Lasers enable satellite internet backbone, might remove need for deep-sea cables
techxplore.com
techxplore.com
The amount of data going through fibres is absolutely staggering, replacing this with intersatellite links is just not going to happen. First you still need fibre to connect your ground stations (and you need quite a bit of redundancy due to weather) and there are still a lot of unsolved problems (tracking and pointing for example). However there are many interesting applications of optical satellite links and quite a few players are investing in it, the big one is actually data connections for scientific space missions.
The Z on ETHZ is important, ETH on its own is just (loosely) "university", the Z makes it the Zürich one ;D. There is exactly one other: EPFL in Lausanne. (And you can technically call them EPFZ and ETHL if you really want to confuse people.)
(EPF [École Polytechnique Fédérale] is just the French version of German ETH [Eidgenössische Technische Hochschule]. Funnily enough both have pretty good international reputations, but due to the primary regional language being different are rarely recognized to be the same type of Swiss education entity.)
(I mean, it's not super important to understand these two are related, but honestly I feel like it makes them even more impressive. ETHZ already has a MIT-like reputation, with EPFL not far behind. The Swiss are clearly doing something right with their technical universities. And it's a 100% quota too, these two are the only ETHs/EPFs.)
(… to be fair, yes, "Fédérale" translates to "eidgenössisch" when the source is known to be Swiss French / fr_CH, but still. Oh the joys of locale details and translating natural language…)
For extremely latency sensitive applications, I guess they will (e.g. for trading and real-time communications), but for everything else that can wait a few more milliseconds, I'd guess that the operational overhead and reduced reliability will never be worth it, especially if fiber already exists on the same path.
Each submarine cable is 12+ strands which are DWDM multiplexed to 20-40 channels at 100-400gbps.
The entire _planned_ starlink constellation has less aggregate switching capacity than a pair of current generation core routers. The market for terrestrial ethernet _routed_ 400Gbps ports is 10k+ annually and 800Gbps is just getting warmed up.
Satellite is not going to even make the slightest dent in terrestrial networking. Starlink isn't even viable without most of the traffic doing two leg ground-satellite-ground for SP-network connected ground stations. 100% of that traffic is landing on the terrestrial internet.
If you assume a pessimistic 100x over subscription and 50% waste over oceans and non serviced countries * 50mbps (upload + download) * 1.5 million customers that’s well over 1.5 TBPs current capacity for customers which then doubles when you include their base stations. And they that’s today when the current 3887 Satilites which mostly v1.0 and v1.5 which have dramatically less individual bandwidth than v2.0.
PS: Also your port estimate overstates total bandwidth as each point to point link requires a port on each side, and packets generally make multiple hops through the internet.
Total estimate for a “fully deployed” Starlink network is therefore 600 Tbit/s from my pessimistic estimate (or half that if your thinking in terms of customer bandwidth vs traffic handled by the network)
A more realistic estimate is more like 3,000 TBPs as lower density areas can offer higher bandwidth per customer a village of 100 in the Sahara gets the same bandwidth as a town of 100,000 in the US. How much of that actually gets used is a different story.
PS: Individual switches can handle a surprisingly large percentage of total internet bandwidth as packets travel through many of them. 100 switches / average of 4 hops per packet has 25x the bandwidth of a single switch.
And nevermind that Starlink will run out of ground station / inter-satellite link capacity long before reaching the theoretical maximum.
> The entire _planned_ starlink constellation has less aggregate switching capacity than a pair of current generation core routers.
I generally agree with those estimates based on how they’re defining limits though those definitions really depend on what you care about. Aka predicting actual utilization at one end vs just considering what the satellites could physically do in ideal conditions etc. Thus the theoretical impact of direct customer to customer links for a satellite over the Atlantic for example can vary wildly.
Moreover, with a very tiny exception over antarctica or open ocean, every single packet forwarded by starlink is hitting a terrestrial link after a single ground-space-ground hop.
Nobody is going to be making backbones out of Starlink or anything that looks like Starlink. Only the people who know nothing about modern networking performance think otherwise.
Also, Starlink customer to Starlink customer is very compelling for may applications. Undersea cables for example can create much higher latency between areas than their physical separation for example Australia to Madagascar. Similarly there’s still quite a bit of point to point microwave tower connections etc that can now be cheaply replaced.
