On Sat, 8 Apr 2023, Ulrich Speidel wrote:
On 8/04/2023 12:10 am, David Lang wrote:
I will note that in the Starlink plans, there are plans
to put a layer of satellites at a sigificantly lower altitude.
I should add to this that this would seem like a good strategy, except of
course that this comes with its own set of challenges. Earth observation
satellites in particular are abundant in lower orbits - if you have a camera
on board, you want to be as close to your subject as you can. So there isn't
quite as much space down there as there is further up.
Residual atmospheric drag at lower altitudes is also higher, which means you
either need to take more fuel to compensate (=heavier satellite & fewer sats
per launch) or you need to replace the satellites more often.
You also need more satellites for global coverage in a shell like this.
Also, as you mostly look at satellites sideways when you're a ground station,
the path length and therefore the path loss isn't necessarily all that much
lower - going from 550 km to 275 km gives you an extra 6 dB of gain if the
satellite is straight overhead, but that advantage shrinks as you move away
from zenith.
the published plan is a shell at ~340km (7500 satellites) in addition to the one
at ~550km (and a possible 'long haul' shell at ~750km with <1k satellites)
By launching 10x as many satellites, and each one being able to handle 10x
the data, they _may_ get to 100x, but that is really going to be pushing it.
(note that this is for ~10x the number of satellites lauched by everyone
other than SpaceX since Sputnik)
Having seen figures of ~45k sats bandied around for some proposed
mega-constellations, the 10x number of satellites might just work out.
regulatory approval required, but starlink is aiming for ~42k satellites, they
are only approved for somewhere around 10-12k so far and I believe they are
nearing 4k in orbit.
Whether we'll get to 10x the capacity per satellite is another question
altogether given spectral constraints.
yes, to get to this sort of capacity, you need to have multiple satellites
covering each cell at a given time, which per the research published not that
long ago was not yet the case.
With ISLs, one could in principle free
up part of the gateway traffic spectrum by putting gateways in areas that are
devoid of other users, but quite how practical that is given that remote
areas are where LEOs will be needed most is a good question.
supporting terminal-to-terminal traffic also opens interesting possibilities
(although less than we would like due to the server-centric nature of current
Internet usage)
One option that could push things a little further in conjunction with LEOs
would be HAPSÂ - high altitude platform systems, essentially solar-powered
UAVs that act as stratospheric cell towers with tours of duty measured in
weeks or months. These could use lasers as backhaul to LEO networks, yet
project comparatively narrow phased array beams to users on the ground. A
HAPS flying at 30 km overhead has a path loss that's around 25 dB below that
of a LEO sat at 550 km, and a clear optical path to the satellites above.
Technology isn't quite there yet - essentially, we're at the point where
solar cells have become performant enough in conjunction with batteries that
have become light enough to allow sustainable cyclic recharging of a UAV's
flight systems. But there are still issues to be addressed around the excess
power required to operate a cell site in the sky and or course all the
regulatory and safety aspects associated with operating things that don't
burn up when they come down.
Google shuttered project Loon (balloons to do this rather than UAVs) in the last
year or two
If you can get fiber, it's always going to be better than a wireless option,
DSL is threatened by Starlink in many suburbs, cablemodems depend so much on
the ISP it's hard to say
This is an interesting comment. Completely agree on the fibre aspect.
DSL I think is threatened more by fibre than Starlink in most places (except
the US perhaps), which has basically displaced most DSL connections where it
became available. We were on DSL here till 2017, and as fibre was on the
horizon for a while, the company that runs the cable network here on behalf
of the telcos stopped investing in new DSLAM modules, instead preferring to
switch customers with problematic ones to modules that had become available
as a result of customers migrating to fibre. We found ourselves with a weird
problem literally overnight one day - intermittent disconnects lasting a
minute or two. These persisted through a change of DSL router, and logging
these for a few days showed a clear diurnal peak time pattern - so it was
obvious we were dealing with DSLAM-side crosstalk issues here. I asked to be
switched to a different DSLAM. This was an odyssee of support calls given
that you cannot call the lines folk directly - you must call your retail ISP,
who pays someone in India a few rupees to tell you to reboot your router to
make the problem go away. By the time I'd educated their 3rd tier support
about what crosstalk was, I'd literally spent many many hours on the phone to
India. Eventually, they switched me over to a new DSLAM and the problem went
away for a few months, just to return as they kept rewiring more legacy
customers.
when I switched from cablemodem to 129k SDSL in 2002, my usable bandwidth
significantly improved.
For those who still have DSL now, VDSL plans start at less than half of what
Starlink charges, with potentially comparable data rates, so not everyone
will want to switch.
I live in the greater LA area, in the middle of a town of >125k The best DSL I
can get takes two phone lines to give me 8m down 1m up (in theory I should get
10/2 but the line quality doesn't support it), and this costs me significantly
more than starlink does.
Where I see uptake of Starlink in urban areas here is by (a) geeks and (b)
folk who want a (secondary) connection that is independent of local telcos
that run inane call centres in India.
As more people work from home, just having a secondary connection becomes more
important.
Cable TV and cable modems are of course pretty much unheard of here - are
there any cable modems / ISPs that do more than a few dozen Mb/s down?
yes, cable modems can push 1G. I have one at 600/30 (but as a business line with
static IP addresses, it costs me about triple the starlink connection)
David Lang
_______________________________________________
Starlink mailing list
[email protected]
https://lists.bufferbloat.net/listinfo/starlink
