[HN Gopher] SpaceX sends laser-linked Starlinks to the polar orbit
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SpaceX sends laser-linked Starlinks to the polar orbit
Author : CarCooler
Score : 121 points
Date : 2021-01-25 18:07 UTC (4 hours ago)
(HTM) web link (www.teslaoracle.com)
(TXT) w3m dump (www.teslaoracle.com)
| jcims wrote:
| I wonder if they will eventually offer network access from orbit.
| Ship a turnkey module with a 10G ethernet port out the
| back...that'd have to be worth a couple million dollars a year.
| wmf wrote:
| Every time a Falcon 9 gets loss of signal I wonder if only
| there were satellites they could uplink to instead of using
| ground stations.
| jccooper wrote:
| NASA runs satellites for this purpose, TDRS, in GEO. But
| they're for NASA use only, so SpaceX only gets them on Dragon
| flights (and maybe other NASA payloads.)
| jsmith45 wrote:
| Regulations allow some commerical use of this system:
|
| > For a fee, commercial users can also have access to TDRSS
| for tracking and data acquisition purposes.
|
| This comes from a rulemaking that updated the regulation.
| See: https://www.federalregister.gov/documents/2012/02/10/2
| 012-26...
|
| See the actual active regulation at 14 CFR 1215.
| asadlionpk wrote:
| flat earthers won't like that /s
| jccooper wrote:
| Starlink's too low to offer reasonable coverage for orbital
| stations. Even payloads lower than the constellation (and there
| aren't many) would only see very small beams, and would pass
| through them quickly. And the laser system, I think you'd
| basically have to be co-orbital with them to work.
|
| That would be a better product for the traditional GEO comsat
| operators, but apparently there's not enough market there for
| them to bother. NASA already has a system for that, TDRS. I
| wonder how busy it is nowadays?
| [deleted]
| NikolaeVarius wrote:
| How long before we get space-70-1 cloud region with
| Cloudflare/Cloudfront serving cached data from orbit?
| _Microft wrote:
| Computing produces a lot of waste heat which is difficult to
| deal with in space. The cooling system of the ISS can radiate a
| total of 100kW for example.
|
| I think it is unlikely that we will see data centers in space
| unless it is absolutely unavoidable, e.g. because of lag
| between Earth and the place (in space) where the data is
| needed.
| hinkley wrote:
| Starlink's target is lower latency (because speed of light in
| low earth orbit is 30% higher than speed of light in fiber
| optics).
|
| A CDN sending or storing their consumer facing data via
| satellite makes no sense. But control plane data? Maybe.
|
| Cut 30 ms off of SF to NYC and how you manage consensus might
| change quite a bit.
| fastball wrote:
| I had this same thought back in December!
|
| https://twitter.com/acnebs/status/1336078364046667777
| benlivengood wrote:
| Caches are to trade off latency and bandwidth for cost. It's
| cheaper to put normal servers in regional colos to serve a lot
| of local customers, probably not cheaper to put expensive
| servers in orbit to serve a varying and small set of customers
| below a satellite.
|
| I can see running HSMs in space; probably the most cost-
| effective physical security available.
| Dylan16807 wrote:
| Even if satellites were free to launch and had unlimited
| bandwidth, that would be slower than installing servers where
| the ground stations plug in. So, uh, how much are people
| willing to pay for novelty?
| mikepurvis wrote:
| There may be some ground stations owned by WISPs or whatever
| servicing a whole community, but I think the theory is that a
| lot will be small end user terminals providing connectivity
| to just a household or two in a remote location. If these are
| your users, then yeah, it could very well be advantageous to
| have and orbital CDN if millions of them are all streaming
| the same new Cobra Kai episode at the same time or whatever.
| jandrese wrote:
| I was thinking it would be more attractive to people who
| want to host content that is problematic inside of national
| borders. Basically treat space like international waters so
| you can host your Pirate Bay or 8Chan or whatever outside
| of national jurisdictions.
| mikepurvis wrote:
| If Starlink was knowingly hosting dubious/illegal content
| in space, wouldn't the media companies simply make the
| case that each individual jurisdiction revoke their
| license to the radio spectrum?
| jandrese wrote:
| That would be a tough case to make I think. Spectrum
| allocations are hard to change. I can't think of any case
| where they were threatened as part of a legal dispute.
| teeray wrote:
| > Musk has confirmed on Twitter that the black pipe-type objects
| at the end of each Starlink satellite are actually laser links.