For it to be really viable as a backbone it would need to be able to do several 100 Gbit/s from one location and that Starlink cannot do (or is built to do). A single satellite has less than 100Gbit/s of RF capacity and you will only have a couple visible above you at any one time. And after that bottleneck comes the inter-satellite link capacity bottleneck which is less than half of that if the information I have found is correct (4 links à 10Gbit/s). I don't think they will be able to sell more than 10 GBit/s service to anyone and that only in not so populated areas.
A single datacenter can reach low Tbit/s of connectivity _alone_ _today_. I don't see how it could make any dent whatsoever in the backbone market.
The other usecases are a different discussion and not as dependent on very high bandwidth numbers.
First data centers very wildly in size and have connections to multiple networks for redundancy, Starlink would be very appealing from that standpoint. Also you’re underestimating bandwidth here, V2 mini are ~80Gbps full V2 weigh 2.5x as much and presumably the bandwidth difference is even higher, but they aren’t launching hardware yet so it’s unclear. Any given location several satellites above it at the current density, at 42,000 you’re talking 50+. Plus if it’s data center to Starlink customer then you’re effectively replacing a Starlink ground station so they might make such installations very cheap.
Starlink doesn't have nice overview of actual specs of future satellites, so I can only use what people have figured out or what they have published. But you are right about the number of satellites, I looked at the wrong column (it was for phase 1 and not 3), so density will indeed be much higher, so from that perspective it will be somewhat more capable (depending on fast/slow their rollout is). And it's not clear if it would actually be cheaper for SpaceX to have such customers (since some of the traffic would go to the rest of the internet - requiring ground station resources) or go elsewhere on the planet (filling up inter-satellite capacity), but that's not too much different from how regular ISPs have to plan (some customers are cheaper for them than others).
I agree, but look up global IP traffic numbers it’s just crossed 1 Pbit recently and that’s across the globe. No individual router needs to handle anything that close to 1 Pbit today, though modular designs would let you manufacture such a router.
Being able to pump 40 terabits per second up to a satellite from a single uplink, as they hope, is significant-- exceeding most subocean cables.
Lines have one biiiiig advantage. They're very easy to monitor(liveness), very hard to imperceptibly tap anymore, they don't move once you put them down (generally), and if they do, you know just where to start looking.
The telescopes involved in this are strongly directional, so whomever is tampering would need to be rather close to the real uplink.
a single cable system under construction(which we are buying part of) (there are over 30) has over 120t of capacity @400G waves, but we are already discussing doing 800G waves, which will double that. We currently operate on over 7 submarine cables, one of the landing stations we operate out of has over 10 cable landing which is over 850T of capacity across all cables.
Most of my metro DF backhaul can push 16-19T down a single pair, and most of my builds are 1728 core fiber.
Starlink is very cool, it will connect ALOT of under served or simply not served people across the world, but the notion that it will even have the slightest chance at dinting the Subsea cable market is laughable.
No, a single uplink can't replace a subsea cable.
This is not real.
Granted. More path loss, dispersion, potential for interference. The question is how well can you do?
> This is not real.
I believe ETHZ; of course there's more to do to make a practical system.
Fiber slows down Berlin <-> NYC by a lot. I usually use Wolfram Alpha for this and it's like 30ms fiber vs. 21ms vacuum.
So in theory starling could offer less hops and better latency. The detour to space isn't that bad either, ~1100km on a 6500km route, and fiber will need some extra hops and detours too.
How much latency is added by routing and switching on a typical transatlantic journey?
And a followup, are there any promising developments for moving the networking infrastructure fully to light as a carrier signal without any electron-based hardware in between?
There aren't too many common natural disasters that could take out a huge fraction of undersea cables in one go.
https://archmeregreenarch.org/1456/news/starlink-and-the-ris...
There is a newer version of fiber optic cable that uses a hollow core. Testing has shown it transmits signals at nearly the speed of light. It is very difficult to produce at scale and will require a generational shift to deploy.
https://sniperinmahwah.wordpress.com/2018/05/07/shortwave-tr...
https://www.sec.gov/files/07feb18_hu_iex_becoming_an_exchang...
