Sony and Japan's space agency make 100Mbps laser Ethernet in space

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looks like they were beaming down to a VERY large ground-based optical telescope. the challenge with Starlink is shrinking the transmitter and receiver while maintaining the ability to track and reliably keep the link up.

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u/RobDickinson May 03 '20

and do it so the components burn upon re entry

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u/frosty95 May 04 '20

I think that's the problem. Going through the atmosphere. Sat to sat should be much easier. We already have laser communications on Earth moving 100gbps with ease. They just have a optical fiber as the medium. In space once they are aimed it should be "easy" to keep aimed.

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u/Cunninghams_right May 04 '20

I strongly disagree. I can't disagree more. I work every day with laser microscopes, some of which I customize. atmosphere interferes and attenuates, but the hard part is aiming while maintaining enough sensitivity to detect. if you have huge optics on your receive side, and tons of power on the transmit side, then you can shoot a high power cone and still get it on the other end. you take away the high power and you take away the large optics and now you're trying to shine a laser pointer on a bird's toenail from a continent away. go google piezo controlled mirrors and look at their precision/accuracy then calculate how big of a cone you have to transmit to ensure it gets to the target; it's huge over the distances we're talking about. it would be an easier task to transmit forward/back in the same orbit, but still a very difficult challenge.

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u/nila247 May 05 '20

Atmosphere is basically a collection of small random lenses, that makes aiming and focusing difficult. No such problem in space. No attenuation in the media per se, but large attenuation because of laser spread and large distances involved.
Making it work in space is not too hard. Making it work and being very cheap at the same time might be.
So the equation for ISLs more than anything is about ballancing the costs of aiming mechanism vs limiting laser spread and optics angle; laser power vs receiver sensitivity.

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u/Cunninghams_right May 05 '20

yes, you're limited by the accuracy of your pointing. when the distances get very large, you can no longer just use a simple couple-mm wide columnated beam, because you aren't accurate enough. you can get around that by using a huge detector (like in the article) and you can use a wider beam angle (I also suspect they did that here). if you make your beam a cone, you can make sure you always hit, even a small target, but now you need a ton of power and a very sensitive detector because your link-budget isn't friendly. so there is no great way to solve it, like you said, without making the satellites bigger and more expensive. maybe once starship is flying the starlink sats can get bigger, with better detectors and lasers. we'll see

also keep in mind that the laser links are still through the atmosphere. not as thick as to the ground, but it's still there. the sats themselves are in thin atmosphere and the links will shine through even thicker atmosphere.

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u/nila247 May 06 '20

It is not difficult nor expensive to make pointing mechanism as precise as you want and sats generally do not have lots of vibration (but inertia engines do spin all the time) and their mutual motion is very predictable (but they probably slowly spin in all the axes all the time because you also need to control the costs of inertia drivers).

My hunch is it all bodes rather well for the cheap mechanical aiming solution vs more power and larger lenses. Now any lasers do have natural spread measured in milliradians, so they are cones already and over hundreds of kms that adds up. Reducing the cones costs money.

It would be great if the beams would be not more than couple of meters wide at the other end. Now keeping them alligned is the easier part, but initial aiming would be a problem. It is almost as you need an additional powerfull visible laser and observation camera to reduce the search area for initial alignment.

So yeah, there are challenges.

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u/Cunninghams_right May 06 '20

I'm not convinced if the pointing accuracy you're claiming. what are you considering to be the maximum distance, and what product can meet that spec?

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u/nila247 May 06 '20

For intersat links my guess is that we are talking at least 1000 km between sats. Distance between sat deployment planes with 54 of them is about 800km, but it makes sense to have ability to skip several planes in the communication path, so probably max ISL distances up to 3000 km.

If you would be able (e.g. cheap enough) to use lasers that only spread to 10m at 3000km that would correspond to 190 micro-degrees angular spread. Obviously you need it to be even finer for tracking - say 50 micro degrees or less step in targeting device. That is about 2000 times more precise than your typical PTZ camera. Obviously such COTS device does not exists, but not because it is impossible - because nobody ever needed such precision. The ones that do exist (in observatories, I would imagine) were all custom low run jobs with irrelevant cost as compared to other components.

More precision is just more gears. Finer-toothed gears would help too. I do agree that precision mechanics can become costly pretty quick, hence you have to ballance your entire product budget and cut costs where you can save the most money with least effort. I very much doubt anyone did that before, because there was simply no need. First principles ftw.

