T-Minus: Kessler Syndrome

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Thanks to cheaper rockets and other technological advances, space has never been more accessible. This has created new opportunities for exploration, research, tourism, manufacturing, and more — but it comes at a cost beyond the price of a launch.

Historically, we haven’t been great about retrieving the objects we’ve sent into space, and with the number of new objects in Earth’s orbit now growing faster than ever, the chance of collisions between “space junk” — or between this orbital debris and our active spacecraft — is also growing.

These collisions can create even more space junk, as larger pieces of hardware break into smaller ones. Small doesn’t necessarily mean safe, either. Smaller objects are harder to track, and because objects in low Earth orbit (LEO) are moving at about 17,500 miles per hour, something as small as a screw hitting a spacecraft can cause serious damage.

In 1978, NASA scientists Donald J. Kessler and Burton Cour-Palais hypothesized that there could come a time when we see a sort of chain reaction in LEO, with these collisions in space causing more space junk, causing more collisions — to the point that we lose access to orbital space.

This scenario became known as “Kessler Syndrome,” and for this month’s T-Minus, we’re answering 10 big questions about space junk and the nightmare scenario that could send us back to the pre-Space Age.

How cluttered is Earth’s orbit right now?

NASA and the US Space Force use a combination of satellites, telescopes, and sensors to observe and track any debris in LEO that’s roughly larger than a softball. These systems can also identify smaller pieces of debris, helping us estimate the scope of the problem, but aren’t sophisticated enough to track them.

Other space agencies and governments have programs for monitoring space debris, too, and the number of private companies focused on keeping track of everything going on in space — aka, “space situational awareness” (SSA) — is growing.

Based on this data, NASA estimates there are more than 100 million pieces of space junk larger than 1 millimeter in diameter in LEO. Approximately 500,000 of those objects are between 1 and 10 centimeters, and more than 25,000 of them are greater than 10 centimeters wide.

Where’s all this space junk coming from?

Space junk can be anything from rocket boosters to tools that get away from ISS astronauts during spacewalks, but satellites are the primary source. 

The European Space Agency (ESA) estimates that we’ve placed nearly 20,000 satellites into Earth’s orbit since the start of the space age. About half of those satellites are still operational, while another 3,000 are defunct and just cluttering up Earth’s orbits. The rest have been deorbited: slowed down so they’d burn up while reentering Earth atmosphere or sent to higher “graveyard orbits” away from operational spacecraft.

ESA also estimates there have been more than 650 “fragmentation events” involving satellites — they’ve exploded, broken apart, or collided, turning one or two big pieces of space junk into many smaller pieces. A single collision between an active satellite and a defunct one in 2009, for example, is estimated to be responsible for one-third of all the space debris NASA has cataloged.

In some cases, satellites have been deliberately destroyed in space. 

In 2021, for example, Russia hit one of its own non-operational satellites with a ballistic missile to demonstrate its ability to destroy enemy satellites. In the process, it created more than 1,500 pieces of trackable debris and hundreds of thousands of smaller pieces that endangered the lives of Russian cosmonauts on the ISS.

India, China, and the US have also conducted anti-satellite weapons tests that led to the destruction of satellites in orbit.

Will we know if we’re approaching Kessler Syndrome?

Theoretically, it’s possible that one satellite collision quickly leads to another and another, rendering swathes of LEO unusable in just weeks or months. It’s also possible that the cascade will take decades or even centuries. 

According to Darren McKnight, Sr Technical Fellow at SSA company LeoLabs, Kessler Syndrome will come in three waves:

“We are already in Phase 1,” McKnight told Freethink. “There are some indications of Phase 2 beginning in the next decade. Phase 3 can be stopped with positive and effective changes in behavior and regulation.”

What happens when we reach Kessler Syndrome?

People would just stop trying to use LEO.

“We’d end up with so much debris up there that the probability of collision would be so great that it’s not worth launching satellites…It would render low Earth orbit useless,” John L. Crassidis, a professor of mechanical and aerospace engineering at the University at Buffalo who works with NASA and other US government agencies to monitor space debris, told Freethink. 

That would mean the loss of a lot of our communication and imaging satellites. We might still be able to use high-altitude balloons or solar-powered gliders at suborbital altitudes for some of the science we’re currently doing with satellites in LEO, but it’d be an expensive and subpar replacement.

“There are some missions that can be done like this, but nothing beats space in terms of at least science missions,” Crassidis told Freethink. “You want to be able to get into space.”

We’d probably still be able to use space beyond low Earth orbit — the altitudes we currently use for GPS satellites, TV satellites, space telescopes, and other tech — but there would be the risk of spacecraft being hit while crossing through the congested altitudes.

Depending on how high that risk is, human missions could be deemed too dangerous, meaning no more visits to the moon or beyond.

Is there a way we could come back from Kessler Syndrome?

Once LEO is so cluttered with debris that no one is able to safely operate a spacecraft in it, it’s likely going to stay that way for as long as it takes for orbital decay to cause the debris to reenter Earth’s atmosphere. Depending on its starting altitude, that could be thousands of years.

