[HN Gopher] Starlink signals can be reverse-engineered to work l...
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Starlink signals can be reverse-engineered to work like GPS
Author : SanjayMehta
Score : 257 points
Date : 2022-10-21 12:18 UTC (10 hours ago)
(HTM) web link (www.technologyreview.com)
(TXT) w3m dump (www.technologyreview.com)
| stuckinhell wrote:
| Oh probably shouldn't be sending those the iranian revolution
| then.
| chatterhead wrote:
| Do Starlink sats have the capacity to store IPFS data?
| borissk wrote:
| If one way or another Starlink starts providing precise
| positioning data it will turn their satellites into a valid
| military target in case of a war. E.g. if China invaded Taiwan,
| they may take down the part of the constellation that passes over
| China (if they can cheaply mass produce and launch interceptors).
| aredox wrote:
| They could easily saturate the whole LEO where starlink
| operates with schrapnel - and any damaged sat would add more
| schrapnel, as described by the "Kessler syndrome".
| baq wrote:
| There's nothing easy about what you propose. It requires
| launch capability similar to what SpaceX has, i.e. state of
| the art.
| shadowgovt wrote:
| Given that they have a working space station, I'm certain
| China has enough launch capability to make the Starlink
| orbit hell with several well-placed rockets undergoing very
| dirty disassembly in orbit.
|
| (In fact, among the things that makes that scenario less
| likely is the fact they _have_ a space station and would
| like to keep visiting it without worrying about passing
| through a Kessler cloud).
| panick21_ wrote:
| A space station doesn't mean you have a lot of launch
| capability.
|
| Its and its not clear how you standard rockets can easily
| be used as anti-sat weapons, and if that makes finical
| sense.
| mlindner wrote:
| > Given that they have a working space station, I'm
| certain China has enough launch capability to make the
| Starlink orbit hell with several well-placed rockets
| undergoing very dirty disassembly in orbit.
|
| Yes and their "working space station" is also below that
| orbit. So they'd need to blow up their own station as
| well. Also the international space station as well.
| soperj wrote:
| US had a working space station for over a decade without
| the ability to put people onto that space station.
| shadowgovt wrote:
| This is true, but seems irrelevant because China is self-
| crewing its station.
| ncallaway wrote:
| A Kessler cloud would not persist in orbit at the
| altitude of Starlink satellites for very long.
|
| And building and maintaining a Kessler cloud at that
| altitude seems like it would be... not effective with
| just a handful of rockets due to the significant
| atmospheric drag.
|
| Kessler syndrome is a real concern, but only at higher
| altitudes where atmospheric drag is negligible.
| modeless wrote:
| Kessler syndrome is not "easy" to create at 550km. The orbits
| decay way too fast. Whole satellites decay in 5 years or
| less; smaller debris decays faster due to higher surface area
| to mass ratio. And the orbit doesn't have to decay all the
| way to 0 for the debris to stop being a threat to Starlink; a
| few km is all it would take. I haven't seen a lot of
| calculations about this but my belief is that even
| intentionally creating Kessler syndrome at 550 km would be
| infeasible, and it certainly won't happen by accident.
| godelski wrote:
| That just makes it more likely. If you think war is going
| to last awhile, or you have a severe disadvantage, you shut
| down access to space for a few years. The cost of such an
| attack is lower BECAUSE it resolves itself rather quickly.
|
| Though the issue is that it is substantially harder to
| create the Kessler Syndrome than people claim.
| modeless wrote:
| I disagree that it is at all likely. It would take months
| if not years worth of launches to fill an orbital shell
| with debris and nobody's going to do it before starting a
| war. You don't start a war with the intention of having
| it drag on for years. If you're winning a war you're not
| going to do it and if you're losing a war you're not
| going to have the resources or time to do it nor the
| ability to do the launches without getting your launch
| pads destroyed. Furthermore it doesn't shut down all
| access to space, as you can launch through the cloud to a
| higher orbit.
| tomatotomato37 wrote:
| The point really isn't to completely shut down that orbit,
| just deny it for however long you strategically need.
