On 8 March 2024, Florida resident Alejandro Otero was minding his own business when a metal object weighing 0.7kg quite literally fell from the sky and tore through his house, smashing through the roof and, subsequently, the two floors below it.
A month later, on 15 April, NASA confirmed what many had already suspected: that no, this was not a sign from God, but was instead a lump of an old battery pack from the International Space Station (ISS) that had failed to fully burn up on reentry.
Thankfully, no one was hurt, but according to Prof Aaron Boley, an associate professor of astronomy and astrophysics at the University of British Columbia, events like this are just a sign of what’s to come as our orbital space gets too crowded.
“We’re getting more and more of these types of things happening as more actors begin launching things and operating in space, and it's just a matter of time before somebody gets seriously hurt.”
With tens of thousands of satellites planned for launch in the next few years, concern is growing that we’re using low earth orbit (LEO) – the region of space around Earth where most satellites are located – unsustainably.
For Boley and others campaigning on this issue, casualty risk or property damage is just the tip of the iceberg.
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The scale of the problem
A lot has changed since the Soviet Union launched the first ever satellite, Sputnik, on 4 October 1957.
According to the satellite tracking website Orbiting Now, as of 18 April 2024, there are 9,822 active satellites orbiting our planet, along with 2,770 inactive objects.
The satellite internet constellation Starlink, owned by Elon Musk’s SpaceX company, launched its first batch of 60 satellites in 2019. It now accounts for 6,188 of the satellites in orbit (63 per cent), and reportedly plans to put as many as 42,000 into orbit.
Starlink isn’t alone, mind you. Applications for approximately 65,000 satellites have been filed by the likes of SpaceX, OneWeb, Guo Wang and Amazon.
According to a recent article in Nature Sustainability co-authored by Boley, the number of satellites in LEO is now on track to exceed 100,000. Add to that the 25,000 pieces of debris larger than 10cm known to exist, and approximately 500,000 smaller than 10cm (that’s according to NASA’s best guess), and you begin to get a sense of just how busy things are getting up there.
So, hundreds of thousands of objects, flying around Earth at thousands of miles per hour. What could possibly go wrong?
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The problem itself
While there are tremendous benefits to putting satellites into space – global connectivity, security, climate monitoring and scientific research, to name a few – there are some major pitfalls to filling our orbital space to the brim.
Boley explains that the main problem is fourfold:
- The impact on dark and quiet skies for astronomical observations.
- Collision risk in space (think Sandra Bullock in Gravity at the extreme end of this scenario).
- Pollution of the upper atmosphere, caused by defunct satellites burning up.
- Casualty and damage risk on impact, as with Alejandro Otero’s home.
Solving one of these issues in isolation, or at least identifying a limit for it, might be fairly simple. Sadly, nothing in space is ever straightforward.
“When it comes to the Earth-space system, you can change one thing and accidentally affect other parts of that system. In fact, you almost certainly will,” says Boley. “You turn one knob and the other one turns on you.”
For example, you can reduce the likelihood of objects hitting people’s houses by designing satellites to completely burn up in the upper atmosphere. But this, according to a 2023 study, pollutes the stratosphere with harmful materials like ozone-depleting metals.
To get around that, you could just leave stuff up in space and not have it come down at all. But then you increase the risk of collision and make it harder for telescopes to get a clear view of the night sky. And so on and so forth.
So, what’s the limit for stuff we can put up there? Is it 100,000 or 20,000 or somewhere in between? Boley says we don’t know, and therein lies the problem.
What’s the solution?
Thankfully, the space sector hasn’t been idle in addressing these issues, and progress is being made in at least some areas.
Pressure from the astronomy community, for example, has led SpaceX and Amazon Kuiper to modify their satellite designs, essentially making them less shiny. While this doesn’t fully resolve the issue of telescopes being able to see them, it at least helps.
To avoid such measures being optional moving forward, the International Astronomical Union has established a Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference. The topic of dark and quiet skies has since found its way onto agenda sheets at the UN, G7 and the Council of the European Union.
Avoiding collisions between satellites and debris (or other satellites) requires ensuring all satellites are fully manoeuvrable and capable of tracking what’s around them. Believe it or not, a lot of collision avoidance today is still done manually.
As the European Space Agency explained in a 2019 blog post: “As the space highways above Earth get busier and close approaches become more common, the current manual process of calculating collision risks and determining how spacecraft should respond will be far too slow and time-consuming to be effective.”
But Boley cautions against trying to “tech our way out of” this rabbit hole. “There’s always this belief that if we could just get better technology, then that will solve our problem.
“Things like automatic collision avoidance are great in principle, but if by getting them to work, companies are motivated to put even more satellites into that operating space, then you take away any environmental advantage.”
As for what we’re burning up in the atmosphere, Boley explains that we’ve already surpassed the amount of certain materials we’d expect the atmosphere to naturally absorb from passing meteorites.
Most new satellite constellations are designed with a lifespan of around five years in mind. That means every five years we can expect to have tens of thousands of satellites deorbit and burn up into the upper atmosphere, where, experts say, material will accumulate indefinitely.
Solving this is tricky, given the aforementioned risk of fatal impacts with the ground. “I think it would be great if we slowed down just a bit here to really understand what we’re doing to the environment and what the boundaries for safe operation are,” Boley says.
Despite this complex myriad of domino effects and disaster scenarios, Boley remains hopeful that we can develop space sustainably and reap the rewards of expanding further into space. “It’s the difficulty of operating in space and the shared risk that provides a lot of motivation for humanity to come together and solve this problem. I hope that that continues, although there’s no guarantee.”
About our expert
Aaron Boley is an associate professor and Canada research chair in planetary astronomy in the Department of Physics and Astronomy, at the University of British Columbia. He is also the co-director of the Outer Space Institute, a transdisciplinary organisation that addresses challenges associated with ‘New Space’, and co-author of the book Who Owns Outer Space?: International Law, Astrophysics, and the Sustainable Development of Space.
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