Re: [Starlink] Starlink for Tonga?

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

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Update just in from Tonga Cable is that the Reliance cable ship will lay 
at least 55 km of fresh cable. They've spent the last 36 hours or so 
doing three traverses of the cable route around 30 nautical miles west 
of where the cable was broken at the Tongatapu side.

This older post gives a bit of an idea of how the Reliance works:

https://www.reddit.com/r/ThingsCutInHalfPorn/comments/4yttq7/reliance_undersea_cable_laying_repair_ship_te/

On 8/02/2022 9:44 am, Ulrich Speidel wrote:
>
> 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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>>>>
>>>>
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>>>
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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/
> ****************************************************************
>
>
>
-- 
****************************************************************
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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