Science Focus - the home of BBC Science Focus Magazine
SpaceX isn't responsible for the rocket that’s about to crash into the Moon after all, but space junk is a serious problem, says UK expert © Getty Images

Space Junk: A rocket crashing into the Moon is the least of our worries, UK expert says

Published: 23rd February, 2022 at 10:26
Subscribe to BBC Science Focus Magazine and get 6 issues for just £9.99

While rockets accidentally colliding with the Moon may seem more dramatic, it’s the growing amount of smaller space debris orbiting Earth that presents the real danger.

Earlier in the year Elon Musk’s SpaceX once again made headline news: a large section of rocket booster belonging to the private spaceflight company that has been careening around the Earth for the last seven years is on a direct collision course with the Moon, the reports ran.


The errant chunk of space junk was spotted by American astronomer Bill Gray, who identified it as the upper section of a Falcon 9 rocket launched from Florida in 2015 that had run out of fuel and become trapped in an ‘chaotic orbit’. Many internet pundits and social media users were, of course, incensed.

Then shortly after Gray's announcement, a group of students based at the University of Arizona’s Space Domain Awareness lab eventually identified the offending piece of defunct space hardware as belonging to a Chang'e 5-T1 rocket launched in 2014 by the Chinese space agency.

However, a spokesperson from the Chinese foreign ministry has since told reporters that this can't be the case as the Chang'e 5-T1 in question safely entered the Earth's atmosphere and burned up.

Regardless of its origin, calculations show that the rocket will crash land on the surface of the Moon on 4 March. But should we be worried about the potential damage it could cause? Not according to Prof Don Pollacco, director of the University of Warwick’s newly formed Centre for Space Domain Awareness.

“It's no big deal,” he says. “The Moon has actually been a handy dump for things like the Apollo spacecraft. Rather than let them float around, most of the first and second stages were crashed into the Moon.”

Read more about space junk:

Not only is it no big deal, for researchers that study objects in Earth orbit it also comes as little surprise.

“There are particular orbits that boosters were just dumped in,” says Pollacco. “There are still about 50 objects, maybe more, that are from deep space adventures that are not tracked now. Space is big, but occasionally something like this happens.”

Taking out the trash

The Centre for Space Domain Awareness launched in September 2021 to study the potential threats of space debris to technology, such as satellites, in orbit around Earth. Particularly those in Low Earth Orbit (LEO), which is classed as anything below 2,000km. And the greater threat is not posed by the more eye-catching events such as rockets colliding with the Moon, but by much smaller fragments of debris, says Pollacco.

According to the most up-to-date statistical estimates carried out by the European Space Agency (ESA) there are currently around 8,000 satellites, functioning or otherwise, in orbit around Earth.

Compare this the 130 million pieces of space debris also occupying the same space and the magnitude of the problem begins to emerge.

What’s more, the overwhelming majority of these, all but about 36,000, are thought to be less than 10cm in diameter. This makes them particularly difficult to track – the errors in measurements of their position are currently in the range of kilometres, Pollacco says.

"Most stuff that's done at LEO is done with radar. And that stems from history, really. It stems from the fact that we have these really big military radar - Fylingdales that are designed to see missiles," says Pollacco. They can be used, not in the most efficient way, to look at things a few hundred kilometres up."

Read more about space junk:

“Once you start getting below spacecraft size, then we don't monitor things well enough to continually know what's there. The numbers of small things, even 10 centimetres in size, are really just not known, except through models, they're not observationally verified, so it's a pretty serious situation,” he says. “There are already some orbits where there is a significant chance of collision. Put it like this - it's not going to get better.”

As these small pieces of debris are travelling at more than 28,000kph – ten times faster than a rifle bullet - any impact they were to make with a spacecraft could potentially cause significant damage.

Moreover, unless action is taken to remedy the situation, the risk of triggering a Kessler event becomes more and more of a possibility. This is a catastrophic scenario named after NASA scientist Donald Kessler, who first proposed the theory in the late 1970s.

It involves a runaway effect in which a satellite that is hit by a piece of space junk breaks into hundreds of tiny pieces of space junk itself, which then hit other satellites and create a domino effect. This could make it extremely dangerous, or even impossible, for rockets to leave the Earth, Pollacco says.

“We're at a situation where it's not too late. But my worry has always been it's only when, say, a spaceship carrying people on it is clobbered that we actually take it more seriously. But now we could deal with it before anything really bad happens,” he says. “But we have to be careful because if we don't do something, then you can be sure that some kind of Kessler event is going to come our way.”

So what options do we have?

“I think it's a mixture of being responsible and abiding by the Outer Space Treaty, which means deorbiting things, paying some sort of levy when you launch so that there is a government or a company that goes to remove the old spacecraft that are there," says Pollacco.


"And then for the rest of the stuff that doesn't deorbit, we need to know where it is. So instead of having error boxes for each bit of debris that are kilometres in size, you need to have a much more reliable measurement.”

About our expert, Prof Don Pollacco

Don is the director of the University of Warwick's Centre for Space Domain Awareness.

Read more about satellites:


Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Science Focus Podcast.


Sponsored content