosion of metal, silicon, wire, plastic, tanks, fuel, and more. The loss of the defunct Kosmos meant nothing to the Russians. The loss of the living Iridium left a hole in the American space communications web. But far more important were the conditions in space—at the site of the collision.

What is the Kessler syndrome and is it possible?

The cosmic crackup between the two ships left behind more than 1,800 pieces of debris at least 10 cm (4 in.) or larger. That’s a huge problem, since even such small bits of scrap can carry the bang of a bullet when they’re traveling at orbital speed. Should one or more of them strike one or more other satellites—or, much worse, a crewed spacecraft—they could destroy that object, creating more debris clouds, which would strike still more spacecraft, leading to a chain reaction known as the Kessler syndrome that could potentially wipe out whole flocks of spacecraft in that orbital band.

“The Iridium-Kosmos collision… created significant amounts of debris in highly populated orbits,” says Chris Blackerby, chief operating officer of Astroscale Holdings, a Japan-based company that focuses on satellite servicing, inspection, and life extension, and removing debris from low-Earth orbit. “It's not like one accident is necessarily going to have an immediate, massive impact on our entire utilization of LEO [low-Earth orbit]. But it's incremental; the more we don't pay attention to it, the more it's going to be a massive problem for generations down the line.”

How many satellites are there and how much space debris exists?

“Massive” is by no means too strong a word for the mess in near-Earth space. According to NASA’s Orbital Debris Program Office, more than 25,000 objects larger than 10 cm are currently orbiting Earth, most of them satellites—either active or no longer operating. But that’s only a tiny fraction of the problem. There are 500,000 objects measuring 1 to 10 cm, and 100 million in the 1-mm range.

The crowding in space is growing exponentially worse with the boom in satellite constellations. SpaceX’s Starlink constellation now numbers 9,400 satellites—or 63% of the 14,900 active satellites orbiting Earth. As TIME reported in March, SpaceX is seeking to more than double the size of its fleet, upping the starlink numbers to 20,000. And that’s nothing compared to a head-spinning proposal the company made in a January filing with the Federal Communication Commission (FCC) mission to launch a full million AI satellites. Meanwhile, on March 19, Blue Origin, the rocket company founded by Amazon boss Jeff Bezos, filed a request with the FCC to launch an AI constellation consisting of up to 51,600 satellites.

Already, satellite developers are feeling the pinch of the problem and, like drivers planning a long road trip, are avoiding the most overcrowded highways. NASA defines three main orbital altitudes: low-Earth orbit, which extends from 111 mi. to 1,242 mi. up; mid-Earth orbit, from 1,242 mi. to 22,231 mi.; and high or geosynchronous orbit, above 22,231 mi. 

According to Luc Piguet, CEO and a co-founder of ClearSpace, a Luxembourg-based company that specializes in safe removal of dead or dying satellites, “If you take [orbits] between 800 km and 1,000 km (500 mi. to 620 mi.), these are typically orbits where operators don’t launch constellations anymore because it’s too risky.” 

Humanity is heedless of all the clutter in those bands. Last year, there were 315 successful orbital launches worldwide, with SpaceX alone accounting for more than half, at 165. Since its first launch in 2010, the company’s workhorse Falcon 9 rocket has flown successfully 624 times; many of those flights have lofted up to 60 Starlink satellites at once.

“The number of objects in low Earth orbit has grown ten-fold in the last 10 to 15 years,” says Blackerby. “When Astroscale started in 2013, there were about 1,000 satellites in LEO. Now there’s roughly 15,000.”

Is it safe to have so many satellites in space?

Astronomers and other scientists are sounding an alarm bell, but as with climate change and the $38.9 trillion national debt, we’re putting off the problem until sometime in the undefined future. Depending how high satellites are flying, it can take years, decades, or even centuries for their orbits to decay to the point that they drop into the atmosphere and disintegrate on their own. Orbital debris is a problem that began in the 20th century, has grown worse in the 21st, and may not be resolved till the 25th, 26th, or beyond.

