Comment by schiffern
1 year ago
>these laser links are used in bursts and the link stays established only for a few tens of seconds or minutes, until the satellites move away
The way Starlink satellites are in orbit, the same satellites will remain "ahead" and "behind" you in the orbital plane. Those laser links (specifically!) will remain relatively persistent. This arrangement is similar to Iridium FYI.
FTA: "in some cases, the links can also be maintained for weeks at a time"
FTA: "in some cases, the links can also be maintained for weeks at a time"
I think there is a lot of variance. The article also states about 266,141 “laser acquisitions” per day, which, if every laser link stayed up for the exact same amount of time, with 9000 lasers, means the average link remains established for a little less than an hour: 9000 (lasers) / 266141 (daily acquisitions) * 24 * 60 = 49 minutes
So some links may stay established for weeks, but some only for a few minutes?
I would guess that the links between satellites on the same orbit stay for weeks, but the ones that cross between orbits have to constantly re-established.
Correct.
I believe Starlink (like Iridium) doesn't even try to establish connections "across the seam," ie the one place the satellites in the adjacent plane are coming head on at orbital speed.
This make side-linking easier because the relative velocity is comparatively low, but in general you unavoidably still need to switch side-link satellites (on one side) twice per orbit. Hence 49 minutes: this average must be calculated per connection not per second, so the front/back links (plus random noise) count less, so it only drags the average from 45 minutes up to 49 minutes.
2 replies →
Partially! There are also ascending and descending satellites meeting. Ascending and descending doesn't mean altitude but in a "2D view" sense. See https://www.heavens-above.com/StarLink.aspx
Thanks, this is an important point. I missed the fact that Starlink's orbital planes actually cover the full 360° of RAAN[0], not just 180° like Iridium did (presumably to minimize the number of satellites).
So actually this Iridium-type "seam" disappears, meaning that every satellite should always have co-orbiting "neighbors" on both sides. Cool!
[0] https://en.wikipedia.org/wiki/Right_ascension_of_the_ascendi...