| Throwing up a huge flak cloud using magnetized cheap metal
| tinsel on an old ICBM isn't only easy, but also has
| actually been done before, albeit for different reasons
|
| https://en.m.wikipedia.org/wiki/Project_West_Ford
| modeless wrote:
| You won't be able to cause Kessler syndrome promptly. It
| takes a while for the collision debris to build up, and
| it takes a while for individual satellites to get hit.
| Space is big and even huge debris clouds will take a long
| time to hit something. It's not going to help your
| invasion next month or anything like that. Very
| impractical as a weapon of war, even if it was feasible
| which it isn't.
| audunw wrote:
| That would be quite dumb. Whatever you put in that orbit will
| decay within a few years.
|
| Given the current situation, USA/SpaceX is in a far better
| position to quickly repopulate LEO with satellites when the
| debris has fallen down. In that case, they may send up
| satellites armed with weapons that can shoot down anything
| being launched into orbit to create debris again.
|
| I don't think entering into that kind of conflict with USA is
| a winning proposition for China unless they have their own
| Falcon 9 or Starship-like rocket.
| vineyardmike wrote:
| > USA/SpaceX is in a far better position to quickly
| repopulate LEO with satellites when the debris has fallen
| down
|
| Until china threatens musks other factories and he
| voluntarily decided that defense isn't a good business for
| SpaceX. Or maybe he'll do what he did with Ukraine and
| advocate for china just to end the war (probably due to
| business risk of Tesla et al).
| sangnoir wrote:
| > Given the current situation, USA/SpaceX is in a far
| better position to quickly repopulate LEO with satellites
| when the debris has fallen down
|
| It's far cheaper to heft tens of thousands of ball bearings
| into orbit vs a single satellite. You can give them a nice
| spread so you have a space shotgun that ruin an orbit for
| years at a time. The decay is a bonus to the attacker[1]
| because they can a go all out during wartime, without
| impacting their long-term space-faring program.
|
| 1. The decay also allows the same armaments to cover a
| larger vertical slice of the orbit.
| basementcat wrote:
| You mean like Project West Ford?
| https://en.m.wikipedia.org/wiki/Project_West_Ford
| sangnoir wrote:
| I was thinking having the projectiles being aerodynamic
| may increase decay time, then realized you can have the
| launch vehicle use solar power to fire the metal spheres
| using a railgun mechanism. This way, you can get vastly
| larger areas of denial by firing at an angle
| perpendicular to that of travel. You can have an every-
| shifting debris field if you fire 2 ball-bearings (port
| and starboard) every 10-50 meters to make that entire
| altitude unusable[1] - not just a specific orbit.
|
| Edit: 1. The perigee and apogee will differ for
| projectiles fired from port or starboard based on launch
| vehicle inclination and the resulting relative speeds to
| earth. It would be a nightmare to track and avoid the
| resulting mess.
| outworlder wrote:
| > In that case, they may send up satellites armed with
| weapons that can shoot down anything being launched into
| orbit to create debris again.
|
| What happened to the outer space treaty?
| modeless wrote:
| Ripped up as soon as you started intentionally trying to
| create Kessler syndrome...
| gojomo wrote:
| In some hypothetical hot conflict where a major
| belligerent nation had already started taking down
| satellites and/or polluting orbits, the treaty will have
| already become a 'dead letter'.
| Rebelgecko wrote:
| As long as they're not using nukes I don't think
| compliance with the OST would be an issue
| modeless wrote:
| Every part of the constellation passes over China. The Starlink
| satellite constellation is practically invulnerable to physical
| attack because it would be prohibitively expensive to hit
| thousands of individual satellites with interceptors. And
| SpaceX can keep launching them, 50 at a time (potentially
| hundreds at a time once Starship is working, along with an
| increase in constellation size to 30,000+).
|
| Physical attacks on the ground stations are more feasible from
| a physics perspective, but now that the satellites have laser
| links you'd have to take out ground stations all over the world
| to completely cut service, not just locally.
|
| The way to attack Starlink would be hacking, either of the
| command and control system or the user terminals. Failing that,
| then jamming, and/or anti-radiation missiles targeted at the
| user terminals. Russia is known to be trying hacking and
| jamming already (recall that they were already successful in
| hacking Viasat at the very beginning of the war). I haven't
| heard about them locating user terminals by their transmissions
| but I'd be shocked if they aren't trying that too.
