[Starlink] Starship's 4th flight test was magnificent

[Starlink] Starship's 4th flight test was magnificent

[Dave Taht]

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Seeing the booster land on target was simply amazing.

When they kicked into the Blue Danube, during Starship's coast phase, I
started dancing around the boat. The landing phase was a real nailbiter,
but seeing starlink maintain connectivity through nearly it all of that
plasma was amazing, too. To be massively cheered up about spaceflight, hit
starlink's web site for the video. It is hard to imagine them attempting a
catch of the booster for flight 5, that close to boca chica, but...

But that left questions for me. How much overweight are Starship and the
booster now? How much payload can they actually push to an orbit suitable
for deploying starlink? When will they attempt payloads?

The second set of questions are that the newer, larger Starlink satellites
were designed, oh, 4 years ago? with about 4x the capacity of the existing
ones, and I imagine (and hope) that they have been continually redesigned
with an eye to latency now, as well as capacity. Seeing something like
fq_codel actually make orbit would be a capstone to my career, when I
started off wanting to be an "orbital mechanic"  in the first place but
exited entirely after challenger went down...

Lastly, I couldn't help but imagine small repair robots deploying once in
orbit to get a full view of every tile on starship, and perhaps effect
repairs. Call 'em Hewey, Duey and Louie....

Ad Astra!

-- 
https://www.linkedin.com/feed/update/urn:li:activity:7203400057172180992/
Donations Drive.
Dave Täht CSO, LibreQos

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Re: [Starlink] Starship's 4th flight test was magnificent

[Ulrich Speidel]

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On 10/06/2024 11:50 am, Dave Taht via Starlink wrote:
>
> The second set of questions are that the newer, larger Starlink 
> satellites were designed, oh, 4 years ago? with about 4x the capacity 
> of the existing ones, and I imagine (and hope) that they have been 
> continually redesigned with an eye to latency now, as well as capacity.

What do you actually mean by "capacity" here? We have actual numbers in 
terms of what SpaceX are licensed for for user downlink, and that works 
out to be:

 From a V1 or V1.5:

  * no more than 12 Gb/s into a single cell.
  * no more than 16 Gb/s across all user downlink beams.

 From a V2(mini):

  * no more than 20 Gb/s into a single cell on Ku.
  * no more than 48 Gb/s across all beams licensed for Ku user downlink.
  * no more than 25.2 Gb/s across all beams licensed for Ka user
    downlink into a single cell.
  * no more than 99.2 Gb/s across all beams licensed for Ka user downlink.

Note:

  * The current Dishys don't seem to do Ka, at least going by their FCC
    licenses.
  * In Gen 2 systems, there is no longer an explicit distinction made
    between user and gateway downlinks on at least some beams, so the
    above figures assume that all service downlink beams are carrying
    user traffic.
  * The above figure are before any FEC.
  * The single cell limits are independent of the number of satellites
    you deploy - it's the most a cell can get.

But, like you, I'm somewhat intrigued that we haven't see any follow-up 
applications from SpaceX at the FCC for the 3rd generation. 
SAT-LOA-20200526-00055 is four years old, and its latest amendment from 
March this year (unless something's popped up in the last  few weeks) 
relates to their D2D plans only. The latest amendment pertinent to 
Internet things is from August 2021. The gap between Gen 1 
(SAT-LOA-20170726-00110) and Gen 2 (SAT-LOA-20200526-00055) was just 
over three years - and it took almost that long to get 
SAT-LOA-20170726-00110's last modification SAT-MOD-20200417-00037 filed. 
Maybe now that they know that they can get a lift, they will. Or maybe 
they're going flag of convenience and will launch under the Tongan 
regulator, where they've applied for 29,995 satellites, somewhat more 
recently.

-- 

****************************************************************
Dr. Ulrich Speidel

School of Computer Science

Room 303S.594 (City Campus)

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



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Re: [Starlink] Starship's 4th flight test was magnificent

[Michael Richardson]

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Dave Taht via Starlink <starlink@lists.bufferbloat.net> wrote:
    > When they kicked into the Blue Danube, during Starship's coast phase, I
    > started dancing around the boat. The landing phase was a real
    > nailbiter, but seeing starlink maintain connectivity through nearly it
    > all of that plasma was amazing, too. To be massively cheered up about

Silly legal/technical question:

When starship is in a suborbital, ~140km apogee (coast phase) over Atlantic
Ocean or Africa, whose jurisdiction are the power limits set by?

