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Starlink Maritime

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Re: Starlink Maritime

#481

Post by shaklee3 »

walrus01 wrote: post #423
shaklee3 wrote: post #390

Earlier quoted context omitted.

this is completely incorrect. viasat's technology is far more advanced than starlink. just because it's not LEO doesn't mean it's simple. and starlink doesn't have dramatically increased capacity. they have a moderate increase over the busy areas geo incumbents have. most of their capacity is over water.

The end results of the link budgets required for geostationary to low cost consumer grade terminals means that now matter how good viasat's tech is, the end result is going to be mediocre. Have you actually lived on the far end of a consumer grade highly contended oversubscribed ku/ka band vsat terminal? Viasat's modems and rf chain stuff are about as good as can be expected within the very constrained BOM budget, an…

I've had their service for 4 years straight in the past. it's not as good as cable, but it's nowhere near as bad as you say if you're not playing real time games.

the constrained BOM is the very reason why the terminal cost is reasonable for this business. it's well known that SpaceX is selling the terminal at a huge loss to gather customers in the short term.

Re: Starlink Maritime

#482

Post by [deleted] »

Johnny555 wrote: post #244
aerovistae wrote: post #178

$5000 a month? Who is this for? I'm a little confused. Seems like even the military would be reluctant at that price point, let alone private boat owners who aren't multimillionaires.

While I agree that the military would be unlikely to use this civilian service on warships, it's not because of the price where $5000 would be a rounding error in the operational cost of the ship. I see this more for commercial operators, like the Ferry between Seattle and Victoria BC - they could sell high speed internet for $10/trip and make a profit if they can sell it to 500 passengers/month.

[deleted]

Re: Starlink Maritime

#483

Post by shaklee3 »

mlyle wrote: post #479
shaklee3 wrote: post #401

Earlier quoted context omitted.

it's extremely hard to do at those data rates. if it wasn't there would be existing examples. Facebook tried and failed.

> it's extremely hard to do at those data rates. ? > if it wasn't there would be existing examples. Let's see. NASA downlinked from the moon to the ground, through the atmosphere at OC-12 rates back in 2013-- so about 100x the distance, with the added penalty of traversing the atmosphere. NFIRE did 5.6 gigabit/sec LEO to ground (again through the atmosphere) in 2011-- shorter distances but higher angular rates which…

are you really comparing the moon to the earth with two satellites at much closer distances moving rapidly?

Re: Starlink Maritime

#484

Post by mlyle »

Phlarp wrote: post #379
mlyle wrote: post #182

Earlier quoted context omitted.

It's not that hard of a problem to do fast free-space optical in space within a single orbital shell. The only thing that makes it hard for SpaceX is the relatively small mass and volume budgets on their satellites to do precision pointing with, and that you'd really want each satellite to be able to do multiple links and that's taking up a lot of space.

The laser part seems easy, the targeting part seems hard. I'm imaging some type of gimbal, is there a better way? Also seems likely that if they can find a way to make small sats with the ability to accurately point a laser at another sat, that would have pretty obvious implications to the defense dept. SpaceX is a military contractor after all.

> The laser part seems easy, the targeting part seems hard. I'm imaging some type of gimbal, is there a better way?

Here's the design 101 from base principles:

In practice, you need a big-ish telescope on both ends to control beamspread and to collect light from a big aperture. Aperture is a given based on link budget (and you can trade off power to make the aperture smaller, but halving the aperture diameter on both sides means you'll need 16x the power); if you target F/2 then it'll be twice as long as the aperture. Maybe think about a 6cm aperture and 12cm long telescope for a starting point. This will get you a 6 arcsecond wide beam @ 1000nm.

Then, you need to slew this at pretty fast rates-- perhaps 15 degrees per second for acquisition, and control the pointing within 3 arcseconds while tracking at peak rates of a few degrees per second. Yeek! This pretty quickly takes you towards some kind of direct drive fork mount that is very gimbally-looking.

One bit of fun is that you need to have a lot of bandwidth on your reaction control system on the spacecraft, too-- because when you snap one of these telescopes around, the whole craft is going to want to counterrotate, so the reaction control wheels (and/or other telescopes for links in other directions) will need to react. Feedforward is advised.

Re: Starlink Maritime

#485

Post by mlyle »

shaklee3 wrote: post #483
mlyle wrote: post #479

Earlier quoted context omitted.

> it's extremely hard to do at those data rates. ? > if it wasn't there would be existing examples. Let's see. NASA downlinked from the moon to the ground, through the atmosphere at OC-12 rates back in 2013-- so about 100x the distance, with the added penalty of traversing the atmosphere. NFIRE did 5.6 gigabit/sec LEO to ground (again through the atmosphere) in 2011-- shorter distances but higher angular rates which…

are you really comparing the moon to the earth with two satellites at much closer distances moving rapidly?

> are you really comparing the moon to the earth with two satellites at much closer distances moving rapidly?