| [deleted]
| sgc wrote:
| Since 500 terminals a month are being destroyed in Ukraine,
| per Elon, it seems clear they are targeting them.
| mike_d wrote:
| China already has an extensive network of fixed location
| coordinated signal jammers deployed across the country. It is
| regularly used to overpower Radio Free Asia and Voice of
| Tibet broadcasts, and has conducted exercises blocking GPS.
|
| But a much more likely response would be equipping local
| police with direction finding equipment for signals in the
| 10-12 GHz band and bashing in the skulls of anyone found with
| a terminal.
| modeless wrote:
| The military threat of Starlink to China is as a way for
| the Taiwanese defense to communicate during an invasion. In
| peacetime they can prevent Starlink from operating in China
| simply by threatening Elon Musk with the loss of his
| Shanghai factory.
| wolpoli wrote:
| Starlink seems to be protected by the fact that it could
| launch satalites cheaper than the adversary. That advantage
| will hold until the opponent gains the ability to launch
| small satalites at a low cost. Eg. Opponents launches and
| pre-positions mini suicide satalites 100 at a time in orbit,
| leading to a weaponization of space.
|
| Or it might be easier to just pressure Musk's other business
| interests.
| uri4 wrote:
| Not really. To destroy satellite you need suborbital rocket
| with much lower speed. Usually it is a missile launched
| from airplane. Even WW2 V2 missile could propably do it, if
| it had navigation.
| modeless wrote:
| Even so, SpaceX can launch 50 satellites in one launch,
| and each suborbital interceptor can only hit one. And the
| "if it had navigation" part is doing a lot of work in
| that sentence; a satellite interceptor kill vehicle is
| not easy to build. Are 50 of them cheaper than one Falcon
| 9 launch with a 15x reused booster? I think "maybe" is
| the only possible answer, but probably the cost of
| killing all the satellites that way would be around the
| same order of magnitude as putting them up in the first
| place. You would need to build multiple whole factories
| just to make the thousands of interceptors you would
| need.
| Rebelgecko wrote:
| I wonder how hard it is to take out multiple starlink
| satellites right after launch, when they're all on
| essentially the same orbit?
| modeless wrote:
| It's an interesting idea. They are deployed and start
| spreading out within minutes of launch. You might be able
| to take them all out in the first couple of orbits. I
| expect it would be much harder after that. SpaceX could
| possibly defend against this by varying the orbit so you
| don't know where to place your interceptors, and maybe by
| having the satellites boost apart from each other sooner.
|
| But you'd also need to take out most of the on-orbit
| satellites before it would be useful to blow up the
| replacements.
| [deleted]
| mytailorisrich wrote:
| Any communication systems are valid military targets in case of
| war. So much so that they are usually among the first targets.
|
| But there are also other considerations. In your example I
| doubt China would want to provoke the US by shooting American-
| owned satellites out of the sky, and I doubt Starlink would be
| that important anyway.
| VincentEvans wrote:
| Recent actions of Russia in Ukraine have shown how vacuous the
| term "valid military target" is, to the point that there's very
| little sense in discussing it.
|
| (One may argue that along with that it also exposed how
| empirically inadequate are a lot of other terms, institutions,
| conventions, and rules we've become accustomed to relying on
| for maintaining our peace, security, and ensuring that bad guys
| don't go unpunished, but i guess that would be a digression for
| another time).
|
| The meaning behind such terms, absent methods of enforcement
| when they are violated, exists only for those warring states
| that choose to respect them - the list that likely does not
| include any of the realistic opponents we consider today, such
| as Russia, or North Korea, or Iran, or unfortunately, China.
| s1artibartfast wrote:
| Starlink already is a valid military target in time of war.
|
| Also, the way the orbits are established and the fact that
| Taiwan is roughly equatorial, I thin every satellite eventually
| passes over it. Starlink is not geostationary
| chickenpotpie wrote:
| I would be more worried about the undersea fiber optic cable.
| There's 13 cables that provide the vast majority of internet
| into the country and they're deep underwater where they could
| easily be destroyed with no defense.