|
| Translation for all beltalowda: "Bossmang say each satellite have
| a tightbeam"
| walrus01 wrote:
| BELTALOWDA!!!
|
| https://www.youtube.com/watch?v=cnpQCIDePh8
| cbm-vic-20 wrote:
| This is a great show if you enjoy physics.
|
| Way OT, but the patois/creole used by the Belters is well
| done, too.
|
| This actress (Cara Gee) in "real life":
| https://youtu.be/f20fkrf1d5A?t=101
| nitpick_dingo wrote:
| I don't agree that it is a great show if you enjoy physics.
| In fact, I'd say the show does a headfake towards physics
| which leads people to think it is reasonable.
|
| It is "good physics" the same way _The Martian_ is good
| physics. Neither is actually close....but they're far
| better than you see in Battlestar Galactica.
| jrrrr wrote:
| Is it at least the least-bad show if you enjoy physics?
|
| Do you know of other fiction that does it better?
| generalizations wrote:
| And then again, Battlestar Galactica is far better than
| what you see in Star Wars.
| matmatmatmat wrote:
| I'm gonna have to disagree here. Sometime back in season
| 2 or 3 they had a shot where a rocket engine's flame cone
| passed through a girder and it lit up due to the change
| in temperature. I mean, that's borderline nerd
| pornography.
| walrus01 wrote:
| It's all relative, I mean we're using a benchmark of all
| previous television scifi having "magical antigravity
| technology where every ship has standard gravity pulling
| everything to the interior decks"... It's not a really
| high benchmark to meet to have at least a LITTLE BIT of
| plausible science, like spaceships oriented like flying
| office blocks with internal ladders/elevators, and thrust
| gravity.
| Symmetry wrote:
| I recently read the book Eccentric Orbits about the Iridium comms
| system that was a lot like this (recommended by the way). One of
| the technical issues that was mentioned in it was that the
| satellites had to correct for the Doppler shift in the
| frequencies they used to talk to each other because of the high
| relative speed they were traveling at. I wonder if these
| satellites have a similar problem or if lasers are so directional
| they can afford to not be too discriminate in what frequencies
| they accept.
| thatcherc wrote:
| Generally optical comms systems in space are not affected by
| Doppler shift because of their modulation scheme, not the
| directionality of the beams. They tend to use some type on-off
| keying (sometimes called OOK) where data is encoded in the
| pattern or duration of fully on and fully off laser pulses. If
| there's a variation in the frequency of laser light being
| received, it'll still just register an on or off signal on the
| photodetector on the receiving spacecraft. Radios, on the other
| hand, use modulations that rely much more on the actual
| frequencies and phases of the radio signals they receive,
| making frequency shift due to Doppler a much bigger factor.
|
| The radio encoding schemes are more efficient in a bits per Hz-
| of-EM-spectrum sense, but optical systems have the advantage of
| being at such a high frequencies that even "inefficient" coding
| schemes can reach very useful datarates.
| lgats wrote:
| Forward and back looking lasers would have minimal speed
| difference, side laser links don't appear to be at extreme
| speed differences according to these hypothesized connections:
| https://youtu.be/QEIUdMiColU?t=132
| snoshy wrote:
| Since the linked article is somewhat ambiguous about this, and
| other commenters appear to be getting confused about the purpose
| and value of the laser links as well: these laser links are
| purely intended for satellite-to-satellite communications for
| Starlink. They are not (at least at this time, and for the
| foreseeable future) intended for ground-to-satellite
| communications.
|
| The value that sat-to-sat laser links provide is that they create
| a low latency, high bandwidth path that stays within the Starlink
| satellite network. Before these 10 satellites, each Starlink
| satellite has only been capable of communicating directly to
| ground terminals (either consumer, transit, or SpaceX control).
| For traffic that is intended to move large geographic distances
| (think transcontinental), this can require several hops back and
| forth between ground and space, or the traffic from the user
| terminal is exited at a node that is geared for transiting
| traffic and most of the data transits along existing ground
| Internet links.
|
| By performing this type of transit directly in space, and exiting
| at a transit node nearest the destination for the data, you
| greatly reduce latency. Bandwidth still might not be great, but
| what this does is unlocks a very financially lucrative consumer
| use case: low latency finance traffic and critical
| communications. There are many use cases around the world where
| shaving even 10-20 milliseconds of latency on a data path can
| unlock finance and emergency capabilities, and this is a long
| fought battle throughout the history of these industries. As an
| example, if you got a piece of news about a company in Australia,
| and wanted to trade on it as quickly as possible in USA, if you
| can beat your competitors by 10-20 milliseconds, that can mean a
| lot of money.