I'm comparing to LEO to ground, which has a higher rate of angular movement (e.g. harder to point at) than LEO-to-LEO in the same shell, among other things.

I've built systems that point to sub-arcsecond precision at satellites in LEO. It's not quite an off-the-shelf controls problem (e.g. good luck getting a COTS motion controller to hit-a-fast-moving-target-at-a-chosen-time, rather than follow a track and not care about time) but it's not super hard, either.

Re: Starlink Maritime

#486

Post by shaklee3 »

mlyle wrote: post #485
shaklee3 wrote: post #483

Earlier quoted context omitted.

are you really comparing the moon to the earth with two satellites at much closer distances moving rapidly?

> are you really comparing the moon to the earth with two satellites at much closer distances moving rapidly? I'm comparing to LEO to ground, which has a higher rate of angular movement (e.g. harder to point at) than LEO-to-LEO in the same shell, among other things. I've built systems that point to sub-arcsecond precision at satellites in LEO. It's not quite an off-the-shelf controls problem (e.g. good luck getting a…

you should probably have worked for Facebook a few years back when they threw billions at the problem and couldn't solve it.

Re: Starlink Maritime

#487

Post by mlyle »

shaklee3 wrote: post #486
mlyle wrote: post #485

Earlier quoted context omitted.

> are you really comparing the moon to the earth with two satellites at much closer distances moving rapidly? I'm comparing to LEO to ground, which has a higher rate of angular movement (e.g. harder to point at) than LEO-to-LEO in the same shell, among other things. I've built systems that point to sub-arcsecond precision at satellites in LEO. It's not quite an off-the-shelf controls problem (e.g. good luck getting a…

you should probably have worked for Facebook a few years back when they threw billions at the problem and couldn't solve it.

Citation needed, for Facebook: A) spent billions of dollars on this specific problem (free space optical links in space), and B) couldn't solve it.

Given that there's systems that have successfully flown doing links from GEO to LEO (e.g. high angular rates again), using several year old conservative technology, it's not so bad.

There's a million little details, of course. Just conduction cooling for fast optical transceivers is going to be annoying in space, for instance.

Re: Starlink Maritime

#488

Post by shaklee3 »

mlyle wrote: post #487
shaklee3 wrote: post #486

Earlier quoted context omitted.

you should probably have worked for Facebook a few years back when they threw billions at the problem and couldn't solve it.

Citation needed, for Facebook: A) spent billions of dollars on this specific problem (free space optical links in space), and B) couldn't solve it. Given that there's systems that have successfully flown doing links from GEO to LEO (e.g. high angular rates again), using several year old conservative technology, it's not so bad. There's a million little details, of course. Just conduction cooling for fast optical tran…

SpaceX started a LEO system as ambitious as SpaceX for its time back in 2013. again, GEO to LEO is not LEO to LEO, and is also not moon to earth. there are no successful examples of 20+Gbps between LEO satellites. The million details is why SpaceX has yet to turn them on for production.

Re: Starlink Maritime

#489

Post by shaklee3 »

walrus01 wrote: post #424
shaklee3 wrote: post #398

Earlier quoted context omitted.

which is exactly what starlink will be when it has enough customers. it's already having a slow decline in speeds as the network fills, and it's not even close to capacity in most areas.

If you think that the network engineers running starlink in Redmond are going to walk blindly into the mistakes made in excessively oversubscribed networks by every pre existing geostationary vsat consumer grade service, you must have a very low opinion of their intellect, experience and ability to research the market.

I'm not sure why this has to do with network engineers in Redmond. SpaceX doesn't control the rest of the internet, and they don't have enough POPs (and won't) to hit the latency elon promised. there's a reason why fiber internet is 30ms ping and not 15-20ms.

Re: Starlink Maritime

#490

Post by walrus01 »

shaklee3 wrote: post #481
walrus01 wrote: post #423

Earlier quoted context omitted.

The end results of the link budgets required for geostationary to low cost consumer grade terminals means that now matter how good viasat's tech is, the end result is going to be mediocre. Have you actually lived on the far end of a consumer grade highly contended oversubscribed ku/ka band vsat terminal? Viasat's modems and rf chain stuff are about as good as can be expected within the very constrained BOM budget, an…

I've had their service for 4 years straight in the past. it's not as good as cable, but it's nowhere near as bad as you say if you're not playing real time games. the constrained BOM is the very reason why the terminal cost is reasonable for this business. it's well known that SpaceX is selling the terminal at a huge loss to gather customers in the short term.

Even if viasat's consumer service was handing out high quality steel 1.8 meter elliptical offset ku band dishes with norsat PLL LNBs and 8W BUCs to consumers, the path loss and modulations required would mean that a given section of contended (let's say, 10MHz of a transponder) service to many terminals would still have significantly lower speeds and greater oversubscription to be economically viable compared to what end users see right now on starlink.
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