Space is turning into a dangerous junkyard
Defunct rockets, satellites and other debris litter the skies. Giant nets, harpoons and robot claws might be part of the solution.
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Astronauts aboard the International Space Station scrambled for shelter last November as their fragile home flew through an unexpected cloud of debris 300 miles above Earth. A Russian antisatellite missile had slammed into a defunct satellite as part of a weapons test, blowing it to smithereens. Any one of the resulting fragments could have fatally pierced the space station.
The astronauts survived that day. But space junk is a big problem, and it’s getting worse. The skies are littered with dead satellites and rocket parts, many dating to the Cold War space race between the United States and the Soviet Union. Zooming among these derelict bits are more than 5,000 operational satellites that feed data into everything from weather forecasts to Google Maps navigation. And their number is growing rapidly.
Just one company — SpaceX of Hawthorne, California — has launched more than 2,000 Starlink internet satellites since 2019, and has plans to launch as many as 40,000 more. It’s like putting a fleet of new cars onto an interstate that’s already piled with junkers: Every move risks a catastrophic collision.
Many space experts warn that orbital congestion is nearing a crisis point. Without stronger international efforts to clean up space, it’s only a matter of time before operating satellites becomes nearly impossible. Each year, as the space around Earth gets more crowded, satellite operators have to spend more and more time directing their machines to dodge others and avoid collisions. “It’s the classic tragedy of the commons,” says Stijn Lemmens, a space debris analyst with the European Space Agency.
And it’s not just that there are more satellites than there used to be. There are also many more players operating them, says Jonathan McDowell, an astrophysicist and space chronicler at the Harvard-Smithsonian Center for Astrophysics. “Back in the day it was either the US or the Soviet government,” he says. “Now it is literally hundreds of startup companies and universities and developing countries — and that’s a huge problem because it’s much harder to coordinate hundreds.”
There’s no easy solution to the problem of space debris. Scientists have been working on ideas such as sending one satellite to grab another one and drag it out of orbit. But there’s far more junk than even an armada of space garbage trucks could remove. And there is no international agreement to force any such cleanup.
Ultimately it will take major shifts involving satellite companies and spacefaring nations — especially the United States, Russia, and China — to keep space workable for future generations.
Nobody’s problem is everybody’s problem
The first piece of space junk arrived in Earth orbit in October 1957, when a Soviet rocket carried the world’s first artificial satellite, Sputnik, into space. Both Sputnik and the discarded rocket parts eventually fell back to Earth and burned up in the atmosphere, but much of the later detritus of the space race did not. The oldest piece of artificial debris still orbiting Earth is Vanguard 1, the US’s second satellite, which launched in 1958.
At first, leaving rocket bits in orbit didn’t seem like a problem. After all, space is big. It just isn’t big enough to accommodate decades’ worth of trash and traffic. “It’s like other environmental problems,” says McDowell. “You start off thinking the oceans are big and you can throw as much crap in there as you like — and then discover that’s not entirely true.”
Since the days of Sputnik, more than 6,100 rocket launches have placed more than 12,000 satellites into Earth orbit, according to a tally kept by the European Space Agency. Some have re-entered Earth’s atmosphere and burned up, but the majority are still in orbit — some functional, some not.
Researchers have long worried about what might happen if space gets too polluted. In 1978, NASA scientist Donald Kessler speculated there might eventually be so much stuff orbiting Earth that pieces would accidentally collide, creating a cloud of fragments that shatter other pieces. A fictionalized version of this chain reaction, known as the Kessler syndrome, appears in the Sandra Bullock movie Gravity when a Russian antisatellite strike creates an out-of-control cloud of debris.
So far, the Kessler syndrome hasn’t quite become reality. But spacewatchers got a shock in February 2009, when an active US commercial satellite called Iridium 33 accidentally hit a dead Russian satellite called Cosmos 2251. The smashup generated nearly 2,000 debris fragments, each at least 4 inches wide, and showed that Kessler-like collisions could indeed happen.
As a result, the US military expanded its efforts to track potential satellite collisions and alert satellite operators of upcoming close calls. Today the 18th Space Control Squadron, at Vandenberg Space Force Base in southern California, tracks the locations of at least 25,000 objects in space. It publishes this information — stripped of sensitive military data — at space-track.org. (Other nations, and some private companies, maintain their own tracking catalogs.)