|
| Laser comms for Starlink sats have long been planned, but have
| historically proven to be quite hard to get working. They also
| depend on a sufficient critical mass of satellites so that a
| given sat actually does have another sat within lock to send the
| traffic towards.
| iso1631 wrote:
| Not just low latency. Without satelite-satelite communication,
| both grounds stations have to be able to see the same
| satellite.
|
| In GEO that's not a problem - a lot of the planet is in sight.
| You have a ground station in New York and you can bounce off a
| satellite over the Atlantic and land the signal in Nigeria just
| fine.
|
| With Starlink the orbits are really low, so the distance to the
| ground station is low. That's fine if you are in the backwoods
| in Washington and bounce to a receiving station 100 miles away
| in Seattle, it's no good if you're at sea, or (in this case) at
| an Antarctic station -- one which can't even see GEO satelites.
| Gravityloss wrote:
| The field of view from the satellite is 5000 km, though
| reception probably gets a lot worse at lower angles for a
| multitude of reasons. Hope I calculated right.
|
| https://www.wolframalpha.com/input/?i=2*6300*arccos%286300%2.
| ..
| walrus01 wrote:
| the starlink beta test customer terminals only have a cone
| shaped view of suitable beam forming ability and gain above
| them, so the 4000 km is a lot less in usable practice. they
| can't talk to a satellite that's 15-20 degrees above the
| horizon for instance, it'll only work when the satellite
| rises higher in its general field of view.
| walrus01 wrote:
| big chunks of antarctica where _most_ of the research base
| population is located can see geostationary, just at a very
| low look angle. the whole peninsula, mcmurdo and places at
| similar latitudes to mcmurdo.
|
| it's the pole that has problems seeing geostationary, and has
| up until very recently been totally dependent on 7-8 hours of
| coverage a day using big tracking antennas to talk to old
| geostationary satellites that have wandered somewhat out of
| their original orbits, so that from the POV of the earth
| station at pole, they can be communicated with part of the
| time.
| snoshy wrote:
| Yea I'm guessing a bunch of researchers at both poles must
| be rejoicing at the potential for new connectivity this
| creates with the polar launch.
| walrus01 wrote:
| The US DoD and Soviets, Russians somewhat solved this
| problem by putting molniya/tundra orbit communications
| satellites into orbit for narrowband data and voice, text
| comms. Has been a thing for 35+ years.
|
| But there has been nowhere near enough money available to
| do something like set up a pair of molniya orbit
| satellites with long apogee dwell times over the center
| of antarctica.
| Diederich wrote:
| > Bandwidth still might not be great
|
| Right, compared to reasonable in-ground ISPs.
|
| I think Starlink sat to Starlink sat links will also help
| bandwidth, specifically in the case where a given downlink
| connection is heavily utilized, the system can shunt traffic to
| another slightly less ideal but less utilized ground station.
|
| > unlocks a very financially lucrative consumer use case
|
| That's a bingo! I think there's a pretty good chance that this
| could turn into a pretty epic cash cow for Starlink.
| chasd00 wrote:
| i'll certainly be a customer when it comes online. I'm
| building a cabin where no connectivity is currently
| available. (well aside from spotty 3g cell)
| rtkwe wrote:
| I do wonder how much of a draw Starlink will be versus
| terrestrial microwave for things like HFT firms. Guess it
| will do really well for linking further afield exchances like
| Hong Kong and NYSE where a straight line microwave route
| isn't practical so the extra distance added by the orbit
| doesn't matter as much.
| walrus01 wrote:
| a lot of serious HFT for transcontinental stuff moved to HF
| radio some years back, with big-ass yagi-uda antennas aimed
| between locations like the CME datacenter, london, tokyo,
| new york.
|
| it's very low data rate but also guaranteed lower latency
| than the submarine cables.
| rtkwe wrote:
| OK so even that will be hard to break into except as a
| wider bandwidth option which would have some applications
| the HFT, but it'd be hard since latency is king there.
|
| Maybe with that out of the picture other uses like
| telepresence for remote surgery can edge in. I've been
| waiting for a while for that to really take off seems
| like an awesome way to provide services you couldn't
| afford to to remote places.
| Diederich wrote:
| > latency is king there
|
| I have read that Starlink, given sat to sat relays,
| should be able to beat any possible ground based system
| as long as the distances are great enough. Does that
| match your understanding of this?
