Re: [Starlink] Starlink for Tonga?

[Ulrich Speidel <ulrich@cs.auckland.ac.nz>]

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https://matangitonga.to/2022/02/08/tonga-cable-broken

On 8/02/2022 9:38 am, Ulrich Speidel wrote:
>
> I've been watching (and commenting on) this ever since one of our MPs 
> tweeted Elon Musk with a plea for help for Tonga (and as the PhD 
> supervisor of Tonga's first PhD student in Computer Science and 
> someone who has had Pacific connectivity at the core of his work, I've 
> got a fairly good understanding of what "Tonga offline" means in 
> practice). That said...
>
> - Practical range from gateway ground station to user ground station 
> is more like 300-400 km. Fiji-Tongatapu is twice that distance.
> - Countless images of gateways (and fencing around it) suggest that 
> satellite elevation from gateways needs to be a bit more than 25deg.
> - Satellite density in the tropics is lowest for Starlink's currently 
> operational 53 degree inclination network.
> - It's my understanding that dishys don't actually track using their 
> motors, which they use only to position themselves initially in the 
> direction of the highest satellite density (=wherever your closest 
> 53rd parallel is, basically). That's a strategy that doesn't really 
> work in the tropics because you can't see the sky above the 53rd 
> parallel. So here, your dishys would need to know to point 
> west-north-west.
>
> While it's encouraging to see Starlink send folk to Fiji to scout 
> things out (there are plenty of Fijian outlying islands where Starlink 
> service would be welcome, too, at least by the locals, not necessarily 
> by the regulators), I don't hold my breath on them making serious 
> inroads when it comes to alleviating the current connectivity crisis.
>
> The cable ship (CS SubCom Reliance) tasked with repair of the cable is 
> on site and, judging by its AIS track, has located the end of the 
> cable coming from Tongatapu. It appears to have shifted a significant 
> distance south (around 1-2 km), possibly as a result of a turbidite 
> flow (underwater landslide) from a seamount in the area that was 
> triggered by the eruption at Hunga further north (my going theory 
> anyway - there's a seamount right where it needs to be for that sort 
> of damage and there's no other event that explains the timing of the 
> cable outage). Either way, if the area is suitable for re-laying the 
> cable, Tonga should be back online within the next week. Otherwise add 
> a week or two.
>
> On 8/02/2022 8:06 am, Nathan Owens wrote:
>> You can simulate it on starlink.sx 
>> <http://starlink.sx>, 
>> maybe Mike will chime in with what he found in doing that.
>>
>> On Mon, Feb 7, 2022 at 11:05 AM Christian von der Ropp <cvdr@vdr.net> 
>> wrote:
>>
>>     But in practice the satellites won't be sitting and waiting at
>>     the edge of this 940km radius. They are moving in and out the
>>     radius and the question is if satellite density is high enough so
>>     that once the serving satellite loses its gateway link there's
>>     another satellite in the 940km radius which also covers Tonga.
>>     And then this new satellite cannot be within certain elevation
>>     angles (~60-80° at 0° azimuth) where the geostationary arc
>>     crosses Fijian skies and the gateway antennas have to seize
>>     emission. My gut feeling is that availability in Tonga would be
>>     <90% simply because it's too far out at the edge of a Fijian
>>     gateway's range where there will be frequent service interruptions.
>>
>>
>>     Am 07.02.2022 um 19:51 schrieb Nathan Owens:
>>>     The current coverage radius of a gateway/ground station with a
>>>     25 degree minimum elevation is ~940km, so nothing in theory.
>>>
>>>     On Mon, Feb 7, 2022 at 10:50 AM Daniel AJ Sokolov
>>>     <daniel@sokolov.eu.org> wrote:
>>>
>>>         Hello,
>>>
>>>         I hope this is not offtopic: Starlink wants to build a
>>>         ground station on
>>>         Fiji to supply Tonga with internet.
>>>
>>>         The distance between Tonga and Fiji is about 750 km minimum.
>>>         That's
>>>         quite the distance.
>>>
>>>         What does Starlink have to do to make this work?
>>>
>>>         Cheers
>>>         Daniel
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> -- 
> ****************************************************************
> Dr. Ulrich Speidel
>
> School of Computer Science
>
> Room 303S.594 (City Campus)
> Ph: (+64-9)-373-7599 ext. 85282
>
> The University of Auckland
> ulrich@cs.auckland.ac.nz  
> http://www.cs.auckland.ac.nz/~ulrich/
> ****************************************************************
>
>
>
-- 
****************************************************************
Dr. Ulrich Speidel

School of Computer Science

Room 303S.594 (City Campus)
Ph: (+64-9)-373-7599 ext. 85282

The University of Auckland
ulrich@cs.auckland.ac.nz  
http://www.cs.auckland.ac.nz/~ulrich/
****************************************************************



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