If at 140km altitude, that's 20% to 30% closer to the satellites than on
land.  OTH, it's moving really fast, and does the hand-off really work?
Are they just using TCP (or maybe QUIC) for data, or something else?

Also, during the entire Tonga situation, Ulrich provided lots of really good
explanation of how hard it was to do a downlink.  That was before the space
lasers.  I would guess that this data link required inter-satellite lasers,
since downlink over oceans (and probably Africa) would be difficult.

    > Lastly, I couldn't help but imagine small repair robots deploying once
    > in orbit to get a full view of every tile on starship, and perhaps
    > effect repairs. Call 'em Hewey, Duey and Louie....

Naw. R2-xx are Astro *MECHS*. https://www.youtube.com/watch?v=gfMoXBOjWBM

--
]               Never tell me the odds!                 | ipv6 mesh networks [
]   Michael Richardson, Sandelman Software Works        |    IoT architect   [
]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on rails    [


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Re: [Starlink] Starship's 4th flight test was magnificent

[David Lang]

Dave Taht wrote:

> But that left questions for me. How much overweight are Starship and the
> booster now? How much payload can they actually push to an orbit suitable
> for deploying starlink? When will they attempt payloads?

According to Elon a couple months ago, the current flying versions could deliver 
~50t to orbit (in reusable mode), they have 3 more block 1 ships left, and the 
block 2 ships will be well over 100t (not counting any benefits from weight 
reduction as they fly them more and can examine them post-recovery)

note that if they flew them in expendable mode, they could at least double that 
payload.

Block 3 ships are a bit further out, they are expecting them to handle 200t in 
fully recoverable mode.

> The second set of questions are that the newer, larger Starlink satellites
> were designed, oh, 4 years ago? with about 4x the capacity of the existing
> ones, and I imagine (and hope) that they have been continually redesigned
> with an eye to latency now, as well as capacity.

the V2 were about 8-10x the capacity of the V1.5 (the ones they could launch 
50-60 per flight), the v2 mini they have been launching (~22/flight) are about 
midway between the two. No recent word on the V2s, but Tim Dodd did another 
starbase visit with Elon before the flight, so watch for that to show up soon.

David Lang

Re: [Starlink] Starship's 4th flight test was magnificent

[Alexandre Petrescu]

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Le 10/06/2024 à 01:50, Dave Taht via Starlink a écrit :
>
> [...] seeing starlink maintain connectivity through nearly it all of 
> that plasma was amazing, too.

I dont understand: the rocket body and head ('starship')  where 
connected to starlink sats during flight?  Wouldnt be enough to transmit 
straight to ground?  Or maybe the entire trajectory is too long too 
distanced from ground receivers?

Alex

> To be massively cheered up about spaceflight, hit starlink's web site 
> for the video. It is hard to imagine them attempting a catch of the 
> booster for flight 5, that close to boca chica, but...
>
> But that left questions for me. How much overweight are Starship and 
> the booster now? How much payload can they actually push to an orbit 
> suitable for deploying starlink? When will they attempt payloads?
>
> The second set of questions are that the newer, larger Starlink 
> satellites were designed, oh, 4 years ago? with about 4x the capacity 
> of the existing ones, and I imagine (and hope) that they have been 
> continually redesigned with an eye to latency now, as well as 
> capacity. Seeing something like fq_codel actually make orbit would be 
> a capstone to my career, when I started off wanting to be an "orbital 
> mechanic"  in the first place but exited entirely after challenger 
> went down...
>
> Lastly, I couldn't help but imagine small repair robots deploying once 
> in orbit to get a full view of every tile on starship, and perhaps 
> effect repairs. Call 'em Hewey, Duey and Louie....
>
> Ad Astra!
>
> -- 
> https://www.linkedin.com/feed/update/urn:li:activity:7203400057172180992/
> Donations Drive.
> Dave Täht CSO, LibreQos
>
> _______________________________________________
> Starlink mailing list
> Starlink@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/starlink

