Week 9: a satellite can be "in view" and still barely useful

Hi all,

For eight weeks now I've been quietly building up a satellite link one piece at a time — can we see a satellite, can we stay in sync with it, which one do we switch to. All plumbing. This week I finally wired in the thing anyone actually asks about: how fast is it?

The idea is the same link adaptation your phone does on the ground. Signal strong? Use a fast, delicate modulation. Signal weak? Drop to a slow, robust one. On a satellite pass the signal swings hugely — weak when the satellite's low on the horizon, strong when it's overhead — so the data rate swings with it.

I ran it on a real Starlink pass over Aberdeen: 40° up at its highest, about five and a half minutes in view. The speed climbed from a couple of Mbps near the horizon to about 16.6 Mbps overhead, and the whole pass delivered around 500 MB.

Then I looked at when that data actually arrived, and it's the bit that stuck with me: half of it came down in the busiest 40% of the time. The peak rate was more than double the horizon rate. The satellite is technically "in view" for the whole five and a half minutes — but the useful part, the part that moves real data, is a shorter window in the middle when it's high in the sky.

Which flips how I think about "coverage." We usually quote it as a yes/no — is a satellite above the horizon? But that number oversells it. Being visible and being useful aren't the same thing, and the gap between them is where the interesting engineering lives.

I also ran a small model to see if you could guess the sustainable data rate from just the satellite's elevation and distance, without any feedback loop. You basically can (R² ≈ 0.999) — though that's partly because my link model is clean and noiseless, so it's less "clever AI" and more "geometry already tells you most of the answer." Which is its own kind of useful.

Nine down, three to go — and with data rate now in the toolkit, the flagship's got everything it needs.

Full write-up on Medium: Visibility Isn’t Capacity: What a Starlink Pass Actually Delivers | by Shaifiqbal | Jul, 2026 | Medium
Code, tests and plots on GitHub: github.com/shaifiqbal/ntn-link-adaptation

More next week.

Shaif