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.
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_answ...
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/
I'd even be satisfied by specific claims of test results that could be validated once the capability is officially activated.
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.
6900km from the center of Earth. Figure you don't want the link to point within 150km (6500km) of Earth, to not pass through much atmosphere and to not see too much atmospheric glow (even with narrow filters, this matters).
Effectively you have an isosceles triangle with 6900km on the common side and an altitude of 6500km (tangent to "top of atmosphere" at 150km.
sqrt((6900^2 - 6500^2)) * 2 =~ 4600km
One interesting side-effect of the laser links is that they can open up connections between stock exchanges and trading houses that are faster than direct fiberoptic lines. Milliseconds count in high frequency trading.
So I think it's plausible for intercontinental links.