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Re: [Starlink] Starship's 4th flight test was magnificent

[David Lang]

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Alexandre Petrescu wrote:

> Le 10/06/2024 à 01:50, Dave Taht via Starlink a écrit :
>> 
>> [...] seeing starlink maintain connectivity through nearly it all of that 
>> plasma was amazing, too.
>
> I dont understand: the rocket body and head ('starship')  where connected to 
> starlink sats during flight?  Wouldnt be enough to transmit straight to 
> ground?  Or maybe the entire trajectory is too long too distanced from ground 
> receivers?

Yes, unlike other rockets, Starship has multiple starlink dishes on it and has a 
high bandwidth connection through them during it's flight. There are only so 
many ground stations around the world for rockets to talk to directly (and 
especially over the large oceans and Africa there are substantial gaps in 
coverage)

the Starliner flight for example, only had telemetry and audio, no video during 
it's flight. The first Starliner test flight had the capsule misbehaving furing 
one of it's gaps in coverage, which prevented controllers on the ground from 
fixing the problem fast enough to salvage the flight.

Also, during reentry, the plasma tha builds up blocks any radio down to the 
ground, and with anything other than a starlink, it even blocks radios up to 
satellites. A combination of the large size of the Starship, and the Starlink 
capabilities makes it the first rocket that is able to provide live feeds 
throughout the entire reentry.

For this mission, there were some gaps in the coverage, Elon has said they will 
be repositioning the starlink antennas on future flights to eliminate the blind 
spots and get continuous coverage.

The Polaris Dawn private flights are doing experimentation with laser tie-ins to 
the starlink constellations. NASA has the TDRS system to provide near global 
coverage, see this video from Scott Manley on the topic 
https://www.youtube.com/watch?v=42GpWBSwjZM

David Lang

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Re: [Starlink] Starship's 4th flight test was magnificent

[Ulrich Speidel]

On 10/06/2024 2:22 pm, Michael Richardson via Starlink wrote:
> Dave Taht via Starlink <starlink@lists.bufferbloat.net> wrote:
>      > When they kicked into the Blue Danube, during Starship's coast phase, I
>      > started dancing around the boat. The landing phase was a real
>      > nailbiter, but seeing starlink maintain connectivity through nearly it
>      > all of that plasma was amazing, too. To be massively cheered up about
>
> Silly legal/technical question:
>
> When starship is in a suborbital, ~140km apogee (coast phase) over Atlantic
> Ocean or Africa, whose jurisdiction are the power limits set by?

The power limits for transmission are ultimately set by the ITU, to be 
enforced by the authority of whichever state has approved the spacecraft 
(which would be the FCC in this case I guess). But there's a catch or 
five here.

The main power limit is for power hitting the ground (downlink to end 
user), because that might get into the receive antenna of some sort of 
ground based system and wreak havoc there.

In this context it's helpful to understand that interfering signals 
don't have to be on the same frequency that you are trying to receive. A 
transmitter's output might have >99% of its power within the band you 
want it to be in, but the rest distributes across the remainder of the 
spectrum - as a rule of thumb, the closer you are to the "intended" 
frequency with your receiver, the more of those spurious emissions you 
see. These emissions may be a few orders of magnitude below the intended 
signal in power, but because RF communication deals with intended 
signals that can differ by many orders of magnitude, your receiver will 
still hear them - you need the help of distance, antenna directionality 
and in some cases even filters in order to suppress that unwanted signal.

Similarly, receivers aren't just listening on the frequency they're 
tuned to - they're similarly listening on all other frequencies, too, 
except that any signal there needs to be a bit stronger to break 
through. Your cheap car radio will demo that effect to you when driving 
past an FM broadcasting transmitter.