| njarboe wrote:
| See Nord Stream 1 and 2 for an example.
| dylan604 wrote:
| I'm guessing it's a bit easier to repair/splice a fiber
| break than repairing gas pipes
| rzimmerman wrote:
| There are a few technical reasons I don't see this as a real
| threat:
|
| 1. There isn't a particular part of the constellation that
| passes over China. There are probably a few launch groups that
| never or rarely pass over China, but a majority do. An
| adversary would have to destroy or disable a few thousand
| satellites.
|
| 2. Anti-satellite weapons aren't nearly plentiful enough and
| given the ground support required, I'd be surprised if
| launching more than a few per day is feasible. A counterattack
| would come too quickly.
|
| 3. Precise positions don't help that much. Even knowing a
| satellite position to ~2m still requires some active tracking
| on the interceptor. It's not much benefit over knowing the
| position to 1km.
|
| 4. The debris created would be catastrophic and likely to
| damage the ISS even at Starlink's low altitude.
|
| All of the first three apply to GPS as well even though it's
| only ~32 satellites.
| [deleted]
| dr_orpheus wrote:
| I think there is a bit of an issue here that isn't addressed in
| the article. They reference using the SpaceX published
| ephemerides which are created from the GPS receivers onboard the
| SpaceX satellites:
|
| "SpaceX satellites regularly downlink accurate orbital
| information from onboard GPS. We use this orbital information,
| combined with planned maneuvers, to accurately predict future
| ephemerides, which are uploaded to Space-Track.org three times
| per day" [0]
|
| So using the positioning information of the SpaceX satellites is
| already dependent on GPS. Saying that it could be used as a
| backup to GPS is a bit non-sensical to me. Sure you could go back
| to using ranging measurements for each of the satellites to get
| TLEs from NORAD or LeoLabs or one of the other commercial space
| tracking companies, but it would likely be less accurate and not
| updated as frequently as the SpaceX satellites don't have a
| precision clock onboard for timing and propagation like the GPS
| satellites do.
|
| [0] https://www.spacex.com/updates/index.html
| jenny91 wrote:
| They're different failure modes. It's unlikely the GPS
| constellation will go dark anytime soon. It's much more likely
| you're in an area without good view of the (few) GPS satellites
| required for a fix; or that there is GPS jamming, etc.
| dr_orpheus wrote:
| Ah, that is true I didn't consider it from that perspective.
| It may also serve as a decent anti-spoofing measure if you
| compare the two results for position that you are getting
| directly from GPS vs from the Starlink satellites.
| [deleted]
| helsinkiandrew wrote:
| Presumably GPS can be jammed locally on the ground and confuse
| ground terminals but not at the range required to block the
| SpaceX satellites reception in low earth orbit.
| brandmeyer wrote:
| At least one party in the conflict is generating enough
| interference on the ground to obstruct both GPS and GLONASS
| navigation in orbits passing over the region. Its loud enough
| to _detect_ as soon as the region is visible (thousands of
| miles away).
|
| Hawkeye360 detected GPS interference and geolocated it to
| Russian forces shortly before the invasion, but at this point
| it could easily be both parties.
| shafoshaf wrote:
| Aren't the Russian drones using GPS? Why wouldn't Ukraine jam
| GPS?
| sangnoir wrote:
| I'd assume the Russian drones would default to GLONASS
| soperj wrote:
| why wouldn't that be just as easy to jam?
| cozzyd wrote:
| It's basically the same frequencies too
| bombcar wrote:
| It's harder to jam GPS for "just one side" so doing so
| would harm both side's operations.
| cozzyd wrote:
| Although I wouldn't be surprised if one side is more
| likely to have dual-band GNSS receivers...
| dr-detroit wrote:
| thfuran wrote:
| Couldn't the US re-enable Selective Availability?
| dismalpedigree wrote:
| Theoretically yes, but with massive disruption in the
| civilian space.
| dmurray wrote:
| DGPS [0] is a workaround for SA. If you can have a ground
| station with a known location somewhere in the same area
| - even 100 miles away should be OK - you can broadcast
| the correction.
|
| DGPS was already "good enough" in 2000 when SA was turned
| off, so I'd expect it could achieve very close to the
| same precision as regular GPS by now.
