5 ms·

I don't know how they're going to get 25/35ms hops. If they're using low orbits to reduce latency, the surface coverage is going to be lower so they're going to

by setq 10y ago

I don't know how they're going to get 25/35ms hops. If they're using low orbits to reduce latency, the surface coverage is going to be lower so they're going to have to mesh them in some way to span large areas. That means routers and intelligence which means uplink, interlink, downlink hops in both directions. 600ms here we come again.

tarikjn 10y ago
Here is the part you missed: "Optical inter-satellite links permit flexible routing of traffic on-orbit."
- setq 10y ago
  It's still EM radiation. Takes the same amount of time to propagate between two points in a vacuum. Line of sight optical in space is going to be very difficult. Even relativistic effects need to be considered at very high frequencies as they can cause phase shifts. Managing that on a mesh hurts my head.
  - tarikjn 10y ago
    Thought you meant ground re-routing, I am the one who read you initial comment too fast, and missed the mesh part. Anyway, what makes you think that routing at such a low orbit should be significantly slower than ground-routing?
bosdev 10y ago
It's all very clearly spelled out in the document. They are going to operate them in low earth orbit, each satellite covering a small area.
ygaels_armpit 10y ago
30ms and Telstra is out of business in Australia. Finally, bring it on. Actually, give me 2000ms and a Musk plan, I'll take that over Telstra.
ryan-c 10y ago
Another thing to consider is that fiber slows down light substantially vs radio and laser comms.
- setq 10y ago
  It does indeed. However not as much as processing a signal may do. I'll extrapolate further. I worked indirectly with satellite systems back in the late 1990s. You've got two ways of handling satellite data: 1. Uplink/downlink. This is the most primitive and I understand still the most common. You RX, strip the carrier off, mix it with a new carrier, amplify it and send. There is no intelligence other than the uplink and downlink frequencies. Bandwidth of both of these is pretty wide. Ergo, latency is minimal, power efficiency is high. The satellite doesn't have any idea what the signal means. 2. Decode/retransmit. This you need to RX it, strip the carrier out, demodulate it possibly thousands of channels individually spanning a massive bandwidth, intelligently decide what to do with it while buffering it, mix with one of many new carriers, amplify, retransmit. Latency high, power efficiency low. The latter requires some serious routing power which isn't necessarily available either cost efficiently or reliably of the shelf. Getting something like that which is rad hardened isn't likey to succeed and you can't just launch three redundant core 2's to do it like Dragon. Imagine launching a radiation hardened 4G base station. That's a good analogy.
schiffern 10y ago
> That means routers and intelligence which means uplink, interlink, downlink hops in both directions. 600 ms here we come again. The story from Musk is 20-30 ms latency anywhere on Earth. https://www.youtube.com/watch?v=AHeZHyOnsm4&t=7m00s https://www.youtube.com/watch?v=AHeZHyOnsm4&t=7m00s Fiber has an order of magnitude greater number of hops/routers/repeaters, moves 50% slower, and has to travel more distance to route around continents. See https://news.ycombinator.com/item?id=12984991 https://news.ycombinator.com/item?id=12984991 In the linked video Musk says 4 hops to go from Seattle to South Africa, so they're skipping satellites. It works out that at 1100 km altitude they have vacuum line-of-sight for any satellite within 6000 km ground track in any direction. >I don't know how they're going to ... >Managing that ... hurts my head. It is indeed a Hard Problem. https://www.youtube.com/watch?v=AHeZHyOnsm4&t=5m18s https://www.youtube.com/watch?v=AHeZHyOnsm4&t=5m18s >So it's something that would both provide optionality for people living in advanced economies, as well as people in poor countries that don't even have electricity or fiber or anything like that. So it's a real enabler for people in poor regions of the world and it gives optionality for people in wealthier countries. >So I think it's something that definitely needs to be done. And it's a really difficult technical problem to solve. So that's why we need the smartest engineering talent in the world to solve the problem. >And, you know, at the same time to make sure that we don't create Skynet. So... [laugh] Ironically, the server room at Spacex (jokingly!) was called Skynet. [laugh] Though fate has a great sense of irony, so we really need to make sure that doesn't come true...