Nobody wants their expensive satellite to get smashed to pieces by a stray Soviet rocket body from the 1960s. The solution is to watch for impending crashes and move out of the way in time — but that’s harder than it sounds. There are now so many objects in space that satellite operators are swamped with warnings about potential collisions. The European Space Agency, for instance, gets hundreds of alerts each day about threats to its satellite fleet — and can’t afford to move a satellite for every one of those.
Instead, satellite operators have to make judgment calls about how big of a threat the potential collision appears to be. The whole thing resembles an epic game of Frogger, with satellites attempting to make their way through busy lanes of traffic without getting smooshed.
SpaceX alone probably performs thousands of these ‘collision avoidance maneuvers’ every year for its Starlink satellites, says Hugh Lewis, a space debris expert at the University of Southampton, UK. Starlinks are set to automatically move themselves out of the way of impending collisions, so it doesn’t require a person to command each one to move each time. But the sheer numbers of space maneuvers “are really quite astonishing,” Lewis says.
SpaceX has worked to reduce the Starlinks’ contribution to space debris, such as by lowering their planned altitude from around 680 miles above Earth to around 340 miles. That makes it easier for the company to send satellites that have reached the end of their operational lives into the atmosphere, where they burn up.
And SpaceX isn’t the only company launching ‘megaconstellations’ of broadband internet satellites. The UK-based OneWeb has launched more than 400 satellites of a potential 2,000; Amazon’s Project Kuiper is working to soon launch the first batch of more than 3,200 planned satellites; and the Chinese government wants to launch thousands of its own. The end result could be tens of thousands of new satellites around Earth in the coming years.
With all these things headed for orbit, “we have to be a lot smarter about collision avoidance,” says Carolin Frueh, an aerospace engineer at Purdue University. She is among the many researchers working to better estimate the risk of collisions between satellites. Her team uses a telescope in New Mexico to study high-altitude satellites as they pass overhead. By analyzing how the brightness of a satellite changes over time, Frueh can start to work out what it is made of and whether it is tumbling out of control. That type of information helps researchers understand which objects are most dangerous.
Other scientists are pushing to get better realtime data on the locations of objects in space. The space-track.org catalog has much of this information, but it’s neither complete nor easy to visualize. One new effort is a ‘satellite dashboard’ that tracks close approaches. And at the University of Texas in Austin, astrodynamicist Moriba Jah has developed additional web tools that draw on multiple sources of information to depict the locations of objects and the risks of upcoming satellite collisions.
Knowing exactly where everything is in space at any given time is the best way to manage the growing threat of space debris, Jah argues. It’s like air traffic controllers knowing the location of planes around LAX accurately enough to direct them to land and take off without crashing into each other every few minutes. Congestion is OK if it’s managed.
Tensions rise as the skies grow crowded
Space debris is a monumentally tricky problem because no one is in charge of solving it.
Countries’ interactions in space are governed by the 1967 Outer Space Treaty, which holds that nations are responsible for items launched into orbit from their soil. But there is no international enforcement mechanism for scofflaws, aside from peer pressure.
That is effective, to a point. Imagine a navy that left a huge defunct ship listing in international waters, said Darren McKnight, an analyst at the commercial debris tracking company LeoLabs, in a recent webinar hosted by the University of Washington. That navy would be under enormous pressure from other nations to clear the ship out.
But with SpaceX and other companies now launching tens of satellites at a time, geopolitical tensions are soaring. In December, the Chinese government formally complained to the United Nations about two close calls between its space station, called Tiangong, and SpaceX’s Starlink satellites. In July 2021 and then again in October 2021 — when Tiangong had three astronauts on board — the station had to move out of the way of potential collisions with Starlinks. The complaint says the October near-miss involved a “continuously manoeuvring” Starlink whose motion could not be predicted so that “orbital errors were hard to be assessed.” The close calls were a danger to the life of Chinese astronauts, the complaint says, which contradicts the intent of the Outer Space Treaty. SpaceX did not reply to Grid’s request for comment.
