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> Interesting. I didn't know that coverage was limited. I assumed satellite == pretty much all of earth. The low orbits that give Starlink its low latency comp

by wolrah 4y ago

> Interesting. I didn't know that coverage was limited. I assumed satellite == pretty much all of earth. The low orbits that give Starlink its low latency compared to geostationary satellite internet services also mean that each satellite can only see a small part of the earth at any given time. This is why they need so many satellites to provide reliable coverage. Right now each satellite has to communicate directly to a uplink station, so it's only possible to provide coverage to areas where a satellite can simultaneously see the user and the uplink. This is where SpaceX's planned inter-satellite link capability comes in to play, they claim they will be able to use lasers in a free-space optical network (think fiber without the fiber) to relay data directly from satellite to satellite, allowing service more than a single hop from a uplink station. This will also hypothetically allow for direct user to user connections over the satellite network that do not traverse the terrestrial internet, which would be huge for both military and business applications. Lots of words have been written about intercontinental high frequency trading for example. Supposedly every satellite launched in 2022 has the capability but as far as I'm aware it hasn't been openly demonstrated to work yet. Making it work reliably within a single orbital ring is a hard problem and the claimed ability to cross-connect between adjacent rings is an absurdly hard problem. Neither are impossible, but I'll believe it when I see it.

Phlarp 4y ago
>I'll believe it when I see it. This whole "yea inter-sat free space fiber links are totally going to happen" charade smacks of the same hype baiting as "full self driving by end of year" nonsense that Elon has been spouting since 2018. The Starlink "team" did an AMA on reddit[0] last year and it was comical how empty the answers were. People asked about the space lasers and the answers were all "yea it's a really hard problem, BTW we're hiring!" which honestly felt like an admission from HR that they're looking for engineers willing/able to cash the checks marketing already wrote. [0] https://www.reddit.com/r/Starlink/comments/jzozv3/every_answer_from_the_starlink_team_ama/ https://www.reddit.com/r/Starlink/comments/jzozv3/every_answ...
- mlyle 4y ago
  It's not that hard of a problem to do fast free-space optical in space within a single orbital shell. The only thing that makes it hard for SpaceX is the relatively small mass and volume budgets on their satellites to do precision pointing with, and that you'd really want each satellite to be able to do multiple links and that's taking up a lot of space.
  - Phlarp 4y ago
    The laser part seems easy, the targeting part seems hard. I'm imaging some type of gimbal, is there a better way? Also seems likely that if they can find a way to make small sats with the ability to accurately point a laser at another sat, that would have pretty obvious implications to the defense dept. SpaceX is a military contractor after all.
    - mlyle 4y ago
      > The laser part seems easy, the targeting part seems hard. I'm imaging some type of gimbal, is there a better way? Here's the design 101 from base principles: In practice, you need a big-ish telescope on both ends to control beamspread and to collect light from a big aperture. Aperture is a given based on link budget (and you can trade off power to make the aperture smaller, but halving the aperture diameter on both sides means you'll need 16x the power); if you target F/2 then it'll be twice as long as the aperture. Maybe think about a 6cm aperture and 12cm long telescope for a starting point. This will get you a 6 arcsecond wide beam @ 1000nm. Then, you need to slew this at pretty fast rates-- perhaps 15 degrees per second for acquisition, and control the pointing within 3 arcseconds while tracking at peak rates of a few degrees per second. Yeek! This pretty quickly takes you towards some kind of direct drive fork mount that is very gimbally-looking. One bit of fun is that you need to have a lot of bandwidth on your reaction control system on the spacecraft, too-- because when you snap one of these telescopes around, the whole craft is going to want to counterrotate, so the reaction control wheels (and/or other telescopes for links in other directions) will need to react. Feedforward is advised.
      - 4y ago
intrasight 4y ago
> Supposedly every satellite launched in 2022 has the capability Additionally there's the issue that their operating licenses don't allow inter-satellite communications.
- wolrah 4y ago
  > Additionally there's the issue that their operating licenses don't allow inter-satellite communications. This is of course a much easier problem to solve than putting a dynamic mesh network in space.
maccam94 4y ago
> as far as I'm aware it hasn't been openly demonstrated to work yet They did a test in late 2020[0], and all launches since June 2021 have been Starlink v1.5 with lasers[1]. 0: https://wccftech.com/spacex-starlink-satellite-laser-test/ https://wccftech.com/spacex-starlink-satellite-laser-test/ 1: https://en.wikipedia.org/wiki/List_of_Starlink_launches https://en.wikipedia.org/wiki/List_of_Starlink_launches
- wolrah 4y ago
  What I mean by openly demonstrated to work is some sort of public demo that would require use of the inter-satellite links. The linked article just says they've started testing and been able to move data, which means nothing about how well it actually works. I'd even be satisfied by specific claims of test results that could be validated once the capability is officially activated.

