Hackers' Pub

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condition condition	Finds content that satisfies both conditions on either side of the space (logical AND).	`"Hackers' Pub" lang:en`
condition `OR` condition	Finds content that satisfies at least one of the conditions on either side of the OR operator (logical OR).	`#HackersPub OR "Hackers' Pub" lang:en`
`(` condition `)`	Combines the operators within the parentheses first.	`(#HackersPub OR "Hackers' Pub" OR "Hackers Pub") lang:en`

Prof. Sam Lawler @sundogplanets@mastodon.social

12/11/2025, 2:05:39 PM

Public

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!

A plot from Thiele et al. 2025 showing the density of satellites and debris in different altitude bins from 250 to 2000km. The numbers are pretty small because it's objects per cubic km, and not very intuitive. There are a couple of big spikes at Starlink's altitude that are obvious, but nothing else really stands out.

Prof. Sam Lawler @sundogplanets@mastodon.social

12/11/2025, 2:12:07 PM

Public

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

A plot from Thiele et al. 2025 showing average time between encounters that are closer than 1km at different altitudes in Low Earth Orbit. It's mostly in the 1 day range, except where Starlink's very dense orbital shell are, where it goes down below every 15 minutes.

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