What Is Space Junk, and What Can Be Done About It?

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According to the European Space Agency (ESA), more than 170 million pieces of space junk are currently orbiting Earth. But what is that debris exactly, and how did it get there? Is the accumulation of space junk even a problem? If so, are we able to clean it up? Read on to get the answers to these questions (and others) in ExtremeTech’s scoop on space junk.

What Is Space Junk Made Of?

When experts use the term “space debris,” they’re referring to pieces of human-made material that were once used for space exploration and left in orbit. Instead of re-entering Earth’s atmosphere and burning into smithereens, that material languishes in space, waiting for a convenient bump toward Earth or a space junk retrieval mission. Though asteroids might produce debris when they collide with other natural space bodies, space junk almost always points to stuff that wouldn’t have ended up in space without human interference.

We humans love exerting our influence whenever and wherever we can, and space is no exception. It follows that the trash we’ve launched into or left in space varies widely. Here are a few of the most common (and problematic) types of space debris.

Retired or Dysfunctional Satellites

Every mission has an expiration date. If all goes according to plan, that date arrives when the mission has run its course and the relevant space equipment has run out of fuel. Other times, the mission is forced to end prematurely, whether for mundane reasons (like the ESA’s loss of communication with Envisat in 2012) or catastrophic failure (like the 1986 Challenger explosion). If a piece of equipment becomes derelict after having exited Earth’s atmosphere and settled into orbit, the odds are higher that it will remain in orbit—and without a whole lot of atmospheric drag, a retired satellite can continue orbiting Earth for a very long time. 

Vanguard-1 superimposed over an image of space.
Credit: Hydrargyrum/National Space Science Data Center/

Take Vanguard-1, a shiny metal ball the US Navy launched in 1958 to respond to the Soviet Union’s Sputnik and Sputnik 2. The first satellite powered by solar cells, Vanguard-1 offered early data on Earth’s shape and atmospheric density until the Vanguard mission ended in 1964. More than 70 years later, Vanguard-1 continues to orbit Earth and holds the record for remaining in space longer than any other human-made object. Experts estimate that the retro satellite won’t re-enter Earth’s atmosphere for at least a couple hundred years.

It’s hard to imagine such an endearing piece of space history as junk, but satellites long past their retirement dates make up a significant portion of human-made space debris. Of the roughly 29,000 pieces of space debris larger than 10 centimeters (3.9 inches) currently circling Earth, most are satellites or satellite-adjacent. Vanguard-2—Vanguard-1’s sister satellite—stuck around after its days-long mission was over; it’s expected to remain in space for 300 years. Canada’s first satellite, Alouette 1, has spent more than five decades in orbit despite its retirement in the 1970s. 

Modern satellites also continue to orbit Earth post-retirement: After the Kepler Space Telescope ran out of fuel in 2018, NASA ended the mission and left the spacecraft in orbit, while the National Oceanic and Atmospheric Administration’s NOAA-19 continues to trot around Earth despite its mission’s demise in 2016. 

Rocket Stages

Also contributing significantly to the growing space junk problem are spent rocket stages. The ESA estimates that 11% of cataloged space debris are upper stages, which are vital to launching satellites and other spacecraft into orbit. Once these rocket parts have completed the job, they often remain in low-Earth orbit (LEO), medium-Earth orbit (MEO) or geostationary orbit (GEO), depending on the mission in which they were involved.

As with satellites, the upper stages floating around space vary a good deal, from pieces of SpaceX’s Falcon 9 to stages from Soviet-era Proton rockets.

Artist’s depiction of a rocket body exploding in space.
Credit: ESA

Fragmentation Debris

It’s simple: The more stuff there is orbiting Earth, the higher the likelihood that some of that stuff will collide with other things. In 2009, a privately owned American communication satellite, Iridium-33, smashed into a Russian military satellite, Kosmos2251, at 7.3 miles per second. It was the first known in-orbit collision to occur between two human-made spacecraft, but certainly not the last: In 2023, the ESA found that space debris tends to smash into other debris, producing fragments of trash that would also be doomed to float in space for decades or longer. 

Fragmentation debris can also result from satellite and rocket body explosions in orbit. Typically, this happens because a spacecraft’s tank or fuel line contains residual fuel, which ignites in the spacecraft’s harsh environment following a bit of decay. These explosions add to the 170 million pieces of 1-millimeter debris currently floating in space. This means that while the overall mass of our celestial neighborhood’s litter might remain the same, it’s more spread out, and collisions are bound to continue if humans don’t intervene.