|
| [0] https://en.m.wikipedia.org/wiki/Differential_GPS
| [deleted]
| mike_d wrote:
| The random Chinese consumer drones, sure. You could also
| just block wifi to knock out most of them too.
|
| Current block military drones being imported from Iran are
| not vulnerable to GPS manipulation because they have backup
| inertial navigation systems.
|
| After Iran steered an American drone using false GPS
| signals, the US also implemented inertial and celestial
| navigation systems. https://en.wikipedia.org/wiki/Iran%E2%8
| 0%93U.S._RQ-170_incid...
| jandrewrogers wrote:
| This is false. All US military navigation systems,
| including the referenced drone, are primarily inertial
| and always have been. These systems can optionally accept
| fine-tuning GPS corrections, but only if those
| corrections are within the tight (classified) error
| margins of the inertial navigation system. It is a
| misconception that the US has ever used GPS for primary
| guidance in weapon systems; even cheap throwaway weapons
| like JDAM are primarily inertial. The kind of influence
| possible via manipulation of GPS is measured in meters.
| State-of-the-art INS technology is now good enough that
| the US military is considering phasing out GPS
| corrections for some newer systems.
|
| GPS was designed for the purpose of accurately measuring
| the Earth during peacetime to build a precise model the
| world that could be used for inertial navigation systems
| in wartime. It was never intended to be used as a
| critical navigation system since it could be trivially
| destroyed by the Soviet Union when it was designed.
| Civilian systems tend to not concern themselves with this
| vulnerability and therefore happily use it for
| navigation.
| nverno wrote:
| In that article, they claim that the American drone was
| already using inertial navigation.
|
| > American aeronautical engineers dispute this, pointing
| out that as is the case with the MQ-1 Predator, the MQ-9
| Reaper, and the Tomahawk, "GPS is not the primary
| navigation sensor for the RQ-170... The vehicle gets its
| flight path orders from an inertial navigation system".
| mlindner wrote:
| Your last line seems wrong. American aircraft have had
| inertial navigation since forever. GPS is a more recent
| addition. GPS is easily jammed and that's always been
| known to be the case. Nothing would be solely dependent
| on GPS.
| ortusdux wrote:
| Are the phased array antennas utilized by the starlink
| satellites and user terminals more resilient to jamming?
| jvanderbot wrote:
| GPS jamming occurs local to the receiver, not the
| transmitter. So, you'd have to worry about the dish on your
| roof / vehicle, not the ones on the satellite.
|
| I'm that sense, a phased array can help by filtering out
| signals that are not in line of sight with your satellite,
| but only one satellite fix does not provide a great
| estimate of the receivers position. Esp when signal
| strength is used to estimate bearing.
| fragmede wrote:
| well, anyone having to deal with you (and I) do. I
| wouldn't put it past a APT to be able to do better and
| take action in space if their hand were forced.
| gameshot911 wrote:
| Interesting! Is it theoretically possible to launch a
| "GPS jamming" satellite constellation? And if so, could
| you do it with far less satellites than the quantity you
| are attempting to jam?
| idealmedtech wrote:
| Phased array antennas are mostly for getting programmable
| beam forming, and don't have much to do with jamming, which
| works by destructively interfering with incoming waves.
| Starlink operating on a different frequency means that GPS
| jammers won't be able to jam them out of the box, but
| presumably if they're jammers built in the last 20-30 years
| they'd have onboard SDRs which can dynamically hop
| frequencies. It's a neat trick to get GPS from Starlink,
| but won't stop nation state attackers from jamming access
| to GPS.
| wl wrote:
| Jamming isn't destructive interference, which would
| require knowledge of the exact signal being sent as well
| as the exact location of the transmitter and receiver.
| Jamming is overwhelming the receiver with a stronger
| signal in the same frequency band so the weaker one
| cannot be received. Think someone screaming over someone
| else whispering.
|
| Phased array beamforming absolutely helps with jamming.
| Jamming is all about reducing the signal to noise ratio
| in the channel until it is unusable. Directional antennas
| (of which phased arrays are electronically steerable
| versions) have more gain in the direction of the desired
| signal and less towards unwanted signals located in
| another direction.
