A big old chunk of space debris just fell out of the sky… and it wasn’t the first time!
A very accurate map
What happened?
A piece of a rocket, specifically the separation ring of one, which weighed 1000 lbs (that’s about 450 kg) and was 8 feet long plummeted from the skies and landed on a village in Makueni County, Kenya (don’t worry, no-one was injured).
In case you find it hard to consider how much 1000 lbs is, it is about the same weight as a small bison (of the European variety) or a slender polar bear. It is also, interestingly, the same weight as the cheese wheel gifted to Queen Victoria on her wedding.
Why are we worried (in aviation)?
Several reasons really.
Firstly, refer back to technically accurate map and you will see the region where this fell is not so far from two rather big airports, namely HKJK/Nairobi and HKMO/Mombasa.
Now, the stuff has fallen, didn’t hit an airplane, is very unlikely something will fall again in the same place, granted. But, this one did fall close to an area where aircraft operate and that is a concern in itself because we don’t know where things are going to fall, and…
…the number of times this has happened is on the increase.
Back in 2023, NASA go into trouble for a bit of debris that fell on a Florida home, and in 2024, a piece of a satellite that the European Space Agency described as weighing “about as much as an adult male rhinoceros*” fell into the North Pacific Ocean between Alaska and Hawaii. In 2020, a 20 tonne chunk of a Chinese rocket was tracked as it fell past LA and New York, eventually (mostly) breaking apart into smaller pieces (including a 12 metre long bit of pipe that landed somewhere on the Ivory Coast).
*I am not sure that was their words of a comparison made to the weight their specified.
The issue is that this is happening more often because space is getting more crowded, and unfortunately so are our airspaces, meaning the chances of something impacting an aircraft are increasing.
How much is it increasing by though?
OK, admittedly, it isn’t that much. There are various suggestions, but most sit in the 0.001/year region. That’s about once every 1000 years.
But small probabilities can still add up to big impacts. And these estimates were made before Starlink started adding some 12,000 satellites* into space, and also don’t account for the rising number of defunct satellites in low orbit…
*As of November 2024 they were up to nearly 7000
…And bear in mind the amount of traffic is rising fast (after that Covid blip), as are the number of rocket launches, not to mention plans for things like mega satellite constellations.
ICAO reckons by 2030 there will be around 73 million flights per year. That’s double the 2019 levels.
In the meantime, there were 87 launches in 2015, and 212 in 2023. 128 of those were then abandoned in space and allowed to free fall at their own whim back down again, plus an additional 61 “bits of things” linked to the launch vehicles. Between 2010 and 2022 (inclusive) there were 951 objects that had a radar cross section over 1m.sq that entered in a not controlled way. That’s cumulatively about 1500 tonnes.
Putting all these numbers together and some estimates reckon the impact probability will rise as high as 0.5% (1 in 200) which would equal a possibility of 1 fatality a year of a person on an aircraft that’s been hit by a bit of space debris.
How bad would it be?
The weight required to cause serious damage is surprisingly low, and that’s because of the speed it would be moving at. They reckon just 300g hitting a critical part like an engine, windscreen or important flight surface could be catastrophic because of its bullet like effect, while others think that just 1g could do pretty nasty stuff to windshields.
I mean, just look at what little birds and bits of hail can do…
…And things start out fairly big while in space.
Now, while things do burn up to certain extent, the remaining extent can be between 10% and 40% of the original mass. So, fairly chunky still. This is a particular issue with rockets because they are designed to not fall apart under great heat and pressure and whatever, and they make up about 80% of the mass that is dropping back down.
A big problem is that no-one has really defined the risk very well, particularly the casualty risk which is what is used to determine whether something is going to have to re-enter in a controlled way*. If something has a casualty risk above 1 in 10,000 events then they are supposed to make sure it entries under control… but despite that, 84% of entries exceeded the threshold… and it doesn’t include risk to people in aircraft anyway.
*they can but it is expensive and a lot don’t bother.
Generally, they just say rather vague things like that it shouldn’t “pose an undue risk to people or property” which is pretty meaningless. Without the risk (and acceptable levels) properly defined, getting folk to spend money mitigating it is near on impossible.
