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Starlink's laser system is beaming 42 petabytes of data per day

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Re: Starlink's laser system is beaming 42 petabytes of data per day

#221

Post by [deleted] »

FpUser wrote: post #218
ortusdux wrote: post #11

Earlier quoted context omitted.

> “Another really fun fact is that we held a link all the way down to 122 kilometers while we were de-orbiting a satellite,” he said. “And we were able to downstream the video.” > For the future, SpaceX plans on expanding its laser system so that it can be ported and installed on third-party satellites. The company has also explored beaming the satellite lasers directly to terminals on the Earth’s surface to deliver…

So what happens to the laser beam when there are clouds?

[deleted]

Re: Starlink's laser system is beaming 42 petabytes of data per day

#224

Post by mr_toad »

wolverine876 wrote: post #199
burnished wrote: post #176

Earlier quoted context omitted.

That doesn't seem right, why would they be bright?

That's a very good question. I'm sure of what I've seen, many times over years: I can tell you that they look like stars - so much that I need a reference point, an actual star or planet, to verify they are moving and not a 'stationary' star (judging movement being otherwise very difficult at that distance). They move very steadily, horizon to horizon, or as far as I can track them. A wild guess, based on memory, is…

> Asteroid? That seems hard to believe, due to size and illumination.

And the distance - most asteroids pass by much further out than even the moon, so their motion would be hard to detect.

Re: Starlink's laser system is beaming 42 petabytes of data per day

#225

Post by mrb »

So that is "432 Mbit/s per laser, and 9000 lasers total". I don't know you guys but I find that statement much more relatable than "42 PB/day". Interestingly, they also say each laser "can sustain a 100Gbps connection per link" (although another part of the article even claims 200 Gbit/s). That means each laser is grossly underused on average, at 0.432% of its maximum capacity. Which makes sense since 100 Gbit/s is probably achievable in ideal situations (eg. 2 satellites very close to each other), so these laser links are used in bursts and the link stays established only for a few tens of seconds or minutes, until the satellites move away and no longer are within line of sight of each other.

And with 2.3M customers, that's an average 1.7 Mbit/s per customer, or 550 GB per customer per month, which is kinda high. The average American internet user probably consumes less than 100 GB/month. (HN readers are probably outliers; I consume about 1 TB/month).

Re: Starlink's laser system is beaming 42 petabytes of data per day

#226

Post by m4rtink »

oconnor663 wrote: post #155
aetherspawn wrote: post #139

Earlier quoted context omitted.

If someone makes a mistake and the satellite deorbits in the wrong place, am I likely to be impaled by a satellite screw or something travelling at terminal velocity?

No, they burn up. You can think of how much work goes into the heat shields on spacecraft that are supposed to survive reentry. Satellites have none of that.

Starlinks are actually built so that nothing sizeable remains at all after reentry. This even delayed the laser coms a bit, as the original laser mirrors were too sturdy & so pieces of them could theoretically make it through.

Re: Starlink's laser system is beaming 42 petabytes of data per day

#228

Post by londons_explore »

nomel wrote: post #182
sephamorr wrote: post #57

Earlier quoted context omitted.

Take a look at the slides from the presentation, I think the geometry clearly shows cross-plane links in the mesh. Having worked on these types of systems, I've had more difficulty with the lookahead angles (rx from where the target was, tx to where it will be due to speed of light) than the tracking -- fine tracking performance was required for all modes, and it largely became a GNC and acquisition time issue (since…

In general , how is the initial alignment performed? Is there rough pointing, followed by some rastering, until the sensor gets a hit? Maybe with some slight beam widening first? My assumption is that you would want exactly one laser, one sensor module, and probably a fixed lens on each? Is the sensor something like a 2x2 array, or pie with three pieces, to allow alignment? Or is it one big sensor that uses perturb a…

A laser that transmits data at 100Gbps can also transmit at 1 bit per second with an additional path loss of 110 decibels.

You'd normally achieve this by transmitting a well-known pseudorandom sequence. You also need clock stability into the ppb range.

A path loss of 110 decibels is huge. It can easily account for your lenses being hugely off axis.

Re: Starlink's laser system is beaming 42 petabytes of data per day

#229

Post by m4rtink »

streb-lo wrote: post #136
latchkey wrote: post #110

Earlier quoted context omitted.

To me, they look like little white dots moving across the sky. Brightness can change as they move too. It'll start off bright and then as it goes away it eventually disappears entirely. Since I usually sit in the same position in the hot tub, I've come to notice that I usually see one of them cross a pretty specific path from north to south, so I've gotten used to looking in that part of the sky as I'm sitting there.…

Just throwing this out there, but has anyone else seen 'formations' of satellites? I've only seen them once but there were about 5 to 10 (it was a while ago) of what I'm assuming are satellites moving in a line formation at high speeds across the night sky. They're too distant and too fast to be planes so I'm assuming they are some sort of military formation of satellites?

I saw ISS in formation with visiting spacecraft a couple times - once with Space Shuttle back in the day and at least once with Dragon. Looks pretty interesting. :)

Re: Starlink's laser system is beaming 42 petabytes of data per day

#230

Post by calrain »

ble wrote: post #5

My understanding of the state of the art of inter-satellite optical links is that they have only been used between satellites that are basically in the same orbital plane and in more or less the same orbit. That is, the angle from one satellite to the other changes very very slowly, so that the optics don't have to do much tracking -- and consequently satellites can only form an optical link with other satellites tha…

I'll assume there is a lot of double/triple (or higher) accounting going on here as data is sent through multiple relay hops to get the intended target.
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