| [deleted]
| colechristensen wrote:
| The gps antennas on the starlink satellites will be pointed
| "up" i.e. away from the earth's surface. Jamming from the
| ground to a receiver in space pointed away from earth would
| be... difficult. Especially when the satellites orbit about
| every 90 minutes, so you'd really have to do a global very
| very loud gps attack... it'd be simpler trying to hit
| several gps satellites with missiles than to accomplish
| that.
| adgjlsfhk1 wrote:
| no, but they're a different frequency so if someone was
| only jamming GPS, this would get through.
| Tuna-Fish wrote:
| They are massively more resistant to jamming. The
| antennas are very good at rejecting signals that are
| coming from the wrong direction, that is, not from above.
| brandmeyer wrote:
| It depends strongly on how the phased array is being
| steered. If the components prior to phasing and summation
| are saturated by the interference then phased array
| beamforming will not reject the interference.
| mike_d wrote:
| Phased arrays are good at rejecting incidental
| interference, which is why they were used to address
| radar jamming. Of course that also meant that billions
| were poured into developing technology to counter that
| resilient property. Anyone capable of blocking GPS on a
| non-trivial scale would be easily capable of blocking
| Starlink as well.
| WJW wrote:
| This is the correct answer, phased array antennas have
| much more directivity so they are much harder to jam with
| a ground-based jammer. Although I suppose in some cases
| you might want to put the jammer on a drone anyway, to
| cover a larger area. In that scenario you would probably
| not see a significant difference for phased array
| antennas vs "normal" antennas.
|
| Caveat btw: for both starlink and GPS, the satellite you
| are talking to will not always be "up". For GPS in
| particular, it is possible that some of the satellites
| are only barely above the horizon. So an antenna that
| only looks "up" is generally not what you want anyway,
| which makes ground-based jammer more effective again.
| gjsman-1000 wrote:
| Well... if it is that easy, might as well make the sequences
| proprietary again (change them for security), but it should not
| cost very much after all to add such functionality. At least not
| nearly as much as Elon thought.
| belval wrote:
| I think the article makes it clear that SpaceX does not care
| much about security here. It's more that they don't have
| (engineering) bandwidth to actually put something together and
| sell/support it.
|
| Focus is a very real thing in business, starting an additional
| product that has a minimal overhead can still end up ~2-3 years
| later as a massive cash drain with a complex hierarchy of
| workers with a very small ARR. That's why you take on customers
| before building it.
| iwillbenice wrote:
| The one note I will mention about SpaceX and caring about
| HW/terminal security is the subsidized cost. SpaceX is
| retailing the terminal I bought for $500, while I understand
| the hardware all-in is north of $2000.
|
| In these scenarios you will usually see the vendor default to
| locking down the platform/hardware, if for nothing else to
| prevent people from buying it and re-purposing it due to
| subsidized components included.
| Animats wrote:
| This is straightforward to do if you have some reference ground
| stations listening to the satellites. That's how WAAS works. If
| you have ground reference stations receiving and broadcasting
| offsets, you can derive navigation info from any set of long-
| range RF sources which have some pattern to which you can sync.
|
| The U.S. Army has "pseudolites" which do this for short
| distances.[1] These are used as a backup to counter GPS jamming.
|
| [1]
| https://www.army.mil/article/169033/Pseudolites_preserve_pos...
| t0mas88 wrote:
| You can even do this with simple AM radio stations. Tune an
| aircraft's ADF to the radio station frequency, get a bearing to
| the transmitter and then do the same with another station. From
| both bearings you can figure out where you are as long as you
| know where the transmitters are.
|
| It's conceptually similar to what they did here with the
| Starlink signal but using very different technology.
| kazinator wrote:
| > _Crucially, this could be done without any help from SpaceX at
| all._
|
| "We can get this information without Microsoft's help at all. In
| our callback, we just add 60 to the address of the NMHDR
| structure we have been passed on the stack, and dereference that
| as a DWORD to peek at an undocumented variable in the caller
| whose existence we reverse-engineered ..."
