Prof. Sam Lawler
Wooo it's up! New paper alert! I will write a summary thread about this paper tomorrow morning when I'm not quite as mentally exhausted!
"An Orbital House of Cards: Frequent Megaconstellation Close Conjunctions" by Thiele, Heiland, Boley, & Lawler https://arxiv.org/abs/2512.09643
Not recommended for reading right before bed. It's real bad up there in Low Earth Orbit, folks.
Prof. Sam Lawler
How do you summarize how unsafe orbit is? This is where I get to tell you about my new favourite forced astronomy acronym, which I spent quite a while thinking about.
We needed a metric. I originally wanted to do something like "Kessler Countdown" or "Kessler Clock" but this isn't a countdown to Kessler Syndrome, it's just showing how bad things are in orbit, and how quickly they could get worse. So, our name for this metric is...
Collision Realization And Significant Harm: the CRASH Clock!
Prof. Sam Lawler
Two incredibly talented students led the project. We figured out a much less hand-wavy analytical way to calculate close approach rates using real data from public catalogues. And then we also ran n-body simulations to double check. They agree very well! And are really scary!!
In the densest part of LEO (Starlink), there are closer than 1km approaches every 15 minutes. 1km sounds like a lot, but remember everything in LEO is moving at 7km PER SECOND
Prof. Sam Lawler
Starlink themselves report an average of 1 collision avoidance maneuver every 2 minutes between Dec 2024-May 2025. So that's another (terrifying) double check on this calculation. https://www.scribd.com/document/883045105/SpaceX-Gen1-Gen2-Semi-Annual-Report-7-1-25?v=0.698
Prof. Sam Lawler
We also did this calculation for the catalogue of satellites, trackable debris, and rocket bodies from 2018, before megaconstellations, showing just how much less safe megaconstellations like Starlink have made orbit.
The densest part of orbit in 2018 had a closer than 1km approach a little more frequently than once a day. Now it's more frequently than once every 15 minutes.
Prof. Sam Lawler
This paper started with a plot showing the density of satellites in orbit vs. altitude that Aaron Boley (professor at UBC) made. I knew this was probably bad, but what does 10^(-7) objects per cubic km really even mean when everything is flying around at 7km per second? It doesn't sound very scary.
I re-made the plot in a hand-wavy way assuming circular orbits, and looking at it in terms of 1km close-approaches instead, and it was a lot scarier. So scary, it was time to write a paper!
Prof. Sam Lawler
This really highlights how incredibly dependent we are on Starlink's continued perfect collision avoidance maneuvers. So far they've done it, but they keep adding more satellites and making it harder.
Other megaconstellations are now launching as well, and they all need to communicate PERFECTLY in order to not crash. Will China talk to Starlink? Will the US gov't secret satellites talk to OneWeb? This is all incredibly important so that we don't destroy LEO.
Prof. Sam Lawler
"In the short term, a major collision is more
akin to the Exxon Valdez oil spill disaster than a Hollywood-style immediate end of operations in orbit. Indeed, satellite operations could continue after a major collision, but would have different operating parameters, including a higher risk of collision damage."
This is why I did a poll here about name recognition for Exxon Valdez a few months ago! (You young'uns go read about it because many of you don't know)
Prof. Sam Lawler
One of the scariest parts of this project was learning more about Starlink's orbital operations. I had always assumed they had some kind of clever configuration of the satellites in the orbital shell that minimized conjunctions, and we would see the number of conjunctions grow over time. But no! It's just random! There's no magic here, it's just avoiding collisions by moving a Starlink satellite every 2 minutes. This is bad.
Prof. Sam Lawler
The CRASH Clock uses the current density in altitude bins (averaged over eccentric orbits) of satellites, rocket bodies, and tracked debris, assuming typical cross sections for each type and orbital speeds. This calculation tells us how long to a collision if all orbital maneuvers were to suddenly stop.
The CRASH Clock is currently* at 2.8 days.
In 2018 it was 121 days.
*This is actually for June 2025 because that's when we ran it. Will update soon!
Prof. Sam Lawler
We set up a CRASH Clock website here: https://outerspaceinstitute.ca/crashclock/
Note that this is a probabilistic calculation. A catastrophic collision could happen sooner than 2.8 days of no maneuvers. In our (extremely computationally expensive) collision simulation, just by random chance we actually got the first collision just 3 hours in.
We are currently well inside the Caution Zone. The probability of collisions happening if no avoidance maneuvers occur is >10% in any 24 hour period.