“Is it an immediate existential problem now?” asks Blackerby. “Probably not. But is it something that is building to be a problem in the future? Undoubtedly yes. It is unlikely that there is going to be a massive, massive accident tomorrow that causes a Kessler syndrome event. But this is a long-tail problem.”

Just how vulnerable a functioning satellite or spacecraft is to space debris depends on just where the object is orbiting. Far and away, it’s the low band that presents the greatest worries, with 24,185 large objects spinning around the planet. Among the most vital and prized of the objects in that band are the International Space Station (ISS), the Hubble Space Telescope, and China’s Tiangong space station.

The ISS takes a pounding from flying so low. Spacewalking astronauts routinely observe pockmarks in the sides of the station, as if it had been hit by buck shot—the result of impact with small debris particles. To combat this, the station is covered with 100 so-called Whipple shields—a sort of external armor that does not stop micro particles from hitting the station, but breaks them up into smaller particles before they penetrate the shields. Still, on average, ISS astronauts have to maneuver the station to avoid an incoming debris hit at least once a year. If maneuvering isn’t sufficient, they will also shelter in place in the Dragon and Soyuz spacecraft attached to the station, allowing them to cast off fast in the event of a destructive hit.

“Once a year doesn’t sound like a lot,” says John Crassidis, a distinguished professor of aerospace engineering at the University at Buffalo, “but it actually is a lot.”

Moving the station to a higher, more sparsely populated orbit is not an option. Its current, 250-mi.-high orbit was first determined by the flight characteristics of the space shuttle, which performed most of the ISS assembly and was limited by its rocket and thruster power to fly in a low-orbit band from 115 miles to 400 miles. Similar altitude limits on the station’s cargo and crew transfer vehicles keep the ISS stuck where it is. Hubble, similarly, flew low so that the shuttle could get to it for repair missions.

Things get even more more dangerous for LEO satellites when they fly not circular orbits, but egg-shaped or elliptical ones. Elliptical orbits are often used for scientific missions when researchers want to observe the Earth from different altitudes or fly into and out of radiation belts to sample their energy at different distances. But that carries risks. 

How do we prevent satellites from colliding?

One of the reasons collisions in space don’t happen all the time is that every spacecraft in a certain fixed orbit—say, a circular one 200 miles up—is flying in the same direction at the same speed. It’s a bit like hundreds of cars on a crowded highway all moving at 65 mph. As long as that speed doesn’t change, the distance between the cars neither grows nor shrinks. Elliptically flying spacecraft, however, have to cross over the circular orbits as their altitude increases or decreases—a bit like one of those cars cutting across four lanes of traffic—and that can spell trouble.

“If you're not on circular orbits, but on eccentric ones, you have large differences in relative velocities,” says Carolin Frueh, associate professor of aeronautics and astronautics at Purdue University. 

If satellite constellations are exacerbating space traffic, their developers are doing what they can to mitigate the problem. One way is by launching into so-called shells. Rather than firing a thousand satellites into an orbit of, say, 300 miles, companies will put some of them 270 miles up, others at 290 miles, others at 310 miles and elsewhere. As on Earth, a few new highways will always reduce the traffic on an existing one.

“A million [Starlink] satellites is a lot,” concedes Gwynne Shotwell, president and chief operating officer of SpaceX, of the company’s planned AI constellation. “We will do what's necessary to be safe. There'll be many shells of these AI satellites.” 

What Shotwell sees as the bigger problem is not the relatively easy business of parceling satellites out into shells, but getting the owners and operators of the spacecraft in each shell to communicate with one another about any maneuvers they may be planning to make. “The problem with space traffic control is when companies or countries don't tell us where the satellites are going to be,” she says. “You really need to share your ephemeris. If you're going to do a maneuver, please let us know so that we can make sure we get out of your way.”

Satellites could also benefit from automating collision avoidance. Most operators of constellations or individual satellites monitor their spacecraft from the ground and direct them manually to fire their thrusters and adjust their position when a collision threatens. SpaceX’s Starlink satellites are equipped with on-board systems that operate on their own, dancing the satellite this way or that to steer clear of nearby traffic. The company takes collision risk seriously and adjusts any Starlink’s position when the danger of impact is as little as three in 10 million. In a late December document filed with the FCC, SpaceX reported that it had performed about 300,000 Starlink maneuvers in 2025 alone.