| walrus01 wrote:
| a lot of theory and conjecture about sat-to-sat laser
| relays has been published by people (and youtube videos
| made, etc), but many of these theoretical topologies are
| dependent on plane-to-plane communications which will be
| difficult to aim and maintain links on.
|
| if you google 'starlink train' and look at some videos,
| when a batch of 60 starlink satellites is launched
| ,they're all at the same orbital inclination. they remain
| at the same inclination but as the weeks go past after
| their launch, they are spread out to follow each other at
| several hundred km spacings. but they're still following
| each other in what is basically a strung out conga line
| of satellites. communications between forward/rear
| satellites in the same batch should not be nearly as
| difficult to aim.
|
| what would be difficult to aim and maintain links on
| would be cross-plane links between two different sets of
| satellites, with very high differing relative velocities.
| rtkwe wrote:
| My understanding is it's tough to beat point to point
| microwave arrays for directness in a lot of cases,
| they're already pretty close to the straightline path
| between some locations. The same is basically true for
| the longer range low bandwidth links that curve around
| the Earth.
|
| Starlink is at a disadvantage because fundamentally it's
| pathing across a sphere with a larger radius so even when
| the path is direct across the Starlink cluster it still
| has to traverse a longer distance than the equivalent
| path on the ground. Adding to that the path won't always
| be directly across the surface of the constellation,
| depending on where you are and where the destination is
| you'll find some pockets where the link has to zig zag
| across the constellation slightly adding to the
| additional link distance. This [0] isn't necessarily a
| perfect representation but it does show how starlink's
| linking may work and how it's not a perfect net. It also
| doesn't account for the acquisition times for new laser
| links which were on the order of 20 seconds in another
| laser sat link test.
|
| [0] https://youtu.be/AdKNCBrkZQ4?t=103 (it's also
| comparing fiber to Starlink where the best in class now
| is radio links generally)
| nickik wrote:
| The real value is not super low latency communication, but
| rather airplanes and ships out of reach of normal base
| stations.
|
| I have seen no evidence that traders will be the primary users.
| Do you have any evidence or cases where they are doing or
| planning this. Are you just guessing?
| temp667 wrote:
| In my space especially with video conferencing people are
| willing to spend a premium for lower latency for audio /
| video conferencing links. So there may be a market there (if
| you can backhaul phone, video, audio conference traffic)
| where even 10 - 20 ms in savings may be noticable.
|
| Another may be gaming.
|
| Another is as you say planes and ships out of reach of ground
| stations (very sparse situation however).
| xibalba wrote:
| So are these laser equipped says inserted between/within the
| "chain" of previously deployed starlink says?
| NortySpock wrote:
| Either they will retire old chains of satellites or just
| start new chains.
| ceejayoz wrote:
| The older satellites self-retire after a couple years,
| anyways, just by running out of fuel and deorbiting.
| snoshy wrote:
| Not quite. In order for a laser sat to talk to another sat,
| the second sat needs to also have laser comms hardware on it.
| Given that these were the first 10 to boast of such hardware,
| initially they'll only be talking to each other. Over time,
| as Starlink pitches more sats into orbit with laser comms,
| they will have more and more peers to talk to.
|
| As the sister comment implies though, Starlink sats are in
| low Low-Earth-Orbit (LEO) so they experience non-zero drag
| from the atmosphere. This slows them down, causing them to
| gradually fall back to Earth, creating a natural expected
| service lifetime for each satellite in orbit.
|
| So the expectation is that SpaceX will have to continually
| put up more and more replacements indefinitely as older sats
| decay and burn up in the atmosphere. These 10 laser sats are
| just the latest among a string of sats that are yet to come
| online with newer and better capabilities.
| employedbydlr wrote:
| German aerospace agency DLR sent a laser terminal for satellite
| to ground communication on the same ride-share ->
| https://www.dlr.de/kn/desktopdefault.aspx/tabid-17435/
| JumpCrisscross wrote:
| Sat-to-sat laser links are also much more secure than undersea
| cables.
| ornornor wrote:
| Can't anyone (well, anyone with state kind of money) observe
| the laser and at least dump it with perfect accuracy to keep
| for later decryption? I'd think tapping n undersea cable is
| more work than observing light going from sat to sat? I'm
| just spitballing here, I have no idea what's possible or not
| but I'd be curious to know.
| jandrese wrote:
| I think it would require someone to fly a spy sat up near
| one of the SpaceX sats. From the ground the atmosphere
| would attenuate the signal too badly and you'd only have
| visibility for a few minutes at a time as it passes
| overhead maybe.