John Lusk
Is that mv^2/2? All that energy comes from rocket fuel, right? 1/1,000th seems like a lot.
Prof. Sam Lawler
I'll end with the last paragraph of the paper:
"In addition to the dangerously high collision risks calculated here, we are already experiencing disruption of astronomy, pollution in the upper atmosphere from increasingly frequent satellite ablation, and increased ground casualty risks. By these safety and pollution metrics, it is clear we have already placed substantial stress on LEO, and changes to our approach are required immediately."
Prof. Sam Lawler
2 interviews lined up to talk about the CRASH Clock so far!
And I usually say yes to just about every interview request I get, but I got 1 interview request on a non-urgent, non-time-sensitive astronomy topic late on a Friday afternoon asking to talk today or tomorrow. I think I will have to blow that one off and focus on other things.
Prof. Sam Lawler
It's been interesting putting up a high-impact (hopefully no pun there) paper and getting lots of feedback! One (highly respected!) scientist graciously showed us a small error in our calculation, which we have fixed. It's like crowd-sourced peer-review. Interesting.
So, with that fix, the CRASH Clock is now at 5 days instead of 3 days. (If you think that extra time means there's no problem, you missed the point here!)
New from Scientific American: https://archive.ph/6BwqQ
Prof. Sam Lawler
I've seen some truly bad headlines related to this paper. Clearly LLM-written and not checked well. The funniest (saddest) ones seem to imply that 3 days from now, there will definitely be a crash in orbit.
I'm glad conversations are happening as a result of this paper. I hope the right conversations happen with the right people, and maybe some regulations will happen? Probably not fast enough. But I'm still holding out hope (and writing lots of letters to the FCC).
Prof. Sam Lawler
To clarify, I don't think this is at all catastrophic. Just bad. Making orbit less safe with every explosion. Making that CRASH Clock a little shorter, giving operators a little less time to respond, requiring more tracking, more maneuvers, and increasing operating risks in orbit.
Prof. Sam Lawler
Oh hey look, a Starlink satellite "experienced an anomaly" and ejected a bunch of debris. Explosion? Debris hit? Either way, not good..
https://www.pcmag.com/news/starlink-satellite-malfunctions-ejects-debris-fragments
editing to add snark (because that's how I deal with bad news I guess): Don't worry everyone, SpaceX says it'll reenter in a few weeks and totally won't crash into anything! Please ignore the spray of debris that's at basically the exact same altitude as the ISS!
Dr. Eric J. Fielding, PhD
@sundogplanets Our NISAR satellite flies at 747 km. I hope Starlink and its fragments stay far away from that altitude.
AI6YR Ben
Someone lost a satellite
Kessler syndrome will be a delight
To color the holidays skies with sparkling trails
Of humanity's hubris as spaceflight fails
Never mind the satellite fragments flying around
Just listen for the sonic boom sound
What a festive atmosphere
As satellites fall here and there
Sparkly sparkly streaks in the sky
Tell me tell me tell me why
A billionaire gets to own outer space
Why do we have to keep looking at his face
Anyway if it's not this time maybe soon
When the only working satellite left will be the moon
And the skies will be lit up every night
With re-entering broken satellites
#poem #kesslersyndrome #space (human poem)
Dr. Eric J. Fielding, PhD
@sundogplanets The article says that the anomaly was at 418 km altitude, which is low enough that fragments should fall into the atmosphere quickly.
Prof. Sam Lawler
@EricFielding "quickly" is a relative term. A few weeks is still not great odds.
Prof. Sam Lawler
@EricFielding But yes, much better than at 550, or 800km
Steve's Place
@ai6yr @EricFielding @sundogplanets Uh-oh. I just put another one of your poems to music.
Had to cut the "satellite" before "fragments," but it otherwise pretty much survived unscathed, lol.
Steve's Place
@ai6yr @EricFielding @sundogplanets There may be a few minor rearrangements to suit the meter. It has a bit of a Neil Young feel.
In the queue. I guess I should start recording soon. I have acoustic guitar-ready callouses now.
AI6YR Ben
@steter @EricFielding @sundogplanets 😂 Have at it.
AI6YR Ben
@steter @EricFielding @sundogplanets Eager to hear what you make of it!
Steve's Place
@ai6yr @EricFielding @sundogplanets I laid down a couple of rhythm guitar tracks to either turn into one, or to ignore and record again, as always.
Today I discovered that I've been practicing with the acoustic tuned to, not E, not E flat, but D. I recorded with it tuned back up to E. The poor strings never saw it coming.
GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.