There are only a couple of major players in the space-debris game. More than 90 percent of the stuff in Earth orbit traces back to the United States, Russia and China. The single largest debris-generating event in the history of space was a Chinese antisatellite test in 2007, which created more than 3,000 fragments. (The Russian antisatellite test in November left at least 1,500 metal shards in orbit, instantly doubling the risk of debris hitting the International Space Station.)
Along with Russia and China, the U.S. and India have also conducted antisatellite tests — more than 20 in total since 2005. Such tests not only create a lot of debris, they also push it higher in the atmosphere, making it last longer because it doesn’t fall out as readily.
Antisatellite tests are one of the most unpredictable sources of space debris since they happen without warning. How much debris they ultimately generate depends on the type of satellite that was blown up, the angle at which it was hit and the altitude at which the debris was generated, among other factors.
There are also much larger pieces of space debris, like the big derelict Soviet rocket bodies that can weigh up to 9 tons. These huge relics no longer have any propellant with which operators could safely guide their descent. The chance of someone on the ground getting hit by space debris is vanishingly small but is not zero; in January, a Russian rocket stage re-entered the atmosphere uncontrollably after it failed during launch.
In the early 2000s, a committee of international space agencies recommended that anything launched into orbit should be brought back to Earth within 25 years after the end of its operational lifetime. “The 25-year rule looked great 20 years ago,” said Lewis. But today, with so many satellites being launched so quickly, it’s no longer as useful, he said.
China’s U.N. filing serves as a reminder that there’s no international legal enforcement when something goes wrong, said Giuliana Rotola, a Ph.D. student at the Sant’Anna School of Advanced Studies in Pisa, Italy, who studies space law and space sustainability. “It’s something we really need to take care of now and that needs to be done in a harmonized way,” she said. “We cannot have different legislations doing different things.”
Like climate change, space debris is “a problem that we know is coming, where the big negative effects are coming in future decades but we need to take action now,” said Brian Weeden, a space security expert with the Secure World Foundation. And as with carbon dioxide emissions, different nations have contributed different amounts to the problem over decades.
All space-debris enforcement currently happens at the national level. “If you are a satellite company and you want to launch a bunch of stuff, you will have to get a license from someone,” Weeden said. “Odds are you’ll be asked, ‘How will you mitigate space debris?’”
In the U.S., federal agencies are expected to abide by a set of standard practices created in 2001 and updated in 2019. That includes rules such as having a no more than 1-in-1,000 chance of a satellite blowing up accidentally and creating debris. These rules are also why NASA recently announced plans to safely guide the International Space Station to crash in an ocean after it reaches the end of its lifetime, likely in 2031.
Any future international regulations on space debris would likely have to be worked out through the U.N.’s Committee on the Peaceful Uses of Outer Space. They might take the form of regulations for who can send satellites to which orbits — analogous to the international agreement that regulates who can broadcast in which portion of the radio spectrum — or other restrictions on licensing launches.
More immediately, Weeden and others have called on the U.S., Russia, China and India to commit to stopping antisatellite tests that involve blowing things up in orbit. “The real risk we see here is this creation of orbital debris that threatens other satellites and pollutes the environment over the long term, much longer than the test itself,” he said. There may be political traction to the idea of an antisatellite test moratorium; in December, the U.S. deputy secretary of defense told a meeting of the National Space Council that she would like to see an end to debris-generating tests.
Send in the space harpoons and nets, or maybe just a cosmic trash truck
For the last couple of years, various parts of the U.S. government have been trying to take action on space debris — with only moderate success so far.
In 2018, the Trump administration began an effort to shift responsibility for tracking objects in space from the Department of Defense (where the Space Force runs space-track.org) to the Department of Commerce. The idea was to provide more transparency by reducing ties to the military and by strengthening ties to the commercial space industry. The shift has not yet happened, though, because Congress has not granted Commerce the regulatory authority to take over the tracking of space objects. But the department is preparing for the possible change; last week it released a prototype for a space-tracking and space-traffic catalog.
Under President Joe Biden, the White House’s Office of Science and Technology Policy (OSTP) is working to update Trump-era recommendations on what the government should do next about space debris. The aim is to have a draft available for public review by summer, Ezinne Uzo-Okoro, the OSTP’s head of space policy, has said. In the meantime, the Space Force is trying to create incentives by funding a competition for companies to come up with ideas for removing space debris. Those proposals are due Thursday.
