Space is filled with pollution. How can we clean it up? 

Thousands of objects are launched into space each year, but what happens when we no longer need them?

In the South Pacific Ocean, about 2,700 km from any land, you’ll find Point Nemo — the most remote location on Earth.

It’s a dot in the ocean between New Zealand and Chile named for Captain Nemo in Jules Verne’s novel 20,000 Leagues Under the Sea. It’s also in the middle of the spacecraft cemetery. More than 200 retired space objects have been deliberately brought back to Earth here to rest in the depths of the ocean.

After all, what goes up must come down … right?

Not when we’re talking about space.

What is space junk and how much is there?

The original space race was a narrow field. The United States (US) and the Soviet Union going head-to-head for decades, pushing the boundaries of technology, in a competition to conquer space.

Since the two rivals pioneered spaceflight in the 1950s, the cosmos has become crowded. More than 80 countries have operated satellites and in 2021 there were more successful orbital launches (135) than any other year in history; a record already topped for 2022 in October.

Some objects sent into space are brought back to Earth, often near Point Nemo, and others will burn up as they re-enter Earth’s atmosphere.

But what about the rest of it?

Those uncontrolled, defunct human-made objects stuck in orbit are known as space junk or space debris.

They could be as big as an entire satellite, hurtling through space after running out of fuel, or small items that have broken off larger objects or even been dropped, astrophysicist Dr Brad Tucker says.

“A screwdriver and spanner have been space junk because an astronaut dropped them.”

The European Space Agency (ESA) estimates that as of November 2022, there are more than 130 million pieces of space junk larger than one millimetre and 36,500 larger than 10 centimetres.

How often does space junk fall to Earth?

Thankfully, it’s not that common for space junk to land on Earth, which is why some recent instances have made headlines.

In July 2022, Tucker, a Research Fellow at the ANU Research School of Astronomy and Astrophysics, travelled to a property near Dalgety, a small town in the Snowy Mountains in New South Wales, to investigate what two sheep farmers suspected was space junk.

He was the first person to correctly identify the mysterious piece of debris wedged into the ground in a paddock as part of the SpaceX Crew-1 trunk.

“After satellites lose or run out of fuel to keep their orbit stable, they slowly spiral back to Earth as the planet’s atmosphere drags them down. When and where they will come down we cannot predict,” Tucker says.

“This is what we saw with the SpaceX Crew-1 trunk that washed up in the Snowies, and then another piece outside Tumbarumba. It did not have fuel to be controlled and came down over land.”

But overall, there haven’t been that many occurrences of space junk landing on Earth, Tucker says.

“Famously, the US’s space station SkyLab crashed over Western Australia in 1979. There was also a Russian satellite that crashed in Canada in 1978. More recently, we’ve had a Chinese rocket booster crash in West Africa a few years ago, a part of a SpaceX rocket crash in Washington State in the US, and now the Crew-1 trunk in New South Wales.”

If it’s unlikely to crash to Earth, why is space junk a problem?

With thousands of satellites and other objects orbiting Earth, there’s plenty to hit in space as well.

Objects in space are orbiting at seven kilometres a second, which is 10 times the speed of a bullet, and the risk to operational space infrastructure is significant. A stray screw hitting a satellite at intense speed could have massive ramifications on Earth.

Professor Celine D’Orgeville, Director of the ANU Advanced Instrumentation and Technology Centre, explains how we rely on space every day, often without realising it.

“We use space for communications all the time, we relay telephone, internet and banking information — things that really matter to how the world functions,” she says.

“We use space to observe the Earth from above, to know more about climate change, disasters, to monitor transport, a whole lot of things. And in order to do that we need to have satellites orbiting the Earth and we need to make sure these satellites are not going to be damaged by random space debris.

“If any of these satellites came down, it would not just have a big financial impact for the satellite operator, it could take down an entire communication industry and have real, significant consequences for people on the ground.”

What happens if we don’t clean up space?

Concerns about the growing amount of space junk aren’t new. In 1978, NASA scientist Donald Kessler proposed what is known as the Kessler syndrome: that the increasing level of space pollution would lead to a cascading problem of more collisions that create more debris, which in turn causes more collisions, and so on.

“He predicted that if we don’t do anything there will be entire orbits that are unavailable to place more satellites because there’s too much debris and it’s too dangerous to operate at these altitudes,” D’Orgeville says.

So, what can we do about space junk?

As the problem of space junk grows, new solutions to remove debris are emerging. Some of the technology that has been tested included using a harpoon or a net to capture debris. A mission to be led by the ESA in 2025 will use a robotic arm to capture a piece of debris and pull it out of orbit to burn up on re-entry.

But space-based solutions can be expensive and difficult, D’Orgeville says. That’s why she has led research on Earth-based technology that could be used to better track and observe smaller objects in space, as well as prevent collisions that could create more space debris.

While radar and optical telescopes can help find larger pieces of space debris, identifying and tracking the millions of pieces smaller than one centimetre is a challenge. This is where lasers can help.

The laser guide star adaptive optics system helps produce sharper images of objects in space, which are usually rendered blurry or fuzzy due to the turbulence in the atmosphere and the fact they are moving at 25,000 km/h.

“There’s not a one-size-fits-all type of solution that humanity needs to devise. It’s going to be a variety of ways.”

Professor Celine D’Orgeville

Using the laser to probe the atmosphere ahead of an object enables precise measurements of the turbulence. This distortion can then be corrected in real time using the adaptive optics system.

“By the time you’ve made the measurement and you apply the correction with your adaptive optics system, it is correcting for where the satellite is located,” D’Orgeville says. This allows the telescope to capture clearer images, which make it easier to identify and track objects in space.

Other high-power infrared lasers could be used to prevent collisions between pieces of space junk. The intention is to use radiation pressure from the laser light to target debris that’s on a collision path and push it out of its orbit.

“This is about mitigating the risk and frequency of collisions so that we don’t end up in a situation where there are debris-on-debris collisions and then there’s a snowballing effect that makes it really hard to operate any satellite at a particular altitude where that debris is located,” D’Orgeville says.

The technology has yet to be tested to target space debris, but there’s a larger question about its feasibility.

“It’s not entirely clear that you would be able to do this in practice because this might be construed as a threat,” D’Orgeville says.

How can we make space sustainable?

A key step in tackling space waste is trying to limit it in the first place.

“The democratisation of space makes it easier to access for more countries and more organisations, so the number of satellites in space is exploding and that means the amount of debris in space is going to explode as well,” D’Orgeville says.

The best way to prevent a catastrophic scenario with too many satellites and too much debris is to have rules dictating how to dispose of a satellite at the end of its life, she says.

“In the past it was customary to say ‘well once it stops working it’s just going to stay where it is’ and ‘nobody knows where it’s going to go because we don’t control it anymore’. These days there are guidelines that people and countries can decide to follow.”

The United Nations guidelines for the long-term sustainability of outer space are voluntary, but include urging states to consider the long-term sustainability of outer space activities, implement space debris mitigation measures, and develop an end-of-life plan for space objects.

Cleaning up space will require the problem to be addressed on multiple fronts.

“There’s not a one-size-fits-all type of solution that humanity needs to devise,” D’Orgeville says. “It’s going to be a variety of ways.

“At the end of the day, we would like our research work to become obsolete because people will agree upfront how they’re going to deal with their satellites and won’t create pollution in space.”