Appreciate that. Definitely becoming clear to me that a lot of my knowledge here was rusty. Lots of papers on this specifically (Doppler effects on optical ISL) that I need to call in some favors to get access to.
Thanks! On Mon, Jan 23, 2023 at 1:08 PM Thomas Bellman <bell...@nsc.liu.se> wrote: > 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 https://en.wikipedia.org/wiki/Relativistic_Doppler_effect > 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. > > > /Bellman > >
