First of all, starlink has been jammed in conflict zones.

Secondly, the number of satellites doesn’t really matter, the jamming happens at the end user level not at the satellite.

Finally, where are you getting that 20k number from? It’s not like there’s 20k starlink satellites in LOS to your station at all times. The earth will be obscuring many of those, they are below your feet on the other side of the planet.

Do they have atomic clocks on board?

I was under the impression that Starlink needs GPS for initial acquisition.

They don't need atomic clocks on board. NTP is close enough for most purposes. Sure your error goes up, but often within 100 meters is good enough. The exceptions though do need accurate clocks and are a problem.

For the aviation use case the article talks about 100m is unacceptable. Even for more mundane uses like car navigation 100m accuracy isn’t great.

That's near orders of magnitude more than reality. The only number that matters is the number of satellites that are in communication line of site. A satellite on the other side of the world doesn't help you.

I wonder how many are in view?

gps is 31 total satellites 12,000 miles up

starlink is 10,000 satellites at ~ 300 miles. (and what orbit?)

EDIT: I found this:

-- starlink:

"In any given place there are 3-4 Starlink satellites visible at a time"

https://news.ycombinator.com/item?id=42445512 :)

in december 2024, there were 4,000 starlink satellites in orbit

so starlink is ~ 8 at all times?

-- GPS:

This 24-slot arrangement ensures users can view at least four satellites from virtually any point on the planet.

- https://www.gps.gov/space-segment

Remember there's also BeiDou, Galileo, and GLONASS as well.

Our RTK base station (a Ublox ZED-F9P receiver, with a cheap patch antenna on the roof) can currently see 45 GNSS satellites.

You also need to know where the satellites are meant to be at any one time. That means a stable orbit. Starlink isn't really designed for that.

It then also needs to be signed/secure so that its not spoofed.

Then your signal that your measuring time from needs to be transmitted often enough and robust enough. Plus your time source on the transmitter needs to be accurate enough.

It might be possible with starlink, but you'd also have to trust musk....

They've removed the in-built PNT service