|
| In practical terms I don't think it's a major concern. Much
| more likely that the spy agencies would tap the lines
| coming out of the ground stations.
| JumpCrisscross wrote:
| > _Much more likely that the spy agencies would tap the
| lines coming out of the ground stations_
|
| Which is a significant step backwards for _e.g._ Russia.
|
| Currently, all data between Asia and North America runs
| on cables. Anybody can spy on those. If those data did
| satellite laser hops, only those with ground stations
| would have access. Everyone else gets locked out.
| sfblah wrote:
| The company I work for changed its internal routing of
| data to use encryption for 100% of traffic crossing the
| public internet. I have to think everyone else is doing
| this as well. Is spying on cables like this even useful?
| How would ay usable data be extracted?
| jandrese wrote:
| You can learn a lot from the metadata and packet
| size/timing.
| JumpCrisscross wrote:
| > _Can't anyone (well, anyone with state kind of money)
| observe the laser_
|
| LEO is far from a true vacuum. But it's sparse enough that
| you have limited beam scattering. Getting a read on a sat-
| to-sat laser emission from the ground is nontrivial.
| bob33212 wrote:
| If it is encrypted and you drop just a couple bits due to
| noise you can't read it.
| TeMPOraL wrote:
| What about scatter from the satellite itself? The laser
| can't be perfectly absorbed on the receiving end. I
| haven't done the calculations, but I fully expect the
| spot size is much larger than the receiver.
|
| That said, I imagine that for any serious bandwidth, you
| won't get enough SNR to decode anything from the ground.
| anonymousiam wrote:
| Military inter-satellite links deliberately choose laser
| wavelengths that do not propagate well through Earth's
| atmosphere. Such links could only be intercepted from a
| space-borne platform. I have no idea what laser wavelength
| StarLink is using, so it may not apply here.
|
| I have no doubt that (like every other geo-mobile satellite
| constellation) the system allows for "port mirroring" on
| point-to-point links, or (more likely) relays everything
| through a ground station even when doing so has performance
| implications. This allows them to fulfill their obligation
| to government(s) surveillance.
| walrus01 wrote:
| if your potential adversary is a five eyes nation state
| intelligence agency with the ability to sniff traffic from
| 10/100/200GbE submarine fiber DWDM links, the fact that
| spacex/starlink is also a US company and subject to national
| security letters and other monitoring won't help you.
| bilbo0s wrote:
| Likely wouldn't help even if it wasn't Five Eyes.
|
| At some point, the communication has to enter the
| terrestrial network. That entry node is likely to be under
| the influence, if not outright control, of Five Eyes
| security infrastructure.
|
| You would need to build out a lot of infrastructure to
| escape the sort of ubiquitous surveillance that is
| available to those organizations.
| benlivengood wrote:
| There are lots of fascinating problems to solve.
|
| The telemetry and tracking itself for the laser links. All the
| satellites need fairly accurate orbital information from all
| other satellites; there will be several thousand satellites
| capable of performing autonomous orbital adjustments to avoid
| debris and for their own station keeping. There has to be a
| convenient and reliable fallback for automatically syncing
| satellites with the rest of the network after a reboot or loss
| of communication.
|
| The packet network needs to maintain an efficient routing table
| and provide low packet loss to end-users. My guess is that the
| only practical choice will be establishing a large number of
| point-to-point channels with their own retry/error-correction
| management. TCP/IP isn't capable of dealing with more than
| about 1% packet loss and I doubt raw optical/wireless links
| will be reliable enough especially with topology changes,
| requiring extensive store-and-forward hardware to buffer
| transmissions waiting for a reliable route or de-duplicating
| multicast packets at the receiving end. Reassembly and de-
| duplication on receipt is theoretically feasible; if a tight
| reception window can be maintained then specialized hardware
| could filter duplicates sent over 2 or 3 redundant routes to a
| local receiver without increasing observed latency or using
| unreasonable amounts of RAM. A combination approach could allow
| a tradeoff between using double or triple the raw bandwidth but
| providing low-latency reliability vs. higher latency with
| retries while maximizing throughput depending on the current
| network load. It could also be hardcoded for different traffic
| classes.
|
| I'm not involved in this problem space in any technical
| capacity but it sounds like a very fun set of problems to
| solve.
| snoshy wrote:
| SpaceX continues to genuinely feel like a practical
| intellectual's playground. They really do have so many
| fascinating problems to work on.