"The reduction in trading costs (spreads) is broadly consistent with recent theories on how speed advantages may be used to exploit mechanical arbitrage opportunities. These theories suggest that market makers face adverse selection from fast traders even in the absence of traditional “fundamental” informed trading. For instance, Budish et al. (2015) defnes “quote sniping” as the mechanical arbitrage of taking “stale” quotes before market makers can cancel. In his Comment Letter on IEX’s Exchange Application, Eric Budish argues that IEX’s speed bump may be able to mitigate quote sniping as it allows IEX’s pegged orders to avoid executing against market orders at stale prices.7 Moreover, cross-sectional di˙erences in spreads in response to IEX’s protected quote are consistent with recent theory suggesting that exchange speed is a double-edged sword for market makers (Menkveld and Zoican, 2016). On one hand, faster exchanges allow market makers to update their quotes faster, reducing spreads. On the other hand, higher exchange speed results in a higher probability of quote sniping. Hence, the results support this more nuanced view of the net e˙ects of speed on trading costs. "
Everyone gets the same treatment. Everyone is delayed the same amount.
See https://spectrum.ieee.org/wall-street-tries-shortwave-radio-...
Photonic bandgap / Bragg fiber is being produced in quantity, and some subsea cables are using it.
I'm pretty sure it's the satellite lasers that require the generational shift. One subsea cable has no bearing on any other; once the first is installed, you're up and running. not so with laser-connected swarms.
Judging from [1], lasers are used not for inter-satellite links, but for downstream or upstream links - from satellites to the ground.
Intersatellite links require precise machinery, such as picometer-precise positioning systems [2].
[2] https://www.pi-usa.us/fileadmin/user_upload/pi_us/files/prod...
Also, there should be compensation for satellite rotation, initial targeting and tracking. At ~12km between satellites (~4000 on 550 km orbit), the (possible) target of laser signal receiver which, say, is one meter in diameter will be one third of an angular minute. It is not impossible to target that initially, but keep in mind that laser beam is very focused and its power drops significantly with the angular distance.
I really do not know how to even target satellites' receivers initially, let alone compensate for rotation and track these targets afterwards.
"Space lasers allow Starlink satellites to connect directly to one another, eliminating the need for a local ground station and enabling Starlink. to deliver service to some of the most remote locations in the world - like Antarctica."
AFAIK the satellites within an orbital plane are stationary relative to each other, so once the laser is aimed it should stay connected.
We probably see these fibres for links between the exchange and data centres first (although there it is difficult to beat RF links, as they are direct line of sight)
HFT changes these "beliefs in company" to "beliefs that the stock will go up", and the timeframe of those "beliefs" is sometimes in milliseconds. This turns classic "investment" into a computer game with a lot of real money.
It would take a heavier hand to push against this problem. I'm all for it, I'm just not clever enough or knowledgeable enough to know what would be a good regulation that would fly in congress.
One attempt is the exchange IEX [0] which introduced a ~350 microsecond delay to everything simply by running incoming order data through a ~60km loop of fiber-optic cable.
Perhaps not the most, er, featureful solution, but it's very easy to audit and argue that there are no biases or backdoors.
Iex also offers a variety of (dark) order types that can pull back without the 350us delay if iex believes the incoming flow will be toxic
IANATrader, but I don't think that's entirely true. Yes, it won't stop Carol from getting information from somewhere and then running in front of Alice to the same exchange. [0]
However even fixed-delays [1] can still create uncertainty about what price your order may actually execute at when it hits the server, which is something HFTs rely on more heavily than other traders, since their strategy depends on high-certainty that they will have a small positive margin on every trade.
__
[0] I find it geeky-amusing to write (i.e. IEX) or (ex: IEX) because it feels like the start of a mental tounge-twister.
[1] Can't edit my original post anymore, but apparently there's another 350μs on the outbound path too.
This is also true on every single other exchange, albeit to a smaller degree. You have a larger queue of possible things that may have happened, but this issue exists everywhere. No exchange has instant entry.
On a very short timescale things are very jumpy - nothing happens for a while, and then everything happens all at once. The queuing problem tends to be more of “did another hft beat me to the same event”, not general random other events, so queues like IEXs tend to be emptyish anyways.
Compute all you want, whenever you want, but instead of millisecond timings, optimize stuff for at least some time.