by setq 10y ago

tarikjn 10y ago

Here is the part you missed: "Optical inter-satellite links permit flexible routing of traffic on-orbit."

setq 10y ago
It's still EM radiation. Takes the same amount of time to propagate between two points in a vacuum. Line of sight optical in space is going to be very difficult. Even relativistic effects need to be considered at very high frequencies as they can cause phase shifts. Managing that on a mesh hurts my head.
- tarikjn 10y ago
  Thought you meant ground re-routing, I am the one who read you initial comment too fast, and missed the mesh part. Anyway, what makes you think that routing at such a low orbit should be significantly slower than ground-routing?

bosdev 10y ago

It's all very clearly spelled out in the document. They are going to operate them in low earth orbit, each satellite covering a small area.

ygaels_armpit 10y ago

30ms and Telstra is out of business in Australia. Finally, bring it on. Actually, give me 2000ms and a Musk plan, I'll take that over Telstra.

ryan-c 10y ago

Another thing to consider is that fiber slows down light substantially vs radio and laser comms.

setq 10y ago
It does indeed. However not as much as processing a signal may do. I'll extrapolate further. I worked indirectly with satellite systems back in the late 1990s. You've got two ways of handling satellite data: 1. Uplink/downlink. This is the most primitive and I understand still the most common. You RX, strip the carrier off, mix it with a new carrier, amplify it and send. There is no intelligence other than the uplink and downlink frequencies. Bandwidth of both of these is pretty wide. Ergo, latency is minimal, power efficiency is high. The satellite doesn't have any idea what the signal means. 2. Decode/retransmit. This you need to RX it, strip the carrier out, demodulate it possibly thousands of channels individually spanning a massive bandwidth, intelligently decide what to do with it while buffering it, mix with one of many new carriers, amplify, retransmit. Latency high, power efficiency low. The latter requires some serious routing power which isn't necessarily available either cost efficiently or reliably of the shelf. Getting something like that which is rad hardened isn't likey to succeed and you can't just launch three redundant core 2's to do it like Dragon. Imagine launching a radiation hardened 4G base station. That's a good analogy.

schiffern 10y ago

> That means routers and intelligence which means uplink, interlink, downlink hops in both directions. 600 ms here we come again. The story from Musk is 20-30 ms latency anywhere on Earth. https://www.youtube.com/watch?v=AHeZHyOnsm4&t=7m00s https://www.youtube.com/watch?v=AHeZHyOnsm4&t=7m00s Fiber has an order of magnitude greater number of hops/routers/repeaters, moves 50% slower, and has to travel more distance to route around continents. See https://news.ycombinator.com/item?id=12984991 https://news.ycombinator.com/item?id=12984991 In the linked video Musk says 4 hops to go from Seattle to South Africa, so they're skipping satellites. It works out that at 1100 km altitude they have vacuum line-of-sight for any satellite within 6000 km ground track in any direction. >I don't know how they're going to ... >Managing that ... hurts my head. It is indeed a Hard Problem. https://www.youtube.com/watch?v=AHeZHyOnsm4&t=5m18s https://www.youtube.com/watch?v=AHeZHyOnsm4&t=5m18s >So it's something that would both provide optionality for people living in advanced economies, as well as people in poor countries that don't even have electricity or fiber or anything like that. So it's a real enabler for people in poor regions of the world and it gives optionality for people in wealthier countries. >So I think it's something that definitely needs to be done. And it's a really difficult technical problem to solve. So that's why we need the smartest engineering talent in the world to solve the problem. >And, you know, at the same time to make sure that we don't create Skynet. So... [laugh] Ironically, the server room at Spacex (jokingly!) was called Skynet. [laugh] Though fate has a great sense of irony, so we really need to make sure that doesn't come true...