Oh no!
Oh no indeed!
But… really… the risk of things hitting aircraft is low. Very low still.
The real impact on aviation is the disruption it causes because they cannot say with any great accuracy where things will land. Take the Chinese rocket example – that ended up seeing France and Spain shutting chunks of airspace for up to an hour while they confirmed it wouldn’t head in their direction.
The problem is, things fall into an orbital decay (and this is quite predictable), but then they are eventually pulled into the Earth’s atmosphere. This is the bit that is unpredictable because how they fall (where they are going to land) is affected by so many variables, and until it starts to get pretty close, they just can’t say with any certainty.
Since the average time to get a NOTAM out is just over an hour, and there is a whole lot of uncertainty until stuff is close, this means they tend to close much more than they need to, leading to big and costly disruptions and delays.
The maybe paths as it gets nearer (blue lines) and the NOTAMs closing bits of airspace (because they weren’t sure)
The issue with tracking stuff
Currently, things in space are tracked fairly well. The Space Component Command (CFSCC) which is part of the… you know what, don’t worry, its loads of acronyms… but the CFSCC is tracking some 32,750 objects in space. It’s pretty advanced and can pick up an object only 50 cm long travelling at 3km per second at a distance of 35,786km away from Earth.
Brilliant I hear you cry! They can see it all!
Alas they can’t. They actually reckon there are about 36,500 pieces of stuff bigger than 10cm (and lower than 50cm), and 1 million or so between 1 and 10cm. OK, most of them aren’t going to survive re-entry, but what they can do is hurtle into other bigger things in space and do bad stuff to them so they fall down (or stop working and mess up stuff like SATCOM and satellite navigation which is a whole other can of worms).
I am off track here though, excuse the pun. What we really want to look at is how they track what comes back to Earth. This all happens with the help of NASA, space surveillance networks, other useful companies and trajectory prediction models… and a whole lot of horribly unpredictable factors.
Space weather induced variations in the upper atmosphere alone create a 10-25% uncertainty just for the timing of the re-entry. That’s about a 9 minute window of not knowing when something might start entering per single orbital revolution. So trying to predict stuff several hours in advance (in order to get warnings out and move aircraft) is hard. And that’s just for when, now try and work out where it will go!
So what are they doing about it?
Well ‘they’ being big important people who know stuff have various plans. First up, they are looking at ways to better track and inform pilots/operators about potentially risky airspace, and to reduce the size of airspace closed. This has already been achieved with some success for launches and controlled re-entries actually.
ALPA sent a letter to ICAO in 2021 telling them to stop relying on the “big sky theory” and they have started to hold workshops to better examine higher airspace operations. In 2023 they put out a bunch of recommendations related to “Aviation Safety and Uncontrolled Space Object Reentries” so they are taking it seriously. This is improving awareness for air crew, ensuring more information is shared and is addressing the increasing impact space stuff is having on Earth based aviation.
The risk of casualties and economic/financial impacts are also being taken a lot more seriously, and stricter rules regarding controlled re-entries for rockets are being considered (although these need to be imposed by governments so it isn’t a quick process). Whose to blame when it does cause problems is being reviewed and will hopefully lead to these being imposed.
And other authorities are focusing on it too. EASA developed a proposal for a higher space operations roadmap in 2023 with many of the studies expected to conclude in 2025, and actions to be proposed following this. This will include more regulations on higher airspace operations, ATC and threat mitigations, and they are working closely with the likes of the FAA to find industry wide solutions.
So for now…
Don’t stress, the risk is still marginal.
Our greatest nemesis in the ‘colliding with aircraft’ range remains the bird by a fairly vast percentage.
But do be aware that the risk is increasing and while the chances of an aircraft being hit by space debris remains very very small, it isn’t tiny, or infinitesimal or well, smaller than small so is something They need to, and are, working on.
Where I got my knowledge from
I pilfered it from the following far wiser/better/knowledgeable places:
https://www.sciencedirect.com/science/article/pii/S0094576524002807
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