by wolrah 4y ago

Phlarp 4y ago

>I'll believe it when I see it. This whole "yea inter-sat free space fiber links are totally going to happen" charade smacks of the same hype baiting as "full self driving by end of year" nonsense that Elon has been spouting since 2018. The Starlink "team" did an AMA on reddit[0] last year and it was comical how empty the answers were. People asked about the space lasers and the answers were all "yea it's a really hard problem, BTW we're hiring!" which honestly felt like an admission from HR that they're looking for engineers willing/able to cash the checks marketing already wrote. [0] https://www.reddit.com/r/Starlink/comments/jzozv3/every_answer_from_the_starlink_team_ama/ https://www.reddit.com/r/Starlink/comments/jzozv3/every_answ...

mlyle 4y ago
It's not that hard of a problem to do fast free-space optical in space within a single orbital shell. The only thing that makes it hard for SpaceX is the relatively small mass and volume budgets on their satellites to do precision pointing with, and that you'd really want each satellite to be able to do multiple links and that's taking up a lot of space.
- Phlarp 4y ago
  The laser part seems easy, the targeting part seems hard. I'm imaging some type of gimbal, is there a better way? Also seems likely that if they can find a way to make small sats with the ability to accurately point a laser at another sat, that would have pretty obvious implications to the defense dept. SpaceX is a military contractor after all.
  - mlyle 4y ago
    > The laser part seems easy, the targeting part seems hard. I'm imaging some type of gimbal, is there a better way? Here's the design 101 from base principles: In practice, you need a big-ish telescope on both ends to control beamspread and to collect light from a big aperture. Aperture is a given based on link budget (and you can trade off power to make the aperture smaller, but halving the aperture diameter on both sides means you'll need 16x the power); if you target F/2 then it'll be twice as long as the aperture. Maybe think about a 6cm aperture and 12cm long telescope for a starting point. This will get you a 6 arcsecond wide beam @ 1000nm. Then, you need to slew this at pretty fast rates-- perhaps 15 degrees per second for acquisition, and control the pointing within 3 arcseconds while tracking at peak rates of a few degrees per second. Yeek! This pretty quickly takes you towards some kind of direct drive fork mount that is very gimbally-looking. One bit of fun is that you need to have a lot of bandwidth on your reaction control system on the spacecraft, too-- because when you snap one of these telescopes around, the whole craft is going to want to counterrotate, so the reaction control wheels (and/or other telescopes for links in other directions) will need to react. Feedforward is advised.
    - 4y ago

intrasight 4y ago

> Supposedly every satellite launched in 2022 has the capability Additionally there's the issue that their operating licenses don't allow inter-satellite communications.

wolrah 4y ago
> Additionally there's the issue that their operating licenses don't allow inter-satellite communications. This is of course a much easier problem to solve than putting a dynamic mesh network in space.

maccam94 4y ago

> as far as I'm aware it hasn't been openly demonstrated to work yet They did a test in late 2020[0], and all launches since June 2021 have been Starlink v1.5 with lasers[1]. 0: https://wccftech.com/spacex-starlink-satellite-laser-test/ https://wccftech.com/spacex-starlink-satellite-laser-test/ 1: https://en.wikipedia.org/wiki/List_of_Starlink_launches https://en.wikipedia.org/wiki/List_of_Starlink_launches

wolrah 4y ago
What I mean by openly demonstrated to work is some sort of public demo that would require use of the inter-satellite links. The linked article just says they've started testing and been able to move data, which means nothing about how well it actually works. I'd even be satisfied by specific claims of test results that could be validated once the capability is officially activated.