7 ms·

Do you know why are they doing this? Lower orbit is probably cheaper?

deleted 8y ago
[deleted]
regnerba 8y ago
Cheaper how? I would assume with a lower orbit they experience more drag and deorbit faster meaning they need to be replaced more often. Maybe using the ones in lower orbit to cover more densely populated locations?
- Rebelgecko 8y ago
  The original orbits would take ~100 years to decay, which is way longer than the life of the satellite. The new orbit is around 5 years (not taking into account maneuvers from the fuel on board). Makes a lot of sense, especially since it looks like they'll be iterating the design as they go (two that jumped out at me: initially not all satellites will be taking advantage of both Ku and Ka bands, and not all satellites will have phased array antennas)
  - regnerba 8y ago
    That's really interesting, than you for sharing.
crunchlibrarian 8y ago
Geosynchronous satellite latency in best case: 250ms LEO latency best case: 6ms I've used those Hughes satellite connections before, I never got anything close to 250ms. More like 400ms.
- Diederich 8y ago
  > LEO latency best case: 6ms Light travels about 1800km in 6ms, but that's just one way. Straight up and straight down at 550km is 3.6ms.
  - gameswithgo 8y ago
    light is slower in the atmosphere, did you adjust for that?
    - Rebelgecko 8y ago
      Speed of light in air is still ~0.9997c (and approaches 1 as altitude increases), so it's a much less noticeable difference than it is for copper or glass
- walrus01 8y ago
  The absolute minimum latency you'll ever see with geostationary is about 489ms. That's assuming 1:1 dedicated transponder capacity and something like a higher end SCPC terminal and modem, accounting for latency and modulation/coding/FEC by the satellite modems on both ends. Consumer grade hughesnet stuff will vary anywhere from 495ms in the middle of the night to 1100ms+ during peak periods due to oversubscription.
  - shaklee3 8y ago
    This should probably tell you something about spacex's claims as well. The actual latency is never just the slant range. There's a ton of processing and network switching too.
    - walrus01 8y ago
      I am pretty optimistic about SpaceX's claims for what the space-segment latency will be. If you look at the system architecture for current generation high-bandwidth Ka-band geostationary services, which has dozens of spot beams on North America, there's about 30 teleports spread out around the US and Canada. These allow Viasat and Hughesnet customers, and similar, to consume capacity in the same spot beam as the teleport they're uplinked from (vs the satellite cross-linking a set of kHz from one Ka-band spot beam to another). For example, customers in really rural areas of Wyoming are going to connect to a teleport that's in Cheyenne, which will usually be in the same spot beam. Sites in Cheyenne near the railway have really good terrestrial fiber capacity for an earth station operator to buy N x 10 or 100GbE L2 transport links to the nearest major city. It would be technically possible, but uneconomical and an inefficient use of space segment transponder kHz to have customers in Wyoming moving traffic through a teleport in the Chicago area. Here's an illustration of Ka-band spot beams on a typical state of the art geostationary satellite: http://www.southwestsatelliteinternet.com/images/Ka-band-spot-beams.gif http://www.southwestsatelliteinternet.com/images/Ka-band-spo... Applying the same concept to starlink, telesat's proposed system, and oneweb, if they build a number of teleports geographically distributed near rural areas, it will allow individual satellites to serve as bent-pipe architecture from CPE --> Teleport, within the same moving LEO spot beams, or to have customer traffic take only one hop through space to an adjacent satellite before it hits the trunk link to an earth station. For example customers in a really rural area of north Idaho along US95 might "see" a set of moving satellites that also have visibility to an earth station in Lewiston, ID, where carrier grade terrestrial fiber links are available. Or a customer in a remote mountainous area of eastern Oregon may uplink/downlink through a teleport in Bend. The ultimate capacity of the system will be determined by how few hops through space they can get the traffic to do. Since every satellite will be identical and capable of forming a trunk link to a starlink-operated earth station, when it's overhead of it, they have an incentive to build a large number of earth stations geographically distributed around the world. It's basically the same idea as o3b's architecture but at a much smaller scale.
theptip 8y ago
Low orbit is cheaper to get a satellite to just considering launch costs (less fuel, easier to recover the first stage), but as siblings have mentioned, it's more expensive overall, particularly considering that you need lots more satellites to provide coverage. Their plan to launch O(1000) satellites is to get lower latency and higher bandwidth, which would render the current generation of satellite internet obsolete. It's a great example of the sort of business plan that's only possible with cheap launches that SpaceX's reusable rockets have provided. Here's a more detailed primer: https://arstechnica.com/information-technology/2016/11/spacex-plans-worldwide-satellite-internet-with-low-latency-gigabit-speed/ https://arstechnica.com/information-technology/2016/11/space...
- RivieraKid 8y ago
  What is O(1000) satellites?
  - oh_sigh 8y ago
    It's borrowed from comp sci, but you can read O(x) as "on the order of x", so maybe 900, maybe 1200, but somewhere around there.
    - loeg 8y ago
      In Comp Sci O() notation has a very specific meaning and "on the order of" does not approximate it. I think it was probably just a misuse of the notation.
      - gameswithgo 8y ago
        "The letter O is used because the growth rate of a function is also referred to as the order of the function" order of...order of yeah I know there is no "growth"
        loeg 8y ago
        You've taken an informal and sloppy summary of big-O notation, isolated a single English expression, and construed that a similar English expression used in a different context with entirely different meaning is an accurate approximation of the formal meaning. You would be incorrect.

deleted 8y ago

[deleted]

Cheaper how? I would assume with a lower orbit they experience more drag and deorbit faster meaning they need to be replaced more often. Maybe using the ones in lower orbit to cover more densely populated locations?