So in the case of the power limits in non-GSO satcom, you have a whole 
raft of microwave receivers on the ground - some pointing skywards - and 
too many to dodge them individually (you'll notice Starlink not being 
offered around radio telescopes - these are super-sensitive and even the 
usual ITU limit is too high there). Moreover, they are approximately the 
same distance as your intended receiver - so whatever you throw at your 
intended receiver, they can snap up as interference.

The opposite case occurs (in principle) when transmitting from the 
ground (or a re-entering spacecraft) to a non-GSO sat above you, with a 
geostationary sat lurking behind your satellite in the distance. In this 
case, the bit of signal beam (think light beam as in car headlights) 
that shines past the non-GSO sat - you could jam that satellite's 
receiver and spoil someone's Superbowl (or worse, Superbowl ads!). This 
is somewhat less critical than the opposite direction, though, mainly 
because you're trying to hit a target that's maybe 1000 km away whereas 
the part of the geostationary orbit that cops the beam leftovers is 
40,000 km or so away. This means that your signal (which suffers 
spherical spreading) is around 40^2=1600 times lower at the 
geostationary sat than at your intended receiver. That's about 33 dB in 
difference, which helps, but then again, the geostationary satellite 
user's uplink suffers the same spread - and may not be aiming at 
producing the same signal level at the satellite antenna as you are 
aiming for on your non-GSO satellite. So there is also a risk here of 
some interference. But in most cases, transmitting up is OK and power is 
more of a matter of what you can afford down on the ground (OK, it's 
more complex than that, but that's for another post).

Now in the case of a video link from a re-entering spacecraft, you get 
the "break" in reception due to signal being absorbed in plasma on 
spacecraft re-entry. That plasma isn't an atmospheric layer, it's simply 
air molecules getting disturbed in their daily business by a spacecraft 
passing by at entirely unreasonable speeds, knocking their electrons 
off. Now that plasma forms wherever the spacecraft grates with the 
atmosphere - read mostly below and around the sides. So what you then 
get is a comet-like "tail" of plasma - a bit like a cone, and there's 
comparatively little plasma inside the cone.

Conventionally, if you had to communicate your re-entry video or audio 
feed to a ground station, you had to communicate *through* that cone's 
wall. Similarly, if you wanted to go "up", you had to go to a TDRSS 
satellite, of which there were only a small number in orbit - and the 
one visible to you would have been on the other side of the plasma cone 
wall with high probability. With Starlink, you have potentially a few 
dozen satellites within field of view, and the chances of having one 
within view out the back of the cone are relatively good (but not 
guaranteed). The other day, they got lucky that the star(link)s lined up ;-)

Quite how that lucky satellite that got to handle the re-entry video 
feed got to downlink it is another question. Splashdown was NW of 
Australia - I don't have an accurate location at this point, but if it 
was close enough to WA, it could have been handled by one of the 
gateways there. Otherwise, the laser ISLs do also a good job at 100 
Gb/s, and it could have come down at a gateway near you...

> If at 140km altitude, that's 20% to 30% closer to the satellites than on
> land.  OTH, it's moving really fast, and does the hand-off really work?
> Are they just using TCP (or maybe QUIC) for data, or something else?
That'll ultimately be their choice, but I suspect it'd be something 
UDP-based off the shelf. Zoom maybe?
>
> Also, during the entire Tonga situation, Ulrich provided lots of really good
> explanation of how hard it was to do a downlink.  That was before the space
> lasers.  I would guess that this data link required inter-satellite lasers,
> since downlink over oceans (and probably Africa) would be difficult.
>
>      > Lastly, I couldn't help but imagine small repair robots deploying once
>      > in orbit to get a full view of every tile on starship, and perhaps
>      > effect repairs. Call 'em Hewey, Duey and Louie....
>
> Naw. R2-xx are Astro *MECHS*. https://www.youtube.com/watch?v=gfMoXBOjWBM
>
> --
> ]               Never tell me the odds!                 | ipv6 mesh networks [
> ]   Michael Richardson, Sandelman Software Works        |    IoT architect   [
> ]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on rails    [
>
>
> _______________________________________________
> Starlink mailing list
> Starlink@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/starlink

-- 
****************************************************************
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/
****************************************************************

Re: [Starlink] Starship's 4th flight test was magnificent

[Ulrich Speidel]

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On 10/06/2024 2:38 pm, David Lang via Starlink wrote:
>
> the V2 were about 8-10x the capacity of the V1.5 (the ones they could 
> launch 50-60 per flight), the v2 mini they have been launching 
> (~22/flight) are about midway between the two. No recent word on the 
> V2s, but Tim Dodd did another starbase visit with Elon before the 
> flight, so watch for that to show up soon.