“Give credit to Starlink,” says Blackerby. “They do have automated collision maneuvers built into all of their satellites, so they're automatically avoiding each other and other objects in their orbit as they're operating. There's step one that's a good start on the prevention side.”

Another step could be national or international regulation of where satellites can be deployed. If there’s a wild west quality to the doings in low-Earth orbit, things get a lot more orderly the higher up you go. Most satellites, orbiting at a few hundred miles up, require about 90 minutes to make one circuit around the Earth. With every additional mile of altitude, however, the spacecraft inscribe a larger circle—one that takes longer to complete. At an altitude of just over 22,000 miles, that circle is so big it actually matches the rotation of the Earth, taking 24 hours for one revolution. The result is that the spacecraft effectively hovers over a fixed point on the ground below, tracking it through its daily spin. Such so-called geostationary orbits are especially valuable for communications and surveillance satellites that need to serve—or spy on—particular terrestrial locations. Currently there are about 575 satellites in geostationary orbit, marking their steady daily path around the world.

Since all geostationary satellites are in the same orbit, there are a limited number of slots available for each of them to fly safely. The International Telecommunications Union, a United Nations-sponsored organization made up of 194 countries and 1,000 telecom companies, assigns those slots to countries, which then assign them further to local companies in the launch business. 

“It’s a little bit like the way radio frequencies are assigned,” says Piguet, of ClearSpace. “The number of geostationary satellites we launch is much lower than what’s in LEO.”

What happens to a satellite when it dies?

Not only are there fewer satellites up at the nose-bleed altitudes, they are easier to handle when their useful life ends. Rather than drifting aimlessly through traffic made up of live, functioning satellites, dead geostationary satellites are boosted a few hundred miles up to what are known as graveyard orbits, where they can circle the Earth for millennia, entirely harmlessly.

“That’s one of the rules we put on our companies and our sister nations,” says Crassidis. “Those [satellites] are never coming down.”

In LEO, orbits decay much faster. Even hundreds of miles above the Earth, trace wisps of high atmosphere exert a subtle drag on orbiting objects, slowly decelerating them and eventually pulling them down out of the sky. On their downward tumble they cross lower lanes of orbital traffic and pose an uncontrolled collision risk.

To reduce the danger, the FCC had a longstanding 25-year rule, requiring any new satellite to have an end of life plan, with operators bringing it down in a controlled fashion within 25 years of the time its service stops. In 2022, that rule was tightened to just five years. That’s a solution—but only a partial one.

“I think that that is very important,” says Frueh. “But I don't think that solves all the problems, because you still have to go through the lower shells of the other orbits.”

Just how controllers pull a dead or dying satellite out of orbit is another matter. Spacecraft that still have maneuvering fuel in their tanks can simply fire their engine or thrusters, slow their speed, and make the same kind of controlled reentry crewed spacecraft make. Other simple technologies are being developed in which satellites inflate a balloon, unfurl a sail, or deploy long straps that increase atmospheric drag and speed their reentry. More elaborate technologies are being developed as well.

Astroscale is working on a system in which satellites are equipped with magnetic plates allowing them to be captured by disposal satellites which carry them down to the upper atmosphere and dump them for an incinerating descent. ClearSpace is doing similar work that would allow satellites to be grappled with a tentacle array.  And it’s not just disposal services that the companies could provide. ClearSpace is also working on plans to service existing but aging satellites so that they can stabilize their orbits and avoid becoming drifting space junk 

“There’s many other services, like inspection, life-extension, refueling, repair, or other intervention,” Piguet says. “It’s not too late to introduce servicing into this ecosystem.”

Ultimately, trash in space is very much like trash on Earth—the result of a too-often careless species that makes a mess of its environment with little regard to the consequences. When it comes to low-Earth orbit, those consequences are coming due. 

“Space is big,” says Crassidis, “but it’s getting smaller every day.”