|
| Accurate orbital information might not be necessary or
| possible, if you can perform broad scanning that can quickly
| lock in your given target, but it certainly doesn't hurt. The
| issue is that even having an orbital track, because of the
| sats being so low in LEO, atmospheric drag will change your
| orbit rapidly enough that this information can get out of
| date quite fast.
|
| Convenient and reliable fallbacks I feel are largely a solved
| problem for SpaceX. They've built their Starlink bus by
| reusing a lot of the software from the Falcon 9, Dragon, and
| Starship programs that already had to handle even greater
| levels of reliability.
|
| Routing and retransmits are indeed quite a novel area for
| this kind of service. But the laser link will only be locked
| on one other peer satellite at any given time, and I don't
| think they plan on reorienting the sats in order to establish
| laser comms because of the effect it would have on drag as
| well as albedo. The former impacts service life per sat, and
| the latter has been a big rallying cry for Starlink
| opposition due to the impact it has on astronomy and the
| visible sky.
|
| So if you likely can't reorient to retransmit, your only
| options are the peer laser link or the ground transit exit
| node, either or both of which might not exist, but I feel
| like you would just ack the packets on each hop to your peer
| and leave it at that.
| martinald wrote:
| I think the other important use case is that sats without a
| ground station in view can backhaul traffic to another set of
| sats (for cruise ships or remote islands).
| walrus01 wrote:
| even just the ability to hop 1 satellite can greatly extend
| the range of one spacex earth station. right now, as the
| parent poster mentions, the moving LEO satellites need to be
| simultaneously in view of the CPE antenna and a spacex earth
| station.
|
| and also relatively overhead of the CPE antenna, since the
| starlink customer terminal is a phased array that does dual
| beamforming in a 'cone' of view directly above it. just
| because a satellite is visible 5, 10 or 15 degrees above the
| horizon from the POV of the CPE doesn't mean it can talk to
| it. the system is definitely reliant upon a fairly high
| satellite density.
|
| with the ability of the satellite that's generally overhead
| of a starlink earth station to talk to the satellites
| immediately behind, and preceding it in its orbital plane,
| and then those two additional satellites to talk to the CPEs
| underneath them, the possible coverage area can be greatly
| increased.
|
| 3D visualization of starlink orbits and coverage footprints:
|
| https://satellitemap.space/
| briffle wrote:
| I had a friend that worked at the south pole for a year. They
| had a few hours a day they could access their main
| communications satellite. Something like this could be a game
| change for remote research stations..
| ChuckMcM wrote:
| Exactly, there was a great animation posted here once that
| showed the hobs with and without lasers. Given that there are
| examples of 44+ terabits[1] being transmitted optically I am
| not too worried about the bandwidth.
|
| I'd love to be on the Starlink team, they are building some
| really cutting edge stuff. There are not many places or times
| where you can have such a big impact on the world and their
| team happens to be one of them. Good times.
|
| [1]
| https://www.sciencedaily.com/releases/2020/05/200522095504.h...
| snoshy wrote:
| This seems overly ambitious, and not likely to translate to
| laser satellite comms links. Remember these sats are in low
| LEO, so there is at least some amount of non-uniform
| atmospheric medium to create optical distortion that you
| wouldn't have in a tightly controlled environment from your
| link (chip, datacenter, what have you).
|
| Then there's the issue of signal attenuation at distances
| like these, along with the power budget from the solar panels
| to ensure that you aren't burning all your power just on
| laser comms.
|
| I can't imagine these links would be anything more than 1:1
| at any given time, at least not at first. Maybe later they
| might be able to handle simultaneous laser links from 1:3 or
| something like it, but I highly doubt that's their current
| capability.
|
| Even some of the best latest ground-to-sat laser comms links
| are on the order of ~7 gigabits per second. [1] I imagine
| those are far larger sats than Starlink, and their entire
| power and thermal budget is likely spent on comms. And the
| ground stations can be orders of magnitude larger and power
| hungry in relation to a Starlink sat. Note also that this is
| from GEO, so you aren't likely having to handle substantial
| relative movement either.
|
| [1] https://en.wikipedia.org/wiki/Laser_communication_in_spac
| e#2...
| jacquesm wrote:
| So, why not apply? You certainly have the required skillset
| and with your experience level I'd assume they would jump at
| the opportunity.
| hprotagonist wrote:
| phase change maneuvers are expensive.
| innot wrote:
| Does that mean that polar regions now also get coverage? Great
| news for my Chukotka dacha!
