31 How Much Junk Is in Space?

We humans are messy creatures. We leave garbage all over the Earth and we also leave it in space. More than seven thousand satellites are in orbit around the Earth, but most of them are not working.

Satellites are machines and, like all machines, they wear out. That means there are a lot of dead satellites in space. In 2009, a dead Russian satellite called Cosmos 2251 collided with an American communications satellite called Iridium 33. When these two objects hit, their two speeds together added up to more than forty-two thousand kilometers per hour. Needless to say, both satellites were completely blown to bits, and those bits added to the growing problem of space junk.

Dead satellites are only part of the space junk, though. Every time a satellite is launched into space, it rides on the back of a rocket, so there are used rocket boosters scattered in orbit. But there are also about a million tiny bits of debris—burned-out boosters, nuts and bolts, even flecks of paint—circling the planet, all contributing to the increasing problem of garbage in space. In short, space is littered with potential hazards. The more objects we send into space, the greater the chances of them colliding with other objects, making more pieces of junk and more chances of collisions, which also create more junk… If this keeps up, there will be so much debris in space, no one will be able to go up there without getting hit.

All these pieces of space debris are scattered over an extremely wide area, but each one of them is moving incredibly fast—up to twenty-eight thousand kilometers per hour, which is faster than a bullet. A collision with a piece as small as your finger can have the explosive force of a grenade and could completely destroy a multimillion-dollar satellite, or worse, threaten the lives of astronauts in space.

Satellites are launched just about every week, but there’s rarely a plan to dispose of them when they come to the end of their lives. Fortunately, some of them take care of themselves.

Objects in low Earth orbit, including space stations, tend to take care of themselves because they’re not entirely out of the Earth’s atmosphere. Even at three to four hundred kilometers above the Earth, there is still a tiny amount of atmosphere that objects fly through. That atmosphere drags on the satellites, causing them to slow down over time, so their orbits naturally decay until they plunge back into the thicker atmosphere below and burn up from air friction. In fact, sometimes what looks like a shooting star is actually a piece of space junk falling back to Earth. Even the International Space Station, four hundred kilometers above the surface of the planet, experiences a tiny bit of atmospheric drag, so the station has to be boosted back up on a regular basis. One day, it, too, will meet a fiery end in our atmosphere.

For the most part, smaller satellites will burn to nothing on reentry, so we don’t have to worry about them too much. It’s only when larger things—like space stations—burn up that some fragments of debris survive all the way to the ground. Of course, no one wants to be hit by a piece of space junk falling from the sky, but the problem comes when we try to predict exactly when and where the debris will fall.

A lot of space junk is moving so fast that it skips across the top of the atmosphere like a stone skipping across a pond. And like a stone, how far the pieces go and when they stop depends on a lot of factors: the shape of the stone, the angle it hits the water, and any waves that could get in the way. Some stones dig in immediately, while others seem to go on forever before coming to a stop and dropping straight down.

Dead satellites are odd-shaped and often tumble end over end, so how they will behave in the air is uncertain. The final impact point cannot be predicted with any accuracy until the last few orbits, and even then there is uncertainty.

That was what happened in 1979 with the fall of Skylab, the first American space station, the Russian space station Salyut 7 in 1991, and more recently, the Chinese space station Tiangong-1 in 2018. Scientists tried to reassure the public that there was little to fear by pointing out that the odds of being hit by debris falling from the sky are extremely low because very little of it actually reaches the ground. Also, most of the planet is ocean, so it is more likely that the pieces would fall in water than anywhere on land.

Tiangong-1 fell in the Pacific Ocean, but both Skylab and Salyut 7 overshot their predicted impact points. Bits of the American station fell down in Australia, and parts of the Russian station came down in Argentina. Thankfully, no one was hurt in these cases, but it shows how difficult it is to pin down the final resting place of an uncontrolled large object.

The best-case scenario was the intentional de-orbit of the Russian space station Mir in 2001. The 140-ton complex was the largest object to reenter the Earth’s atmosphere, and it was controlled from the ground. Using a small rocket, the operators on the ground drove Mir toward the Pacific Ocean where the pieces fell harmlessly into the water. It makes you wonder how the International Space Station, by far the largest object ever to fly in space, will be brought down when its mission is over, sometime after 2024.

The rest of space junk in higher orbits is a much bigger problem. Because that junk is completely above the atmosphere, it will take thousands of years to drop to Earth, if it ever does. And with an ever-increasing number of satellite launches in the future, the amount of debris and derelict satellites will only increase as time goes on. If we don’t do something about the problem, we could get to a point where it will become impossible to launch anything into space because of the hazard of running into junk.

And let’s not forget the many tons of equipment that were left on the moon, such as lunar modules and rovers, boots, scientific equipment, and robot landers that no longer work. There are several dead satellites in orbit around the moon as well.

Even Mars has space junk already, with dead satellites in orbit around the red planet as well as dead robot landers and rovers on the surface.

So what can be done to clean up all of this space junk?

There are a range of ideas. The European Space Agency has a plan to send up a robot to capture derelict satellites, either with a mechanical arm or a net, and drag them down into the atmosphere. But that would require a huge number of robots.

Other organizations suggest sending up refueling robots that will act as space gas stations to fill the satellites’ fuel tanks and keep them operating longer.

Other ideas are a little more radical. The Australians have proposed using a high-powered laser to blast the very small pieces out of orbit. The Chinese are working on a similar plan. But some people worry that a laser could be used as a weapon and weapons are not allowed in space… yet.

All of these ideas are very expensive because the amount of junk in space is huge and spread over such a vast area. Any cleanup method will take decades.

The best idea is to stop leaving junk up there in the first place. Already, we’re designing rocket boosters that return to Earth for recycling. Future satellites should carry extra fuel that can be used to dispose of themselves at the end of their useful lifetimes.

There was a time when people didn’t think twice about throwing garbage out a car window. Now littering is against the law. It is time for a similar law to be put into place for the entire international space community so we can clean up the dangerous litter that surrounds the planet and ensure we can safely travel through and explore the cosmos for many years to come.