Human Waste

Human waste admittedly makes up a very small portion of space debris, but we’d be remiss not to include it. Astronauts don’t get to put their normal bodily functions on hold just because they’re achieving the once-unimaginable, and all that fecal matter has to go somewhere. Some of it has sat in bags on the Moon for around half a century, thanks to Apollo 11’s astronauts and the moonwalkers who came after them. Other human waste parcels are expelled from the International Space Station (ISS), after which they burn upon re-entry into Earth’s atmosphere—if everything goes the way it should. 

What’s So Bad About the Accumulation of Space Debris?

So, space junk begets more space junk. But why should we care? After all, if it’s stuck up there and we’re down here, why is space debris our problem?

To start, every potential collision between an operational spacecraft and space debris increases that spacecraft’s risk of malfunctioning. This became clear in 2016, when a 1-millimeter piece of debris hit a solar panel on the Copernicus Sentinel-1A satellite. While the satellite survived the impact—the Copernicus team observed a small but temporary reduction in power—space agencies could ignore it no longer: Space junk poses an active threat to ongoing and future space missions. 

Debris can interrupt human activity in space, too. This summer, astronauts aboard the ISS were forced to shelter in various docked spacecraft after Russia’s defunct Resurs P1 satellite broke into a cloud of dangerous fragments. It wasn’t the first time the ISS crew had to shelter in place; thanks to decaying satellites, astronauts and cosmonauts have had to hide out in docked spacecraft roughly once every two years since 2009.

The ISS debris that crashed through a Florida resident’s roof in 2024.
Credit: Alejandro Otero via X

Also, space junk doesn’t always stay in space. In April 2024, a piece of debris from the ISS fell through Earth’s atmosphere and smashed through the roof of a Florida resident’s house, plus his upper and lower floors. The supply pallet from which the debris had come was supposed to have burned away upon re-entry into Earth’s atmosphere, but a 1.6-pound chunk of metal survived. While the homeowner and his son were unharmed, the damage to the home had to have been costly, and the in-progress legal process that followed will determine the extent to which space agencies are responsible for space junk’s impact on everyday citizens. 

Roof-destroying pieces of space junk might not fall from the sky very frequently, but it’s in space agencies’ and private space companies’ best interest to prevent similar incidents from happening in the future. One way to do that, of course, is to ensure that debris headed for Earth’s atmosphere is actually aerosolized upon re-entry. But reducing the amount of junk we jettison into space—or changing that junk’s makeup—will also shrink the regularity with which re-entry issues occur.

How Can We Clean Up Space Junk?

After a tiny fleck of debris hit Sentinel-1A, the ESA announced that it was time to get serious about removing and preventing the accumulation of space junk. Space agencies began to toy with the idea of requiring organizations to deorbit their retired satellites; while NASA suggested at the time that derelict satellites deorbit after 25 years of retirement, there were no penalties for organizations that didn’t follow its guidance. 

In 2022, the United States Federal Communications Commission (FCC) introduced a rule requiring organizations to deorbit satellites within 5 years of a mission’s end. (When we covered the rule, it was merely a proposal; it has since been cemented into something enforceable by law.) Deorbiting a satellite means forcing it to burn up in Earth’s atmosphere. Compared with leaving equipment in orbit until something nudges it toward Earth, deorbiting a satellite allows the responsible space organization to control how the satellite re-enters the atmosphere, thus reducing the likelihood that surviving debris will fall somewhere it shouldn’t.

Illustration of satellites in geostationary orbit.
Credit: ESA

The FCC’s rule only applies to organizations operating within the US, though. It also doesn’t apply retroactively. That means there’s plenty of space junk that will continue to float in space in the absence of intervention. To mitigate this issue, some organizations, from the ESA and NASA to Steve Wozniak’s very own space company, are working on creating space trash removal missions. In some cases, organizations plan to use lasers to nudge debris toward the atmosphere in what’s called “just-in-time collision avoidance.” In others, a giant claw literally pulls trash out of space. While these missions are in the early planning and testing stages, they hold promise—in fact, one such project by the Japanese space sustainability firm Astroscale successfully snagged its first piece of space debris in the summer of 2024.

Finally, a few research teams are working on satellites that burn more reliably upon re-entry into Earth’s atmosphere. For example, researchers in Japan introduced LignoSat, the world’s first wooden satellite, in early 2024; its test run this fall will reveal how practical the experimental satellite really is.