Decades worth of man-made junk is cluttering Earth's orbit, posing a threat to spaceflight and the satellites we rely on for weather reports, air travel and global communications.
The European Space Agency (ESA) is developing missions to tackle the problem. Proposals include garbage-cleaning spacecraft armed with harpoons, nets or robotic arms.
Over 750,000 tiny fragments are already thought to orbit Earth, and each one could badly damage or even destroy a satellite.
In 2016, a tiny piece of debris punched a gaping hole in the solar panel of Copernicus Sentinel-1A, an observation satellite operated by ESA.
A solar array brought back from the Hubble Telescope in 1993 showed hundreds of tiny holes caused by dust-sized debris.
Dead satellites pose a double danger: they can collide with other spacecraft or be hit by debris themselves, potentially breaking up into tiny pieces that become a hazard in their own right.
The nightmare scenario would be an ever-growing cascade of collisions resulting in what's called a Kessler syndrome - named after the NASA scientist who first warned about it four decades ago.
That could render near-Earth orbits unusable to future generations.
"The big ones are the ones that if they get impacted, will create a cloud of other smaller debris, which in turn could hit other debris," explains Luisa Innocenti, head of ESA's Clean Space office. "And this could start what is called a 'Kessler syndrome,' a chain reaction which is not controllable. The problem of space debris has to be fixed in two ways. First one, we need to stop polluting. And second way, we have to remove the garbage, if you want, the debris."
At ESA's ESTEC Centre in the Netherlands, experts are developing ways to tackle the problem.
E-Deorbit is claimed to be the world's first active debris removal mission.
Jesus Gil Fernandez and his colleagues are designing a robotic arm that can capture out-of-control satellites and remove them from harm's way.
"We use the camera, which is mounted on the smaller robot arm, to mimic, to reproduce, the motion of the satellite around the target, the target satellite that we want to de-orbit, to capture," he explains. "We can move the robotic arms, to grab the launcher adapter ring, so it makes (it) easy to bring it down to the earth and destroy in the re-entry or in the south Pacific Ocean."
Another approach uses nets to capture space junk.
"So, the concept is to, let's say, to mimic what the fishermen do on the sea," explains Michele Lavagna, a professor in flight dynamics at Politecnico di Milano. "And so to have a very large net, to stay away from our debris and mad satellites that is tumbling and moving freely. And then from that distance to keep our net and you just try to wrap all over your satellite."
Experts hope new satellites won't add to the problem.
Ideally - once their missions have come to an end - they would either go into a so-called "graveyard orbit" or return to Earth.
In September 2008, this ESA supply ship was intentionally burnt up over a remote area of the Pacific Ocean.
But tough components, made from titanium and steel, can survive re-entry and hit the Earth.
"Right now, we're trying to understand what happens to the materials we use," says materials engineer Benoit Bonvoisin. "And then we'll see how we can improve them, how we can work on the design and conception of the satellite, how the different parts of the satellite break up in relation to each other upon re-entry, in order to have a satellite which is safer at the end of its life and creates the smallest amount of debris on Earth."