Maybe even a tax on stock profits, which is really high and falls after some time of ownership of such stock (we have this in slovenia, but it's not really high in the first place, and time brackets go less than 5 years (25%), 5-10 years (15%), 10-15 years (10%) , 15-20 years (5%), and zero tax after that.
https://www.brookings.edu/opinions/congress-wants-to-tax-sto...
I wonder what happened to it.
Hong Kong has an FTT of 0.13% currently, it was 0.1% from 1993-2021 so you can compare HFT impacts on these markets. Or compare dozens of other countries with similar rates, Switzerland, Taiwan, France, Italy, Japan.
I haven't thought about this enough, but one thing I'd note is that HFT is risk-taking, and taking a risk generally has the possibility of profit or loss.
A second thing would be that the phrase "society's resources" is a bit dangerous, as it might let us think that the money they're using is somehow everyone's money. When in fact they're spending their money on this, hoping to make a profit.
From the perspective of the whole economy it is everyone's money. Rent seeking behavior is a dead weight loss due to market inefficiency. Through tax policy the incentives can change and largely remove this inefficiency.
Minimum time between buying and selling the same ticker
Mandatory network 'speed bump' of a few ms between the exchange and any trading parties
I was pretty skeptical too, but the more I look into it, the more it just boils down to market making (providing liquidity) and arbitrage (improving price quality across exchanges).
There might be dirty tricks there too – I'm only speaking for legal trading practices here. And if an HFT makes its profit using illegal methods, what's the difference between that and other financial crimes like insider trading, collusion to frontrunning etc.?
I don't really get the (to me somewhat irrational/uninformed) focus on HFTs, when things like payment for order flow probably "siphons off" just as much from retail investors' trades.
I don't think this is generally true. Stock trading isn't charity, it's done to make a profit. Almost trading is done on the basis of second order effects, and has been for as long as there's been a stock market. Stocks aren't given value by the company being profitable, they're given value by what other people are willing to pay for them (okay, yes, dividends also factor in, but many companies don't pay dividends and people still assign value to those stocks).
The honest answer is probably nothing.
As far as I can tell, it neither benefits us, nor costs us. It siphons off a tiny fraction of money, too small to notice, but large enough in aggregate. Some parasite gets to survive, which is annoying if you look directly at it, but ignorable if you don't.
Not at all. If you, for whatever reason, need to sell right now, putting in a market order in an illiquid market can cost you a lot.
It can be discussed how big the contribution of HFTs to market making really is (large companies or exchanges often employ dedicated market makers, I believe?), but the benefit of market making itself should hopefully be obvious.
If the HFTs only trade when the market is already made (or will certainly be, milliseconds later) then they're not really adding any liquidity. They're just doubling the liquidity which was already sufficient.
Are high frequency traders trading in illiquid markets?
That would be surprising to me, it's not high frequency if it's not high volume, and you open yourself up to larger bid/ask spreads.
I think that's only true for IPO shares which often aren't available to retail investors/gamblers like me.
Not quite: By buying shares in a company, you positively influence its share price, which reduces cost of capital for the company (in case it needs it).
Arguably, the difference in impact (in terms of enabling/steering companies to do things) between the IPO and secondary market these days is probably negligible compared to any two single private funding rounds.
It would be slightly amusing to see some sort of HFT ban, only to see people speedrun re-inventing HFT as numerous problems unfold, like dad putting in a market order for AAPL on a day it had a VWAP of $185 and having his trade execute at an average price of $690. Or more serious problems like shortages and surpluses of commodities in different locations due to bad price information.
The only meaningful way to limit the efficacy of these modern trading styles would be purposeful market friction through minimum holding times, circuit breakers, etc. You can't just legislate that people mustnt have low ping.. it's impossible to enforce. And those market friction mechanisms can create scary market conditions like backlogs, etc and guess what, enable market making brokerages to do internal swaps etc. in spite of the friction and essentially be the only ones able to bypass restrictions.
HFT does very similar things, except it's even more opaque to those not doing it. Large financial firms and exchanges sell their order data to HFTs. If you're interested in a deeper dive on what they're doing, a book like Flash Boys will explain how there's a lot more going on than just a quicker network connection.