Rebelgecko 8y ago
The original orbits would take ~100 years to decay, which is way longer than the life of the satellite. The new orbit is around 5 years (not taking into account maneuvers from the fuel on board). Makes a lot of sense, especially since it looks like they'll be iterating the design as they go (two that jumped out at me: initially not all satellites will be taking advantage of both Ku and Ka bands, and not all satellites will have phased array antennas)
- regnerba 8y ago
  That's really interesting, than you for sharing.

crunchlibrarian 8y ago

Geosynchronous satellite latency in best case: 250ms LEO latency best case: 6ms I've used those Hughes satellite connections before, I never got anything close to 250ms. More like 400ms.

Diederich 8y ago
> LEO latency best case: 6ms Light travels about 1800km in 6ms, but that's just one way. Straight up and straight down at 550km is 3.6ms.
- gameswithgo 8y ago
  light is slower in the atmosphere, did you adjust for that?
  - Rebelgecko 8y ago
    Speed of light in air is still ~0.9997c (and approaches 1 as altitude increases), so it's a much less noticeable difference than it is for copper or glass
walrus01 8y ago
The absolute minimum latency you'll ever see with geostationary is about 489ms. That's assuming 1:1 dedicated transponder capacity and something like a higher end SCPC terminal and modem, accounting for latency and modulation/coding/FEC by the satellite modems on both ends. Consumer grade hughesnet stuff will vary anywhere from 495ms in the middle of the night to 1100ms+ during peak periods due to oversubscription.
- shaklee3 8y ago
  This should probably tell you something about spacex's claims as well. The actual latency is never just the slant range. There's a ton of processing and network switching too.
  - walrus01 8y ago
    I am pretty optimistic about SpaceX's claims for what the space-segment latency will be. If you look at the system architecture for current generation high-bandwidth Ka-band geostationary services, which has dozens of spot beams on North America, there's about 30 teleports spread out around the US and Canada. These allow Viasat and Hughesnet customers, and similar, to consume capacity in the same spot beam as the teleport they're uplinked from (vs the satellite cross-linking a set of kHz from one Ka-band spot beam to another). For example, customers in really rural areas of Wyoming are going to connect to a teleport that's in Cheyenne, which will usually be in the same spot beam. Sites in Cheyenne near the railway have really good terrestrial fiber capacity for an earth station operator to buy N x 10 or 100GbE L2 transport links to the nearest major city. It would be technically possible, but uneconomical and an inefficient use of space segment transponder kHz to have customers in Wyoming moving traffic through a teleport in the Chicago area. Here's an illustration of Ka-band spot beams on a typical state of the art geostationary satellite: http://www.southwestsatelliteinternet.com/images/Ka-band-spot-beams.gif http://www.southwestsatelliteinternet.com/images/Ka-band-spo... Applying the same concept to starlink, telesat's proposed system, and oneweb, if they build a number of teleports geographically distributed near rural areas, it will allow individual satellites to serve as bent-pipe architecture from CPE --> Teleport, within the same moving LEO spot beams, or to have customer traffic take only one hop through space to an adjacent satellite before it hits the trunk link to an earth station. For example customers in a really rural area of north Idaho along US95 might "see" a set of moving satellites that also have visibility to an earth station in Lewiston, ID, where carrier grade terrestrial fiber links are available. Or a customer in a remote mountainous area of eastern Oregon may uplink/downlink through a teleport in Bend. The ultimate capacity of the system will be determined by how few hops through space they can get the traffic to do. Since every satellite will be identical and capable of forming a trunk link to a starlink-operated earth station, when it's overhead of it, they have an incentive to build a large number of earth stations geographically distributed around the world. It's basically the same idea as o3b's architecture but at a much smaller scale.

theptip 8y ago

Low orbit is cheaper to get a satellite to just considering launch costs (less fuel, easier to recover the first stage), but as siblings have mentioned, it's more expensive overall, particularly considering that you need lots more satellites to provide coverage. Their plan to launch O(1000) satellites is to get lower latency and higher bandwidth, which would render the current generation of satellite internet obsolete. It's a great example of the sort of business plan that's only possible with cheap launches that SpaceX's reusable rockets have provided. Here's a more detailed primer: https://arstechnica.com/information-technology/2016/11/spacex-plans-worldwide-satellite-internet-with-low-latency-gigabit-speed/ https://arstechnica.com/information-technology/2016/11/space...

RivieraKid 8y ago
What is O(1000) satellites?
- oh_sigh 8y ago
  It's borrowed from comp sci, but you can read O(x) as "on the order of x", so maybe 900, maybe 1200, but somewhere around there.
  - loeg 8y ago
    In Comp Sci O() notation has a very specific meaning and "on the order of" does not approximate it. I think it was probably just a misuse of the notation.
    - gameswithgo 8y ago
      "The letter O is used because the growth rate of a function is also referred to as the order of the function" order of...order of yeah I know there is no "growth"
      - loeg 8y ago
        You've taken an informal and sloppy summary of big-O notation, isolated a single English expression, and construed that a similar English expression used in a different context with entirely different meaning is an accurate approximation of the formal meaning. You would be incorrect.