[Starlink] "Interesting set of developments with Starlink. Musk says they will support "international aid orgs" in Gaza, Israel now says they will use "all available means" to stop SpaceX from doing so.

[Alexandre Petrescu]

Le 12/11/2023 à 00:47, Ulrich Speidel via Starlink a écrit :
> On 11/11/2023 6:09 pm, Alexandre Petrescu via Starlink wrote:
>>
>> I want to say that I think this hexagon is an imaginative idea of the
>> GUI designer.  I think it does not correspond to reality.  I am not sure
>> about even the most basic fact such as the dimension of the hexagon, or
>> of a more circular 'spot' radius.
> Well it's the basis on which SpaceX will sell you a fixed subscription 
> or not, so it's a bit more than just a GUI designer's fancy.

Thanks, it is good to know.

The satellitemap.space site displays relatively large hexagons, but says 
they are not affiliated with starlink.

The availabaility map published by starlink.com shows hexagons much 
smaller in size.

>>
>> It was the case like that with earlier maps of cellular network
>> deployments.  The name 'cell' itself that comes from it - it's a
>> hexagon, like in a honey pot.  In practice, no cellular network
>> deployment I am aware of has cells of that kind of precise shape. The
>> base stations themselves are not following such precise patterns.   The
>> precise forms of coverage shapes can not be given by operators because
>> it is unique, difficult to calculate, and depends on many landscape
>> factors and other propagation conditions.  What can be given is the type
>> of antennas, their precise placement and orientation.  That is public
>> info of cellular systems in some countries.
>
> Yes, but I wouldn't think of the Starlink hexagons as "cells" in the 
> cellphone sense. In the cellphone sense, you'd have a base station per 
> cell - and some seem to think that Starlink has something like a "spot 
> beam per cell". But that's clearly not what it is.

YEs, I fully agree.


>
> Starlink cells are quite obviously predominantly a tool to control 
> user density on the ground.
> We know well that Dishy orients itself to the area of the sky where it 
> can expect to see the largest number of satellites without falling 
> foul of GSO protection rules where applicable. Dishy then associates 
> with one of them at a time for period that are multiples of 15 second 
> intervals (we know that from the obstruction maps available from Dishy 
> via grpc). We also know that the capacity we get via these 
> associations fluctuates along with the 15 second intervals.
>
> These are all hallmarks of a burst slot based system where each 
> satellite handles a set of time and frequency slots (TDM+FDM), such 
> that a combination of a periodic time slot, a frequency channel and 
> perhaps a number of other parameters (spreading code, polarisation, 
> spatial multiplexing through beamforming at the satellite) defines a 
> channel through which Dishy talks to the satellite or receives from 
> the satellite. This sort of technology has been around for decades 
> (see GSM mobile comms). During your slots, the satellite your Dishy is 
> associated with will project a beam towards you.
>
> Fluctuations in the capacity are a result of a Dishy having more or 
> fewer of these slots assigned during subsequent 15 second intervals. 
> If a satellite picks up more users for the next interval, the number 
> of slots it can make available to your Dishy goes down. If it sheds 
> users as it moves along but you hang on, then you get a few more 
> slots, until either the satellite picks up more user or you change 
> satellite.
>
> For a scheme like this to work, you need to ensure that the number of 
> slots that the visible satellites can offer to their users on the 
> ground works out to an acceptable average minimum number of slots per 
> user at all times. As the number of slots per satellite is likely 
> fixed (at least for the same generation satellite), that puts a limit 
> on the number of users within view on the ground. This is where the 
> hexagons come in - they help ensure that the user density doesn't grow 
> to a level anywhere where a Dishy would struggle to get enough slots.

Sounds as 'beamforming'.  Could be.

>
> I'd presume that the size of the hexagons was chosen to reflect the 
> ability of the beamformers on the satellites to resolve a locality on 
> the ground (no need to go for higher resolution then).

It can make sense.  Whether it is true or not is another matter.

For my part, I think there is a need for a description of that, which 
comes from starlink.  It should tell the sat antenna numbers, positions, 
aperture, orientation.

> I'd also presume that the number of fixed users allowed per hexagon 
> would depend a bit on geographical latitude, visible satellite density 
> and load contributions from a location's surroundings (Colorado 
> farmers would likely see more of those from their neighbours down the 
> road than folks on Rapa Nui). Roaming subscribers aren't guaranteed 
> the same service levels (read: their number of slots is allowed to dip 
> further than those of fixed subscribers), but as they can't be told 
> where to be, SpaceX uses pricing to control user density indirectly.
>
>>
>> With starlink antennas there is no authoritative public info (from
>> starlink) about the precise orientation and types of antennas of the
>> sats.  The reported positions of sats are rather irregular - much more
>> irregular than that precise shape of hexagons shown in the photo.
> Yes - see above.
>>
>> The placement of teleports is also unknown, but speculated by end users.
> In some cases, their locations are precisely known from their spectrum 
> licenses.

That is a question.

For where I live, the spectrum licenses could come from several sources: 
2 country authorities, 1 Europe authority and ITU.

I am trying to look at them, but it is not easy because they differ in 
some respects.

>>
>> The info about satellite tracking, their precise situation: I still need
>> to find out where that info comes from more precisely and how is it
>> obtain (is it reported by sats or is it  other cameras/radars that
>> 'range' each one of them, or is it simply speculated from an initial
>> plan of trajectory; and what is the delay between the actual fact and
>> what is seen on GUI: seconds, minutes or hours delays).
>
> https://celestrak.org/NORAD/elements/index.php

It has a Donate button, which seems to make it a site built by an 
independent end user.  It is a great tool already!   With respect to the 
starlink sats positions: celestrak might simply reflect an original data 
which is made by space-track.org which is a US authority.  Or maybe not, 
they dont say it.  I dont know.

My question is how is the original data on space-track.org (or other 
original source of sat position data) created: do they range the sats 
(i.e. point lasers at them and wait for replies, radar, or similar) or 
do the sats transmit their positions on a voluntary and cooperative basis?

Another question is about which starlink sats are 'in-service' and 
deliver service, and which not?  It is not only a matter of altitude.  
The current websites telling 'in-service' or similar attributes, do not 
seem to be related to starlink, and do not seem to take that data from 
DISHYs.  They seem to be simply telling that if it is at a 550km 
altitude then they're in service.

There is also a question of latency between what is shown on a computer 
screen about the position of a sat, and where it actually is.  For 
example, if I see it now on my screen to be above my head, will I see it 
if I look up?

Alex