So I occasionally try to think of a reason to have a guaranteed delay due to signal propagation delay to/from Mars. Would there be a use for putting an automated exchange there? Maybe, but then whomever gates the orders could monitor and predict what will happen 40 minutes out or whatever. Need TLS from trader to exchange or something.
Most of this is improvable with software. As other commenters point out, the resistance is from incumbent trading institutions who have a lot invested in the status quo.
What is an order cancellation? Would different legs on a hedge count as a cancellation?
The closing window is a massive challenge as well. It would have to be accurate down to the nano second and you can bet the exchange is going to get litigated against depending on which bucket the order ends up in.
If you set up mandatory delays per client you would have each hedge funds split up into hundreds of shell companies to get around it.
Having worked at exchanges, most surveillance and analysis of trades happen after the close of day. You’re proposing a literal real-time surveillance system that would be absolutely massive in scale.
> The closing window is a massive challenge as well. It would have to be accurate down to the nano second.
It wouldn't have to be - one could even say first second is for bids, second second there are no bids but a delay to give auction results mid-second and allow people to process.
> the exchanges would know
They can be forbidden to sell that info real-time by their regulator (it arguably would be market abuse and that could be made explicit).
It is definitely not impossible like you are trying to imply. (Financial markets participant with 20 years in the market here, for what it's worth.)
What you're proposing is actually not a ban on HFT, it's a ban on investment strategies other than value investing. How would you implement that in practice? Have every investor swear under oath that they do believe in the company's inherent value, regardless of the rest of the market's behavior?
> HFT goes against the original ethos of a market open to all.
What "original ethos" is that? And even if it existed, wouldn't excluding certain investors go against it much more?
And for the how, just limit the number of transactions one can do per second or the money one can exchange per second. Then everyone will have to be smart instead of being the one with the best connection. Or split the markets in "Joe invests" market and "Bigcorp" invests.
Whatever scheme is defined as "stock exchange" can surely be fixed by another scheme. Humans have been inventing games and agreed to rules for centuries, it's not like it's something we can't do.
No, this is the part most everyone gets wrong about HFT. These systems make money off of volume, not price. They don't care if the price is going up or down. All they care about is that they can capture a small price delta by facilitating a trade faster than someone else and they are willing to do so for smaller fractions of a cent which makes them more attractive to all market participants, including you and your retirement funds. Their concerns are orthogonal to investors and they compete with other HFT firms and market makers.
Proponents argue that HFT and other such innovations provide liquidity to markets; my skeptical take is that this is a nice technical-sounding term for traders with cash to lowball falling asset prices.
1. You could put a limit order at 185$ or lower. But maybe no one is putting a sell order at this price? So you are stuck waiting for some time, maybe never if the price keeps going up? 2. You could put it at 190$ to trigger a trade but you risk buying 5$ more than what you originally wanted if people already cleaned up the book from 185$ to 190$.
The only reason you can definitively say that an apple stock is worth exactly 185$ right now is liquidity/depth of the market. Because there are enough players in the game that is willing to make miniscule amount of profit in very short amount of time.
None of this prevents you from investing using whatever long-term paradigm you prefer. The effects of HFT on that investment style are negligible.
Apple should go up in price slightly, because someone (me) just made a big bet that it's going to do well. The market does this automatically.
TSMC should also go up in price very slightly, because Apple doing well makes it more likely that TSMC (a major vendor of theirs) will also do well, and the market just learned that Apple is slightly more likely to do well, so it also just learned that TSMC is more likely to do well. In other words the companies performance is correlated, so the stock prices should be as well.
By my understanding HFT is the mechanism by which the market can make TSMC go up slightly as well. High frequency traders can react to the information that apple is going to do better (as per it's increased stock price) and buy a bit of TSMC.
This seems like it should make the market more accurate, and if you buy that the market accurately assigning values to a company is a good thing, seems like a good thing.
Anything they do to cram bandwidth into their laser link can reasonably also be applied to fiber optical cables. Except the fiber optical cables come in bundles of 12 to 144 with absolutely no separation issues. Replicating that over open space (air or vacuum), if reasonably possible at all, will chug significant amounts of power in signal processing at the receive end.