Economic incentives may be one of the best ways to force action on space debris, said Akhil Rao, an economist at Middlebury College. Outer space is a valuable resource that is unpriced and hence gets overused. “It’s a pretty classic case of open access to a common resource leading to overuse of that resource,” he said — like how the high seas are overfished.
To change that, governments could consider requiring anyone who wants to launch to space from their soil to pay some sort of cost that reflects the value of outer space, Rao said. That might involve bonds like those used in licensing oil and gas wells, which require the well operator to have a plan for cleaning up the well at the end of its lifetime. Or it could be some bounty placed on bringing down derelict rocket bodies — like bringing glass bottles to your local recycler for a refund.
Hauling down the big old pieces of space junk could be one of the most effective ways to clean up space. In one recent listing of the 50 most dangerous pieces of space debris, the top 20 were all large Soviet or Russian rocket bodies, most of them from before the end of the Cold War. (Just for fun, Lewis once calculated what would happen if all 50 of these objects blew up at once. He found that the chance of catastrophic space collisions quadrupled, although it soon declined as many of the fragments began falling out of orbit.)
At least one company, Astroscale of Japan, is asking OSTP to recommend that the U.S. government fund a project to send a probe to a piece of space debris and explore ways to either upgrade it or bring it back to Earth. Astroscale tested some of this technology last year when it launched two spacecraft that were magnetically locked together, and then disconnected and re-connected to one another while floating in space. Future spacecraft could carry one of Astroscale’s docking plates on board, so that when their lives end a little Astroscale probe could fly up, attach itself to the plate and refuel the satellite — or drag it into the atmosphere to burn up.
There are plenty of other ideas for ways to snag space debris. In 2019, a European mission called RemoveDEBRIS fired first a harpoon and then a net at a piece of debris, testing ways to snag and drag it out of orbit. Another European effort, called ClearSpace, aims to test a grappling mechanism to grab debris with a mission to launch in 2025 or 2026.
Engineers are currently designing ClearSpace as a sort of giant mechanical hand that could reach out and close around its first target, which is part of a leftover European rocket stage. One big challenge is figuring out how to grapple with a spinning piece of space debris, said Lemmens: “It is a hard task to grab an object which is not designed to collaborate with you.”
If it works, ClearSpace will fly down toward Earth with the piece of space debris and both will burn up on re-entering the atmosphere. It would be the world’s first demonstration of removing a piece of debris from orbit. Then the company could launch more gigantic space hands and grab more space junk to take out of orbit.
As sci-fi as these missions sound, they will always have the shadow of weaponization lurking over them, warns Frueh. Any mission that could spear a science satellite with a space harpoon could also spear another nation’s spy satellite against its wishes.
Cleaning up space debris is ultimately about making space a safer place for satellites to operate, Lewis said. “What I find incredibly ironic is that space is great for pushing forward with sustainable development goals,” he said. “But it’s based on a single-use paradigm of, we build a spacecraft, we fly it and we dump it.”
Keeping space clean for future generations is a human rights issue, said Rotola. Many nations have not yet had the opportunity to develop their space programs, and they deserve equal access to space as much as the early arrivers such as the U.S. and Russia. In that sense, environmental protections in space are an extension of environmental rights on Earth. “It’s important that we recognize that the environment that needs to be protected is not only this small planet but also all the environment that is around our Earth,” she said.
And that extends all the way to the moon, Mars and beyond, said Frueh. As NASA and other space agencies plot missions to the moon — more than half a dozen are expected this year alone — Frueh has been working to understand whether humans might clutter up the space there as well. “As we go farther out from Earth, the problem of where to put stuff at the end of its mission kind of exacerbates,” she said.
Beyond the Earth, there is no atmosphere to burn up objects that are re-entering from space. So space explorers need to extra-careful around the moon and Mars so that they don’t crash their junk onto the surface. This is about to be demonstrated dramatically for the first time — on March 4, a rocket part likely left over from a 2014 Chinese launch will crash into the moon. It will be the first piece of space junk to unintentionally hit the moon.
Which means the problem of space debris is about to go interplanetary.
An earlier version of this story misstated the date of a Chinese rocket launch. This version has been corrected.