We might be able to speed up the process with advanced technology — Japanese startup Ex-Fusion, for example, is developing a system to deorbit space junk using lasers shot from Earth — but the challenge of removing a Kessler Syndrome-amount of debris of all sizes is currently far outside our abilities.

“If we get to Kessler syndrome with today’s technology, I hate to say it, we’re screwed,” said Crassidis. 

“If we keep doing what we’re doing … I think within 50-100 years, Kessler Syndrome is going to become a reality.”

John L. Crassidis

So, what are we doing to prevent Kessler Syndrome now?

All the tracking NASA is doing of larger objects in LEO can predict when a collision is likely to occur between active spacecraft or space debris.

“If the chance is greater than one in 10,000, we will call up one of the manufacturers and say, ‘Hey, you probably should move. You don’t have to, but we say you should,” said Crassidis.

Space companies also hire SSA companies like LeoLabs to keep tabs on their spacecraft, providing real-time updates on collision risk so that they can make adjustments when they feel the chance of a crash is too high.

SpaceX, which has more than 6,300 active satellites in its Starlink constellation and plans to deploy at least 5,700 more, takes collision avoidance even further — its satellites automatically adjust their path when the chance of a collision is higher than one in a million.

“Satellites are generally dumb — we have to command a lot of things from the ground,” said Crassidis. “[Starlink] satellites have some smarts on them to maneuver automatically. Information is being directly put onto those satellites.”  

SpaceX’s Starlink internet constellation is dramatically increasing the number of objects in LEO.

In 2022, the US pledged that it would not conduct anti-satellite weapons testing that creates space debris in the future, and 36 nations have since followed its lead — India, China, and Russia are not among them. Nearly 50 private aerospace companies from across the globe have made the same pledge.

The Federal Communications Commission (FCC) also adopted a new rule in 2022 that requires operators of FCC-licensed satellites in LEO to deorbit them within five years of completing their mission to reduce the chance of collisions. The previous time frame was 20 years.

“Avoiding the Kessler Syndrome means avoiding or reducing the risk of collisions in space,” Kate Maliga, LeoLab’s VP of Government Affairs, told Freethink. “That can be done by better tracking of satellites, transparency by satellite operators of where their satellites are and where they are going, [and] responsible disposal of satellites at the end of life.”

Are our current actions enough?

Not likely, according to Crassidis: “If we keep doing what we’re doing … I think within 50-100 years, Kessler Syndrome is going to become a reality.”

What more can governments be doing? 

Reducing the amount of debris we’re generating is step one to avoiding Kessler Syndrome, but because space is an international domain, that’s going to require international cooperation. In 1967, the United Nations adopted the Outer Space Treaty, a basic framework for space law, but Crassidis believes it’s no longer sufficient.

“We don’t have any really modern treaties, and I think we need to,” he told Freethink. “Us and our sister nations are doing some good things [like the new FCC rule] … The problem is that not everybody’s doing this, and we know the bad actors. They’re China and Russia.”

The UN did issue guidelines for debris management in 2010. Those are voluntary and not legally binding under international law, but they could serve as the basis for a new treaty — guideline four, for example, urges nations to “avoid intentional destruction” of on-orbit spacecraft.

“China and Russia blowing up satellites, not a good thing, so I would start with those guidelines and try to slow down the growth,” said Crassidis.

He worries that it will take a tragedy before nations agree to new rules on space debris, though: “A common question I’m asked is, ‘What is it going to take before we start taking this seriously?’ My answer is unfortunately it’s going to take an astronaut being hurt before we finally wake up to this.”

This 7 mm-diameter chip in an ISS window was caused by a tiny piece of space debris.

What more can researchers be doing?

To avoid Kessler Syndrome, we need to get better about tracking debris — and that’s a huge challenge.

“The equations we have for [tracking the motion of] objects in orbit are still not good enough,” said Crassidis. “The smallest effect that we can’t feel here on Earth can have a huge effect in space.”

That means, if we detect an object in LEO, we might think we know where it’ll go, but we’re not certain. Compounding the tracking issue is the fact that we don’t actually know exactly where the object was to begin with either.

“Every sensor has some type of error, so even when I get a hit on an object, I don’t know exactly where that is,” said Crassidis. “I could lose that object for several months. The upper stage of Apollo 12, we lost for 20 years.”

Even if we do get a signal in one part of LEO and then another where and when we expect to see the object again, we don’t actually know it’s the same piece of debris. This issue is known as the “data association problem,” and it’s just one more challenge faced by the SSA community.

The need, then, is for researchers to develop better sensors, algorithms, and other technologies for tracking debris of all sizes — something many are actively working on — as quickly as possible.

What about removing some of the debris that’s already in LEO?

Right now, we don’t have any tech that could cost-effectively remove space junk from orbit, according to Crassidis, but that doesn’t mean the many ideas people have for tugging, zapping, and capturing space junk to get it out of LEO couldn’t be viable options in the future.

“What I like to say is that today’s science fiction is tomorrow’s reality,” said Crassidis. “What we have to do is buy time: get the leaders together, reduce the growth, make sure we don’t get close to Kessler Syndrome and all these technologies that aren’t feasible today, hopefully in 20, 30, 50 years, they will be feasible. Then we can start actively removing debris.”

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