There are major benefits to free-space optics -
- quicker to build
- lower latency
- in some cases, large coverage
But deep-sea cables compete on bandwidth, and that's not something free-space optics can beat them on. Why diminish this research achievement by conflating it with that? :(
So, yet again I have to ask because all of the useless answers received to this point have not been an actual answer to what a proper cloud is that could interfere with a signal
If sounds like you don't agree with him, but don't pretend you don't understand him. Please.
Normal ground to satellite communication use wavelengths of 7 mm and up, as those have reasonable cloud penetration.
This is peanuts compared to under sea cables and issues you will find penetrating atmosphere and increasingly, space.
We should keep under sea cables and work on additional connections to make our networks more resilient, both to natural phenomena, equipment failures and sabotage.
I think you're understating the risks from geomagnetic storms. In comparison to satellites, fiber optic cables seem like they'd be relatively unaffected even if the equipment attached to them needs replacement.
But you are right that transoceanic cables need powered repeaters.
> https://en.wikipedia.org/wiki/Boeing_X-37
Russia has already demonstrated its satellite destroying tech:
> https://www.cnbc.com/video/2021/11/16/russia-blows-up-satell...
I haven't said that we should only focus on sea cables, I said that we should do both so that the overall reliability and resiliency increases.
It is basically automatic MAD (Mutually Assured Destruction) out there in space.
implementing the same infra, but using lasers as the backbone could speed up a large area of the country, make rolling out dense radio networks like 5g way faster and cheaper, etc.
If nothing else I could see governments insisting on both just for strategic reasons. Both techs are vulnerable to being fk'd with so doubling up makes sense
The part that impresses me most is they're talking about LEO satellites. Those move fast! Starlink does this with a very impressive phased array antenna design. Conceptually tracking a moving satellite with a laser is as easy as rotating a mirror, not sure how hard it is in practice.
50 Mbps is great consumer bandwidth where?
Where I used to live, I had 2 options for internet access. A Wireless ISP that uses a parabolic antenna pointed at a water-tower about ~20km from my home; or a cell-phone based internet connection.
The WISP allowed me on average 300kb/s transmissions. The Cell-Phone allowed me between 1.5Mb/s and 7Mb/s (to a max use of 5GB/month).
So 50Mb/s is an incredible upgrade.
But sure let's fill up space with junk because North America can't get their shit together and just deploy fiber.
Starlink in practice is 10-200Mbps. Here's their specifications: https://www.starlink.com/legal/documents/DOC-1138-34130-60
An advertised "50 Mbps" mobile connection is dog food if you are used to 50 Mbps fiber. You are lucky if you get 20 Mbps through, though it can be much less. Worst part is all the packet loss that cause inconsistent latency and speed.
Anything that allows video communication/streaming is "great" imho, it certainly is more than enough for most people.
Starlink is already working on a backhaul from satellite to satellite. Interestingly, they claim that they can speed up data transfers by 50% over long distances. Musk said that in a Tweet which I cannot find now. I looked a bit into it and the reason seems to be that light trough a cable can only reach 70% of the speed of light while lasers through the vacuum of space can reach the speed of light.
Multiple satellites. The ISS can see about a thousand miles in each direction to the horizon, so you'd only need to bounce across a couple to cross the Atlantic.
You would send to a satellite in view; my orbital dynamics are poor, but I think with the LEO orbits, you may need to relay in space for a cross ocean link, as it seems unlikely one satelite would have a view of both sides. But Telstar 1 and 2 were used for cross-Atlantic microwave relay with a single satellite in view at a time. Future Telstars were geostationary, because satellite tracking was a lot of work (and with only two satellites, service was intermittent as they were only in view for a portion of their orbits). I imagine satellite tracking for lasers is going to be very difficult as well.
They are already providing service over open ocean out of reach of one hop to base station.
They use a special laser that gives the photons a bit of topspin.
All you need is a well-placed black hole in Earth’s atmosphere.
This gives me negative confidence in the claim
While this experiment has demonstrated that it is possible to compensate for the turbulence of the air, there is no solution for the attenuation caused by bad weather.
It might be possible to use lasers between a base station and satellites only if the base station is located at high altitude in a dry place, like those typically chosen for astronomical observatories, so that the links will be blocked by bad weather only infrequently.
So I do not believe that there is even a remote chance of replacing most undersea cables.