I think it'd be useful we could agree on what we mean by "capacity" 
before we start throwing numbers around, especially relative ones. For 
Starlink, I can think of the following capacities (yes, plural):

  * User up-/downlink capacity from/to a single user. (How many bits/s
    can I throw at a Dishy?)
  * Downlink capacity to all users in a single cell (under the proviso
    that we don't have any users in adjacent cells that need / want
    service - think small island in the middle of the Pacific).
  * Overall user downlink capacity from a single satellite to multiple
    cells. (Can't deploy co-frequency beams with identical polarisation
    to the same cell if you have multiple such beams on your bird, but
    can do so if we can aim them at different cells)
  * Gateway uplink capacity (to users served directly by the satellite
    or indirectly via ISLs)
  * Gateway downlink (from users served directly by the satellite or
    indirectly via ISLs)
  * Dto. per gateway (see co-frequency beam issue)
  * Processing capacity: Number of bits / s that a satellite can pump
    between its receive beams / incoming ISLs and transmit beams /
    outgoing ISLs.

It's getting late and I probably forgot one or two ;-)


-- 

****************************************************************
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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Re: [Starlink] Starship's 4th flight test was magnificent

[David Lang]

Ulrich Speidel wrote:

> The opposite case occurs (in principle) when transmitting from the 
> ground (or a re-entering spacecraft) to a non-GSO sat above you, with a 
> geostationary sat lurking behind your satellite in the distance. In this 
> case, the bit of signal beam (think light beam as in car headlights) 
> that shines past the non-GSO sat - you could jam that satellite's 
> receiver and spoil someone's Superbowl (or worse, Superbowl ads!). This 
> is somewhat less critical than the opposite direction, though, mainly 
> because you're trying to hit a target that's maybe 1000 km away whereas 
> the part of the geostationary orbit that cops the beam leftovers is 
> 40,000 km or so away. This means that your signal (which suffers 
> spherical spreading) is around 40^2=1600 times lower at the 
> geostationary sat than at your intended receiver. That's about 33 dB in 
> difference, which helps, but then again, the geostationary satellite 
> user's uplink suffers the same spread - and may not be aiming at 
> producing the same signal level at the satellite antenna as you are 
> aiming for on your non-GSO satellite. So there is also a risk here of 
> some interference. But in most cases, transmitting up is OK and power is 
> more of a matter of what you can afford down on the ground (OK, it's 
> more complex than that, but that's for another post).

As I understand it, Starlink does not have ground stations transmit towards the 
geostationary satellites, they only target the starlinks when they are not in 
line to avoid exactly this problem)

> Conventionally, if you had to communicate your re-entry video or audio 
> feed to a ground station, you had to communicate *through* that cone's 
> wall. Similarly, if you wanted to go "up", you had to go to a TDRSS 
> satellite, of which there were only a small number in orbit - and the 
> one visible to you would have been on the other side of the plasma cone 
> wall with high probability. With Starlink, you have potentially a few 
> dozen satellites within field of view, and the chances of having one 
> within view out the back of the cone are relatively good (but not 
> guaranteed). The other day, they got lucky that the star(link)s lined up ;-)

As I underand it, it's not just luck, the Starship is so much larger than 
anything else that the plasma does not just wrap around the craft and close up 
behind it, the sheer size of the craft gives the plasma a chance to cool a bit 
(and you can see that in the videos)

Also, if it was 'luck' then they were lucky on both Starship reentry flights 
(and since the ship was tumbling during flight 3, that would be saying a lot)

David Lang

Re: [Starlink] Starship's 4th flight test was magnificent

[David Lang]

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Ulrich Speidel wrote:

> On 10/06/2024 2:38 pm, David Lang via Starlink wrote:
>> 
>> the V2 were about 8-10x the capacity of the V1.5 (the ones they could 
>> launch 50-60 per flight), the v2 mini they have been launching (~22/flight) 
>> are about midway between the two. No recent word on the V2s, but Tim Dodd 
>> did another starbase visit with Elon before the flight, so watch for that 
>> to show up soon.
>
> I think it'd be useful we could agree on what we mean by "capacity" before we 
> start throwing numbers around, especially relative ones. For Starlink, I can 
> think of the following capacities (yes, plural):
>
> * User up-/downlink capacity from/to a single user. (How many bits/s
>   can I throw at a Dishy?)
> * Downlink capacity to all users in a single cell (under the proviso
>   that we don't have any users in adjacent cells that need / want
>   service - think small island in the middle of the Pacific).
> * Overall user downlink capacity from a single satellite to multiple
>   cells. (Can't deploy co-frequency beams with identical polarisation
>   to the same cell if you have multiple such beams on your bird, but
>   can do so if we can aim them at different cells)
> * Gateway uplink capacity (to users served directly by the satellite
>   or indirectly via ISLs)
> * Gateway downlink (from users served directly by the satellite or
>   indirectly via ISLs)
> * Dto. per gateway (see co-frequency beam issue)
> * Processing capacity: Number of bits / s that a satellite can pump
>   between its receive beams / incoming ISLs and transmit beams /
>   outgoing ISLs.

I believe the numbers thrown around are for the total satellite capability, it's 
not per user or per cell and it includes the in-space laser links.

David Lang

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Re: [Starlink] Starship's 4th flight test was magnificent

[Ulrich Speidel]

On 11/06/2024 12:04 am, David Lang wrote:
> As I understand it, Starlink does not have ground stations transmit 
> towards the geostationary satellites, they only target the starlinks 
> when they are not in line to avoid exactly this problem)
Correct.
>
>> Conventionally, if you had to communicate your re-entry video or 
>> audio feed to a ground station, you had to communicate *through* that 
>> cone's wall. Similarly, if you wanted to go "up", you had to go to a 
>> TDRSS satellite, of which there were only a small number in orbit - 
>> and the one visible to you would have been on the other side of the 
>> plasma cone wall with high probability. With Starlink, you have 
>> potentially a few dozen satellites within field of view, and the 
>> chances of having one within view out the back of the cone are 
>> relatively good (but not guaranteed). The other day, they got lucky 
>> that the star(link)s lined up ;-)
>
> As I underand it, it's not just luck, the Starship is so much larger 
> than anything else that the plasma does not just wrap around the craft 
> and close up behind it, the sheer size of the craft gives the plasma a 
> chance to cool a bit (and you can see that in the videos)
That'll probably help, yes.
>
> Also, if it was 'luck' then they were lucky on both Starship reentry 
> flights (and since the ship was tumbling during flight 3, that would 
> be saying a lot)

I guess the problem is hard to quantify - essentially you have to have a 
Starlink satellite that's within the steering cone of one of the phased 
arrays on Starship AND the path to which doesn't lead through a cone 
wall AND that's been assigned to serve that particular phased array AND 
that needs to work out through handovers to other satellites for your 
entire flight. That's probably possible a large percentage of the time 
given the number of sats about now, but perhaps not 100% (yet), 
especially around tropical latitudes where satellite density is about 
half of what you get in the 30's to mid-50's. And yes I guess they were 
probably lucky in that sense, yes.


-- 
****************************************************************
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/
****************************************************************

Re: [Starlink] Starship's 4th flight test was magnificent

[Ulrich Speidel]

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On 11/06/2024 12:06 am, David Lang wrote:
>
> I believe the numbers thrown around are for the total satellite 
> capability, it's not per user or per cell and it includes the in-space 
> laser links.

But what does this actually mean? Again there you could look at the sum 
of ISL capacities (3 x 100 Gb/s where installed) plus beam capacities 
(version dependent), but that doesn't necessarily mean that the 
satellite can pump between them at full barrel.

Defining a total capacity isn't all that easy when you think of it.