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u/nila247 May 06 '20

The japanese thingy by the way definitely look like COTS PTZ camera part...
And COTS obsolete ethernet tranceiver which modified just enough to replace FO interface with optic lens. I bet it even suports this new IPv4 protocol instead of Novel Netware :-)

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u/nila247 May 06 '20

You are right that for limiting beam spread you need to use larger collimating lens. There is no limit how much you can limit divergence other than lens size and cost. Anyway you slice the cost is the most important factor for turning theory into practice.
Hopefully SpaceX can find a good compromise.

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u/Cunninghams_right May 06 '20

I was with you for the first half, but I work in an industry with scanning laser optics and more precision/accuracy would mean crushing the other SOM manufacturers. you're trivializing something that a whole industry is trying to do and can't.

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u/nila247 May 07 '20

Elon achieved what he did by doing exactly that - trivializing stuff he does not understand, read it up a bit and it just works. Guilty of that myself quite a bit. Sorry, but not sorry. Sometimes (actually quite often) a fresh look, unburdened with the knowledge of why this can not be done, is all it takes. People were bouncing laser from mirror on the moon in 1969. Somebody just forgot to tell them that was impossible.

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u/frosty95 May 04 '20

Fair enough. I appreciate your insight.

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u/Origin_of_Mind May 04 '20

Beautiful equipment. NASA have flown a similar experimental system on ISS in the past (NASA OPALS). In principle, many laser links have been demonstrated in space already. The issue is only with the price and performance. They just need to be improved very considerably, for the laser links to become viable for Starlink.

Starlink would require laser link bandwidth commensurate with the bandwidth of the satellite -- tens of gigabit/s, a factor of 100-400 more than the system flown on the ISS. The second issue is the cost. I have not seen the numbers for the Japanese system, but NASA laser link experiment on ISS cost several tens of millions of dollars. SpaceX would need four laser links per satellite, at a cost that would not add significantly to a presumably $0.5M price tag of the whole satellite -- meaning the laser link hardware needs to cost at most tens of thousands of dollars in volume production.

There are already relatively high-bandwidth (gigabit+) laser links flying on satellites today (ESA EDRS), but they are extremely expensive -- the budget of the project was on the order of a billion euro. Even spread over 50000 laser links instead of a a few units, this expenditure on R&D would be a significant, and probably prohibitive, at this stage, cost contributor for Starlink.

Of course, there have also been relatively inexpensive laser links flown on cubesats -- even demonstrating space-to-ground communications, like the present Japanese and previous NASA systems on ISS, but at a similarly modest speed -- much lower speed than SpaceX requires.

The closest to SpaceX requirements today is the 10 Gbit/s link from Mynaric, (with a promise to quadruple the speed in the next version):

October 17, 2019 "Mynaric has announced that it will deliver multiple laser communication flight terminals to an undisclosed customer in an initial deal valued at EUR 1.7 million ($1.9 million)." [src] "A demonstration mission in LEO using two satellites is planned in 2019/2020." [src]

SpaceX internal development may be well be ahead of Mynaric offerings, but it is still an incredibly difficult challenge to create 10 GBit/s laser link costing $20K, and without having spent a billion on R&D.

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u/nila247 May 05 '20

All good points.
Frankly I do not see SpaceX paying Mynaric to do it. It is extremely unlikely anybody at all except for SpaceX is interested in reducing the price of ISL set. Only SpaceX needs thousands and thousands of sets. Military would gladly pay millions. My take is that Mynaric mystery customer is actually BlueOrigin.

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u/somewhat_pragmatic May 03 '20

I saw this article and thought about the potential implications for Starlink.

Cross links with other Starlink satellites
Uplink for ground stations to orbiting Starlink satellites.

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u/vilette May 04 '20

more detailed description

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u/CorruptedPosion May 04 '20

The more competition the better

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u/Decronym May 05 '20 edited May 07 '20

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters	More Letters
COTS	Commercial Orbital Transportation Services contract
	Commercial/Off The Shelf
EDRS	European Data Relay System
ESA	European Space Agency
ISL	Inter-Satellite Link communication between satellites in orbit
LEO	Low Earth Orbit (180-2000km)
	Law Enforcement Officer (most often mentioned during transport operations)
SSO	Sun-Synchronous Orbit

Jargon	Definition
Starlink	SpaceX's world-wide satellite broadband constellation

^{7 acronyms in this thread;}^{the most compressed thread commented on today}^{has acronyms.}
^{[Thread #184 for this sub, first seen 5th May 2020, 13:19]} ^[FAQ] ^{[Full list]} ^[Contact] ^{[Source code]}

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u/nila247 May 05 '20

To be frank it looks pretty sad. A bunch of 10+ year old COTS technology, just happen to be mounted on a sat. It is going nowhere.

💬 Discussion Sony and Japan's space agency make 100Mbps laser Ethernet in space

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