Re: [Starlink] a puzzling starlink uplink trace

[David Lang <david@lang.hm>]

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satellites below the allocated orbital shells are in transit, either going up or 
coming down. It takes a LOT of energy to change the orbital altitude.

anything at 70km is in the process of re-entering (at launch they are still on 
the rocket at that altitude), so if you are getting reports of satellites being 
operational at that altitude, your source of reports is faulty.

David Lang

  On Thu, 31 Aug 
2023, Alexandre Petrescu via Starlink wrote:

> Date: Thu, 31 Aug 2023 11:13:07 +0200
> From: Alexandre Petrescu via Starlink <starlink@lists.bufferbloat.net>
> Reply-To: Alexandre Petrescu <alexandre.petrescu@gmail.com>
> To: starlink@lists.bufferbloat.net
> Subject: Re: [Starlink] a puzzling starlink uplink trace
> 
> to clarify: I some times look with satmap.space and with n2yo.com at sat 
> altitudes.
>
> Some times I see some starlink sats at lower altitudes than LEO (some 
> times at 70km).
>
> Right now I see sat STARLINK-6065 at 360 km altitude, which is way below 
> LEO and typical 550km altitude of starlink sats.
>
> https://www.n2yo.com/satellite/?s=56812
>
> If these altitude reports are correct, then I think it is hard to say 
> Starlink is anymore simply a LEO constellation.  It is much lower than that.
>
> Further, if the 20ms latency report is due to that 365 km altitude then 
> it is very easy to imagine what lower altitudes would give.
>
> If one reports a great ms latency then it would be great to tell which 
> sat at which altitude was there above at that timestamp.
>
> Alex
>
> Le 31/08/2023 à 10:56, Alexandre Petrescu via Starlink a écrit :
>>
>> Le 30/08/2023 à 20:07, Dave Taht via Starlink a écrit :
>>> In the attached 5 minute plot from a few days ago (I can supply the
>>> flent.gz files if anyone wants them), I see a puzzling spike at T+155s
>>> to nearly 90ms of baseline latency, then down to 20ms.
>>
>> 20ms?
>>
>> A latency of 20ms might come if these low altitude starlink sats (70km 
>> or so) pass by there?
>>
>> Or maybe I dont see quite well these sat altitudes.
>>
>> Alex
>>
>>
>>>   No degree of
>>> orbital mechanics can apply to this change, even factoring in an over
>>> the horizon connection, routing packets on the ground through LA to
>>> seattle, and back, or using a couple ISLs, can make this add up for
>>> me. A combination of all that, kind of does make sense.
>>>
>>> The trace otherwise shows the sawtooth pattern of a single tcp flow ,
>>> a loss (sometimes catastrophic) at every downward bandwidth change.
>>>
>>> An assumption I have long been making is the latency staircase effect
>>> (see T+170) forward is achieving the best encoding rate at the
>>> distance then seen, the distance growing and the encoding rate falling
>>> in distinct steps, with a fixed amount of buffering, until finally
>>> that sat starts falling out of range, and it choses another at T+240s.
>>>
>>> But jeeze, a 70ms baseline latency swing? What gives?  I imagine
>>> somehow correlating this with a mpls enabled traceroute might begin to
>>> make some sense of it, correlated by orbital positions....
>>>
>>>
>>>
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