Starlink routing

Thomas Bellman bellman at
Mon Jan 23 18:08:34 UTC 2023

On 2023-01-23 17:27, Tom Beecher wrote:

> What I didn't think was adequately solved was what Starlink shows in
> marketing snippets, that is birds in completely different orbital
> inclinations (sometimes close to 90 degrees off) shooting messages to each
> other. Last I had read the dopplar effects there were so much larger due to
> relative speed deltas it just couldn't currently be done. If there is more
> out there on that solution, be glad to read up on what info anyone may have
> on that if they can share.

Worst case would be if the satellites are moving directly towards or
directly away from each other.  Each satellite will be moving at a
speed of slighly under 8 km/s, and they will thus approach or depart
from each other with a relative speed of somewhat less than 16 km/s.

I get that for 1310 nm light, the doppler shift would be just under
0.07 nm, or 12.2 GHz:

    l0 = 1310 nm
    f0 = c / l0
    f = f0 / sqrt((1 + 16 km/s / c) / (1 - 16 km/s / c))
    l = c / f ≈ 1310.0699 nm
    f0 - f ≈ 12.2 GHz

In the ITU C band, I get the doppler shift to be about 10.5 GHz (at
channel 72, 197200 GHz or 1520.25 nm).

(Formula from 
first entry in the table under "Summary of major results".)

These shifts are noticably less than typical grid widths used for
DWDM (±50 GHz for the standard spacing), so it seems unlikely to me
that the doppler shift would be a problem.


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