|
| https://news.ycombinator.com/item?id=33270518
|
| These people come across as naive. To have a long-term working
| solution that can have an industry around it, they are going to
| have to commit to a program of continuously monitoring the
| Space-X signals for changes and roll out corrections, and
| possibly do more reverse engineering. Those corrections would
| have to be rolled out to every navigation device which depends on
| this.
|
| That's why Musk said no; he doesn't want to commit to that sort
| of thing, where he can't make a change in the configuration of
| satellites or their signals due to that breaking the dependent
| navigation system.
|
| Would you even want to give one company that much power? You've
| got no contract with Musk saying that he has to provide satellite
| signals. Now suppose you make millions of navigation system
| deployments dependent on it. On a whim, Musk can enact changes
| that will break all those systems, wreaking havoc. He could use
| that power as a negotiating lever. E.g. if he is taken to task by
| some regultory body over something, he can give them a "friendly
| reminder" that he controls an important, widely used navigation
| system without any obligation to keep it working.
| rongopo wrote:
| That's how GPS works, it was initially intended for something
| else --- was it for detecting nuclear blasts?
| MichaelCollins wrote:
| Not for detecting nuclear blasts, but rather for directing
| them. The primary motivation for Transit/NNSS, the first
| satellite navigation system, was to provide location
| information to missile submarines so they could calculate
| firing solutions for SLBMs. The submarine needs to know where
| it is so it can tell the missile where to go.
|
| Detecting nuclear blasts from space came shortly later with
| Project Vela. Those satellites didn't depend on something like
| GPS because the position of each satellite at any given time
| could be calculated from its known orbital parameters; no need
| for radio navigation.
| outworlder wrote:
| > The submarine needs to know where it is so it can tell the
| missile where to go.
|
| That reminds me of "the missile knows where it is because it
| knows where it isn't"
|
| https://www.youtube.com/watch?v=bZe5J8SVCYQ
| hotpotamus wrote:
| I thought the idea for GPS went back pretty much to Sputnik.
| People realized pretty quickly they could track it by timing
| its signals from a known location on Earth and then also
| quickly realized you could reverse that and figure out where on
| Earth you are once you have enough timing signals from known
| locations in space. It just took a bit for the computers to get
| small enough and for us to put up the satellites.
| dingaling wrote:
| That's correct and led directly to the US Navy's doppler-
| based Transit GNSS that operated from 1961 until 1996.
|
| Navstar / GPS emerged as a joint project in 1973 based on
| individual services' research into a better form of GNSS.
| mmaunder wrote:
| GPS is also coupled with WAAS which relies on a network of ground
| stations at known coordinates to determine GPS error. These
| errors are caused by bulges in the ionosphere that throw off
| timing. Error is calculated, broadcast up to satellites and then
| rebroadcast down to GPS receivers that are WAAS enabled. This is
| known as a satellite based augmentation system. The other
| satellite nav systems that compete with GPS are building similar
| augmentation systems (like GAGAN, EGNOS, MSAS and SDCM). These
| systems are required for precision approaches like LPV for
| aircraft on instrument flight plans. Regular GPS precision due to
| ionosphere changes is too low. They've enabled the FAA to lower
| the minimums for GPS approaches down to levels that are close to
| ILS, removing the need for expensive ILS installations at many
| regional airports. So replacing GPS isn't just about creating a
| system to locate a point in space. You'd need to replace critical
| systems like WAAS that enable precision approaches during
| instrument conditions, for example.
| arsome wrote:
| I mean I think both directions here make sense: SpaceX doesn't
| want to invest engineering effort on this when they're not even
| profitable and there's no profitability to be seen from
| navigation, while researchers can do a little reverse engineering
| and make something workable without the need for that engineering
| investment.
| ensignavenger wrote:
| If the DoD really wanted it bad enough, it could be very
| profitable. I take the situation to mean that while there may
| have been some interest from the DoD, it wasn't enough to make
| it worth SpaceX's time.
| moralestapia wrote:
| I don't think the DoD and GPS are enough revenue to offset
| the massive CapEx of building Starlink. Their ROI lies in
| providing internet to the whole world, so its's reasonable
| they're not allocating time/money on this.
| dmix wrote:
| And being laser-focused on a particular market/model is a
| critical part of any early business succeeding.
