4 ms·

I’m curious about how can they ensure connectivity for a particular area. Is it just that they place a bunch of satellites in orbits and hope that they have eno

I’m curious about how can they ensure connectivity for a particular area. Is it just that they place a bunch of satellites in orbits and hope that they have enough density? Or is there a method to the madness? I am assuming a single satellite covers very small area, in this case a single hexagonal area

wmf 3y ago
The orbits are designed to maximize coverage; it's clearer if you look at the orbital parameters instead of a globe, where you can see that satellites are evenly spaced: https://imgur.com/a/aReh0EQ https://imgur.com/a/aReh0EQ The details are complicated, but each satellite can see quite a large area and any given spot on the ground is within range of 3-4 satellites.
- praveen9920 3y ago
  This makes sense. Thank you for the image
- jessriedel 3y ago
  That's not what that chart shows. The satellites are not evenly spaced over the globe. Most of the satellites are in 53 degree inclination orbits: those orbits have zero coverage at greater than 53 degrees latitude, and they have non-uniform coverage of smaller latitudes. (To see this, consider a constellation of 90 degree inclination polar orbits: the poles clearly have a higher density of satellites than the equator. Similar is true for lower-inclination orbits, albeit to a less extreme degree.)
  - lutorm 3y ago
    those orbits have zero coverage at greater than 53 degrees latitude That's not actually true -- the horizon distance at those altitudes is several thousand km, and one degree of latitude is about 100km, so the satellites are actually visible quite far to the north of there. Of course, they'll be increasingly far away and close to the horizon, so not optimal for reception.
    - jessriedel 3y ago
      Agreed
walrus01 3y ago
The satellites are in constant high speed motion, this is not like geostationary at all. Coverage is a factor of simultaneous density of satellites over an area at my given moment in time, beam forming, and trunk link to earth station capacity.
crote 3y ago
The orbits are designed in such a way that the satellites are uniformly spread across the earth, with each part of the earth having at least one sat covering it at all times. That's the easy part: just launch enough satellites for your orbit altitude. The tricky part is ensuring sufficient bandwidth. You either have to launch additional satellites so that there are 1/2/3/4 sats above every location at the same time, or increase the per-sat bandwidth. The former is probably a good idea anyways for redundancy, but costs a lot of money. Increasing the bandwidth per sat is reasonably easy. They use phased antenna arrays to send a highly directional signal back to earth, which reduces congestion between different areas covered by the same sat at the same time. The limiting factor is probably the downlink back to earth via a ground station - there is only so much data you can reliably pump through a single connection. Their initial set had a 20Gbit downlink[0], but their newest ones can do 4x as much[1]. This bandwidth has to be shared by all people covered by the same sat. So yeah, launch more sats and upgrade the downlink as required. [0]: http://www.satmagazine.com/story.php?number=1026762698 http://www.satmagazine.com/story.php?number=1026762698 [1]: https://www.satellitetoday.com/broadband/2023/02/27/spacex-shares-details-of-higher-bandwidth-v2-mini-starlink-satellites/ https://www.satellitetoday.com/broadband/2023/02/27/spacex-s...
- praveen9920 3y ago
  So, I guess it would become a tricky thing for Starlink if there are a high number of customers around the same location and network congestion becomes a real issue similar to mobile data networks.

wmf 3y ago

The orbits are designed to maximize coverage; it's clearer if you look at the orbital parameters instead of a globe, where you can see that satellites are evenly spaced: https://imgur.com/a/aReh0EQ https://imgur.com/a/aReh0EQ The details are complicated, but each satellite can see quite a large area and any given spot on the ground is within range of 3-4 satellites.

praveen9920 3y ago
This makes sense. Thank you for the image
jessriedel 3y ago
That's not what that chart shows. The satellites are not evenly spaced over the globe. Most of the satellites are in 53 degree inclination orbits: those orbits have zero coverage at greater than 53 degrees latitude, and they have non-uniform coverage of smaller latitudes. (To see this, consider a constellation of 90 degree inclination polar orbits: the poles clearly have a higher density of satellites than the equator. Similar is true for lower-inclination orbits, albeit to a less extreme degree.)
- lutorm 3y ago
  those orbits have zero coverage at greater than 53 degrees latitude That's not actually true -- the horizon distance at those altitudes is several thousand km, and one degree of latitude is about 100km, so the satellites are actually visible quite far to the north of there. Of course, they'll be increasingly far away and close to the horizon, so not optimal for reception.
  - jessriedel 3y ago
    Agreed

walrus01 3y ago

The satellites are in constant high speed motion, this is not like geostationary at all. Coverage is a factor of simultaneous density of satellites over an area at my given moment in time, beam forming, and trunk link to earth station capacity.

crote 3y ago

The orbits are designed in such a way that the satellites are uniformly spread across the earth, with each part of the earth having at least one sat covering it at all times. That's the easy part: just launch enough satellites for your orbit altitude. The tricky part is ensuring sufficient bandwidth. You either have to launch additional satellites so that there are 1/2/3/4 sats above every location at the same time, or increase the per-sat bandwidth. The former is probably a good idea anyways for redundancy, but costs a lot of money. Increasing the bandwidth per sat is reasonably easy. They use phased antenna arrays to send a highly directional signal back to earth, which reduces congestion between different areas covered by the same sat at the same time. The limiting factor is probably the downlink back to earth via a ground station - there is only so much data you can reliably pump through a single connection. Their initial set had a 20Gbit downlink[0], but their newest ones can do 4x as much[1]. This bandwidth has to be shared by all people covered by the same sat. So yeah, launch more sats and upgrade the downlink as required. [0]: http://www.satmagazine.com/story.php?number=1026762698 http://www.satmagazine.com/story.php?number=1026762698 [1]: https://www.satellitetoday.com/broadband/2023/02/27/spacex-shares-details-of-higher-bandwidth-v2-mini-starlink-satellites/ https://www.satellitetoday.com/broadband/2023/02/27/spacex-s...

praveen9920 3y ago
So, I guess it would become a tricky thing for Starlink if there are a high number of customers around the same location and network congestion becomes a real issue similar to mobile data networks.