| zaroth wrote:
| There are two different explanations that I've read over the last
| few months for why we didn't see laser links on previous rounds
| of Starlink satelites.
|
| First, that the unit pricing was too high. SpaceX is targeting an
| extremely (absurdly) low price of $250,000 BOM per satelite, and
| it was theorized that the laser links were blowing the budget.
| Estimated that it would cost ~$100k for the lasers, targeting,
| and electrical systems to add the links.
|
| Second, I've read that they had issues guaranteeing that all the
| components of the laser system would fully burn up in the
| atmosphere. One of the conditions of launching low-orbit
| satellites is that they will fully burn up on re-entry (therefore
| not posing any risk when they fall back down to earth).
| Apparently some of the optics components had a chance of survival
| and ultimately possible land-impact.
|
| I'm not sure if we can say that this launch indicates that the
| cost issue has been solved. It could be worth blowing out the BOM
| to get some operational experience having a few birds with the
| lasers, so perhaps they haven't fully solved the pricing issue
| unless we start seeing lasers on every subsequent launch.
|
| TFA has a great animation of a polar orbit. It's basically a
| longitudinal orbit, so it will absolutely pass over land for a
| lot of the time, so clearly they must have at least solved the
| burn-up issue, if in fact that actually was ever an issue in the
| first place.
|
| Also, FYI, there was a scheduled attempt to launch SN9 today, but
| it just got scrubbed a minute ago due to winds. They will be
| trying again tomorrow! reddit.com/r/spacex is a good place to
| watch for updates:
| https://www.reddit.com/r/spacex/comments/krllbt/starship_sn9...
| neaanopri wrote:
| It's probably the BOM cost.
|
| I've seen the "burn up in the atmosphere" constraint before,
| and it struck me as a bit crazy for Shoot First and Ask
| Questions Later SpaceX to care about this
| jccooper wrote:
| Demisability is a significant regulatory concern... but I
| suspect it wasn't flying before mostly because they didn't
| have it working yet.
| temp667 wrote:
| They are explicitly pursuing a demisable sat design.
|
| Note - despite other posters claims, this is not a
| requirement and there are other approaches as well for the
| safety side here. The most common is to deorbit into the
| ocean (the sats are maneuverable) with a failure rate and
| part hazard rate low enough that remaining risk is minimized.
| I would expect they would deorbit into ocean / near non-
| populated areas for other reasons as well.
| jandrese wrote:
| That requirement could have come from the government. It's
| not a crazy thing to ask for when you're launching literally
| hundreds of satellites into LEO.
|
| Plus, the last thing SpaceX wants is a news story about
| killer satellites raining debris on innocent citizens.
| Remember that each satellite launched has to be deorbited
| eventually, so if they're launching dozens of sats per month
| they'll eventually be deorbiting dozens of sats per month. If
| they don't fully burn up each one will have a chance of
| hitting someone. Sure the chance may be very small, but when
| you're rolling the dice dozens or hundreds of times per month
| eventually you're going to land on snake eyes.
| Robotbeat wrote:
| There are multiple reasons, from demisablility to BOM cost and
| also just that the tech wasn't quite ready at first and they
| wanted to launch ASAP to get that minimum viable product up and
| running (besides their FCC licenses have a time limit for
| deployment... if they don't deploy their network fast enough,
| they can lose access to the spectrum they want to use). They
| also wanted to be able to bid for broadband subsidies, etc.
|
| Lots of good reasons they just launched before the laser links
| were ready. Also, they don't necessarily need them except for
| really, REALLY remote customers (ie a minority), so they can
| sprinkle in lasers into their constellation as they become
| available.
| giantg2 wrote:
| I'm confused by the word "the" in "the polar orbit". Shouldn't it
| just "polar orbit" without the "the"?
| kdmytro wrote:
| Why?
| gundmc wrote:
| Yes, the title implies there is a single polar orbit when polar
| orbit could be one of many orbits with particular
| characteristics (passes over/near the poles). It's awkwardly
| worded
| coolspot wrote:
| For others like me who are wondering how much bandwidth could be
| realistically achieved between sattelites, here is one real-world
| product from the company "Tesat":
|
| > The laser terminals supplied by Tesat needed less than 25
| seconds on average to lock onto each other and begin transmission
| in both directions at 5.6 Gbit/s.
|
| https://www.laserfocusworld.com/lasers-sources/article/14104...