First, in order to enable global communication you need a constellation and good constellation management. This requires fewer spacecraft if you are in GEO, but GEO spacecraft tend to be larger and more expensive.
Second, lasers draw a lot of power. Most is waste heat as far as the spacecraft is concerned, but this can become a problem if the duty cycle is high. High power means much larger arrays, and for a LEO constellation, serious eclipse challenges.
Finally and most importantly, pointing is a challenge. Maintaining pointing control in space is hard, and lasers require much greater accuracy as compared to RF. With RF, the lobes are relatively large and allow some play when it comes to downlink to ground. Lasers are unforgiving.
I’ve led several spacecraft missions with lasercom terminals, and every time it has made development markedly more challenging. I think it will be quite a while before it is mainstream, and certainly before it replaces fiber.
My primary concern comes down to reliably. Your ground station must now accurately target moving satellites, negotiate handoffs, and reroute when necessary. Architecturally, you will need to develop the ground station with at least three transponders: an A link, B link, and a redundant Z link. The A and B take turns localizing to their satellite where one is only allowed to move positions if the other is currently active. The backup Z link is on standby in case of failure or maintenance. The three would likely rotate roles periodically to keep time on each of the motors more evenly distributed amongst them. This system must work in harmony with all the satellites in its network. The satellite system has its own maintenance burden too, including orbital decay requiring you to periodically adjust its position until it runs out of propellant, and send more up when it’s reached the end of its useful life. To me, this is a ton of moving parts.
An undersea cable by contrast, will pretty much be maintenance free once laid only requiring infrequent repairs in the event of a wayward ship anchor. Yes, the data center components will need to upgraded periodically but you don’t need to replace the transmission mode. There are no moving parts, no need To track objects hundreds of miles away, just sending light down a tube.
Is this tech cool? Absolutely. Will it replace undersea cables? Probably not soon, but I can see this as a great solution to link remote islands where it does not make strategic sense to run a cable, or where it is difficult or uneconomical to run a terrestrial connection.
the article says they direct the laser using a MEMS device. not dissimilar to the micromirror arrays used in DLPs for decades, i would assume. you’ve definitely got options that don’t require stepper motors or any macroscopic moving parts here.
I wonder how much these beams interact with the atmosphere? I can imagine lasers interact little, but wouldn't microwaves heat up water vapor on it's way?
Might be cheaper to build an Tower with PV and battery every 30km than running lines.
Cell-Tower in remote Locations etc.
Lasers have a downside though: optical and near IR light is much more readily absorbed by water vapor than microwaves. I wonder if a maser would be an acceptable solution, if cheaper versions of it existed.
While 1550 nm falls between two absorption maxima of water, so it is not the worst choice, the absorption in water is still more than one hundred times higher than at e.g. 905 nm.
Because of this, 1550 nm is absorbed through fog or clouds at least 3 to 5 times more than shorter wavelengths like 905 nm. Even the latter is absorbed a lot by water, while being much more dangerous for eyes than 1550 nm.
There is no near infrared wavelength where the water absorption is negligible.
See the graphs at:
https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_...
This is an evolutionary step for driving down the cost of high speed backbone capable links perhaps, but it’s not a fiber replacement by any means.
As an engineer, the words "devil" and "details" come to mind.
Satellite radio communications can be monitored, as the signal is cast over a wide area.
Satellite laser communications however, would be much more difficult to tap into.
Uplink went to shit in heavy fog though...
> The Deep Space Optical Communications (DSOC) package aboard NASA’s Psyche mission utilizes photons -- the fundamental particle of visible light -- to transmit more data in a given amount of time. The DSOC goal is to increase spacecraft communications performance and efficiency by 10 to 100 times over conventional means, all without increasing the mission burden in mass, volume, power and/or spectrum.
https://www.nasa.gov/directorates/spacetech/tdm/feature/Deep...
Also, doesn't this have the issue that anything passing through the beam cuts off internet? A bird, a kite, a malicious actor, a dust storm?
The problem of interference from clouds and precipitation is real, but the problem of physical occlusion probably isn't because the satellites move pretty fast. That would make it hard to persistently block the beam unless you have something as big as a storm cloud.
I don't know of any birds or bikes flying around up in space. :D