-- 
****************************************************************
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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Re: [Starlink] Starship's 4th flight test was magnificent

[Alexandre Petrescu]

Le 10/06/2024 à 11:49, David Lang a écrit :
> Alexandre Petrescu wrote:
>
>> Le 10/06/2024 à 01:50, Dave Taht via Starlink a écrit :
>>>
>>> [...] seeing starlink maintain connectivity through nearly it all of 
>>> that plasma was amazing, too.
>>
>> I dont understand: the rocket body and head ('starship')  where 
>> connected to starlink sats during flight?  Wouldnt be enough to 
>> transmit straight to ground?  Or maybe the entire trajectory is too 
>> long too distanced from ground receivers?
>
> Yes, unlike other rockets, Starship has multiple starlink dishes on it 
> and has a high bandwidth connection through them during it's flight. 

Thanks, I did not know that.

A rocket using dishes to talk to sats sounds as a difficult means, as 
the rocket might turn around its short axis almost entirely during that 
hyperbolic trajectory (head up then nose down).   But ok, if it works, 
maybe taking advantage from some reflections from ground or other 
things, then all the better for them.

> There are only so many ground stations around the world for rockets to 
> talk to directly (and especially over the large oceans and Africa 
> there are substantial gaps in coverage)
True.
>
> the Starliner flight for example, only had telemetry and audio, no 
> video during it's flight.

yet the space shuttle was streaming videos of its take-off, without 
sats.  It was VGA resolution IIRC.

> The first Starliner test flight had the capsule misbehaving furing one 
> of it's gaps in coverage, which prevented controllers on the ground 
> from fixing the problem fast enough to salvage the flight.
I see, I did not know that.
>
> Also, during reentry, the plasma tha builds up blocks any radio down 
> to the ground, and with anything other than a starlink, it even blocks 
> radios up to satellites.

I did not know they use plasma to propel that rocket.  Actually I dont 
know much about how these things can be propelled, but I know that with 
these high speed objects photos one can see many things like 'aura' or 
'glow'  or even 'glory' in the certain light conditions.  If that is 
'plasma' then that could be it.

> A combination of the large size of the Starship, and the Starlink 
> capabilities makes it the first rocket that is able to provide live 
> feeds throughout the entire reentry.
This looks indeed great.  The time is so short during that flight that 
many things of the communication system have to be set up correctly.
>
> For this mission, there were some gaps in the coverage, Elon has said 
> they will be repositioning the starlink antennas on future flights to 
> eliminate the blind spots and get continuous coverage.

Looking forward to that.

Alex

>
> The Polaris Dawn private flights are doing experimentation with laser 
> tie-ins to the starlink constellations. NASA has the TDRS system to 
> provide near global coverage, see this video from Scott Manley on the 
> topic https://www.youtube.com/watch?v=42GpWBSwjZM
>
> David Lang
>
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Re: [Starlink] Starship's 4th flight test was magnificent

[David Lang]

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Alexandre Petrescu wrote:

>> Also, during reentry, the plasma tha builds up blocks any radio down to the 
>> ground, and with anything other than a starlink, it even blocks radios up 
>> to satellites.
>
> I did not know they use plasma to propel that rocket.  Actually I dont know 
> much about how these things can be propelled, but I know that with these high 
> speed objects photos one can see many things like 'aura' or 'glow'  or even 
> 'glory' in the certain light conditions.  If that is 'plasma' then that could 
> be it.

it's not propelled by plasma, but as it's reentering, the air can't get out of 
the way and gets compressed into plasma. Watch the flight test 3 and 4 videos, 
at about the 45 min mark as it gets down below ~120Km you start to see a glow 
build up. That is the air being compressed into plasma around the ship.

with the typical small capsules, it wraps around the capsule to completely 
encose the capsule and results in zero (or close to it) communications during 
the most dangerous part of the reentry.

The combination of the Starship size and the Starlink capability means that 
these two flights are the only ones in history where we have a real-time feed 
through the hottest parts of the flight. We have recordings from other flights, 
but until they slow down, no way to get the data out of the spacecraft.

David Lang