|
| Napkin math: that's 56 clients using constant 100 MBit/sec. With
| overbooking coefficient of 0.01, that's 5,600 clients on 100
| MBit/sec plan per sattelite with 1 MBit/sec guranteed.
| modeless wrote:
| To be clear, that refers to a demo system unrelated to
| Starlink. I don't think it is known where the Starlink lasers
| come from or what their capabilities are.
|
| All I know about them is that a reason they weren't deployed in
| the first batches of satellites is their original design
| included parts that did not burn up completely on reentry, and
| SpaceX wants Starlink satellites to always burn up completely,
| since there are thousands of them.
| Robotbeat wrote:
| Another company that is doing 10Gbit/s. Considering a single
| Starlink satellite will have 4 laser links plus has a total
| radio bandwidth of about 20Gbit/s, this is sufficient.
| https://www.reddit.com/r/Starlink/comments/en7dtx/comment/fd...
|
| ...however, this is nowhere near any fundamental limit on
| optical transmission. SpaceX is operating around 20-40GHz
| radios, and let's just say a bandwidth 1% of the frequency with
| a SNR of 1, giving them a bit rate per channel of
| 200-400Megabits/s. The same calculation with near IR optical
| (which is optimistic obviously) gives 3 Petahertz frequency,
| 30THz bandwidth, and 30terabits/s/channel. So optical is
| nowhere near any kind of fundamental limit, unlike radio which
| needs many channels (ie phased array, MIMO, spatial
| multiplexing generally, etc) to saturate the bandwidth of the
| satellite bus.
|
| (Also, note that broadband users have a capacity factor of like
| 1-2%, so on average 20Gbps can give service to like 10,000
| subscribers per viewable satellite using 100Mbps peak service.)
| bpodgursky wrote:
| SpaceX is disgustingly undervalued at $92 billion.
|
| I would pay a 4x multiple to be able to dump my own money in
| here... sadly, I am not a billionaire, and have no access to this
| market.
| deeviant wrote:
| I agree with your assessment.
|
| Alphabet owns a reasonable chuck of spaceX, which is the
| easiest to way to gain exposure.
| itsoktocry wrote:
| > _SpaceX is disgustingly undervalued at $92 billion._
|
| Maybe, maybe not. None of these things have proven to have a
| profitable business model, so how are deriving the value?
|
| Of course, if that doesn't matter to you, there are myriad ways
| to hand your money over to SpaceX.
| bpodgursky wrote:
| Uber's market cap is $100B and it's not a proven profitable
| business model either.
|
| SpaceX has wildly bigger upside if the big bets pay off.
| matmatmatmat wrote:
| I mean, maybe Uber's way overvalued?
| chronic3802 wrote:
| You can purchase pre-IPO shares in SpaceX (minimum investment
| $250K) if you have $1M in net worth.
| bpodgursky wrote:
| Where? I didn't think any of the pre-IPO marketplaces took
| investment at that level.
| lgats wrote:
| Some platforms offer to purchase employees options and then
| resell them on a secondary marketplace
|
| https://equityzen.com/company/spacex/
|
| Minimum investment I've seen is $20k, but I personally
| haven't seen SpaceX available
| Metacelsus wrote:
| How?
| hinkley wrote:
| > In the U.S., the term accredited investor is used by the
| Securities and Exchange Commission (SEC) under Regulation D
| to refer to investors who are financially sophisticated and
| have a reduced need for the protection provided by
| regulatory disclosure filings.
|
| In a pre-IPO company, VCs and other investment groups
| consider unaccredited investors to be a liability, and
| they'll either give worse terms or no terms. If you're
| worth a million bucks the SEC considers you to be a grown-
| up and that you'll ask questions rather than being spoon-
| fed data that can help you protect your investment, which
| takes away a bunch of scenarios where you can litigate.
|
| I worked at a company that turned out to have an
| unaccredited investor. I didn't hear the details but they
| had to 'fix it' before the VCs would move forward with
| discussions. (They still didn't get the money.)
|
| GP's implication is that if you have a million bucks you
| can get (are?) accredited, which will give you access to
| private shares. I've heard this too, but I couldn't tell
| you the details.
| bpodgursky wrote:
| I am an accredited investor and make (small) investments
| on a number of platforms (ex FundersClub, AngelList), but
| have never seen healthy late-stage pre-IPO companies like
| SpaceX on any of them.
| hinkley wrote:
| My read was that they were alluding to sites that allow
| employees to sell their options/shares to non-employees.
|
| FundersClub and AngelList are more executive-focussed
| sites, aren't they?
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