| axg11 wrote:
| There's no profitability from navigation? Starlink could charge
| a massive premium for high resolution GPS.
| arsome wrote:
| But GPS is already so widely deployed and you can't really
| compete with free.
| ceejayoz wrote:
| If someone starts taking out the 24 GPS satellites - a new
| anti-satellite weapon, or an interceptor satellite like the
| X-37 is speculated to be - being able to do it off
| Starlink's thousands as a backup would be _extremely_
| appealing to the US government.
|
| (After all, this is the same organization that's happy to
| pay out the nose to keep ULA alive to have redundant launch
| options.)
| manquer wrote:
| GPS satellites don't sit in LEO . All ASAT weapons
| demonstrated so far by any country has been only for LEO
| based satellites.
| ceejayoz wrote:
| That would be why I said "new", yes.
|
| Given that we can get satellites to GEO, we can
| presumably get one that goes boom up there, should we be
| so inclined.
| dahfizz wrote:
| The US military would come down on them pretty hard.
|
| We already have premium high resolution GPS. Its for military
| use only.
| mschuster91 wrote:
| > We already have premium high resolution GPS. Its for
| military use only.
|
| So what, throw down an RTK pod and now you have like
| centimeter level accuracy. That's stuff anyone can buy for
| COTS drones, I'm eyeing on it for my DJI drones.
|
| The only thing needing realtime in-flight accuracy of that
| level _without_ an RTK pod is weaponry and _maybe_ cars
| outside of road (because on road, they can augment GPS with
| camera data and road mappings).
| snovv_crash wrote:
| Even without RTK, the new dual-band receivers have 30cm
| accuracy. That's enough for any nefarious activity I can
| think of.
| pcl wrote:
| I don't think that's true any more. IIRC, the high
| resolution codes were disclosed to the public in the late
| 90s / early 00s, and there have been no efforts to rotate
| them since.
|
| Extra precision can be achieved with fixed-point
| augmentation signals, which I believe is common at airports
| and construction sites. I would assume the at militaries
| similarly augment signals in theaters of war. But that's
| different than some separate high-resolution mode.
|
| At this point, so many civilian services depend on the
| high-resolution data that I'd be pretty surprised to see
| GPS going back to a two-tier system.
|
| A citation for the above:
|
| "In May 2000, at the direction of President Bill Clinton,
| the U.S. government ended its use of Selective Availability
| in order to make GPS more responsive to civil and
| commercial users worldwide.
|
| "The United States has no intent to ever use Selective
| Availability again."
|
| https://www.gps.gov/systems/gps/performance/accuracy/
| RegnisGnaw wrote:
| There is already a 2 tier system. Clinton turned off
| "Selective Availability" but kept the P(Y) code for
| military only use. The P(Y) code now has been
| supplemented by an M code for military on the newer
| generation of GPS.
| dhsysusbsjsi wrote:
| The way GPS was designed to work originally is two sets
| of codes. Course Acquisition (CA) code which repeats at
| 300ms intervals with a deliberate bias was designed to
| bootstrap the receiver into locating its position in a
| 1-week Precise (P) long code. This bias was selectively
| worse in different regions and I think still can be
| changed in war zones. Happy to be educated further here!
|
| What the US government did was remove the bias from the
| CA code so it could be used for precise positioning. The
| military still uses P codes as well. I believe there is a
| small gain to be had but it's due to frequencies.
|
| Since then there have been several more advances, mostly
| to broadcast local augmentation signals. Wide Area (WAAS)
| and Ground Bases (GBAS) are common in receivers.
|
| L5 is a new band to help solve multipath error in urban
| areas.
|
| Most receivers also have remote autonomous integrity
| monitoring, where it can predict its own area of
| probability (by using groupings of 4 in 5 satellites),
| and if it's too large for the intended use case, alert
| the user. Also with 6 satellites it can calculate
| combinations of 5 satellite groupings to work out (and
| exclude) faulty satellites. This is Fault Detection &
| Exclusion (FDE).
|
| Mobile devices will also download their own separate high
| resolution almanac and ionospheric data over the internet
| which is superior to the low data rate GPS almanac. It
| can also use known cell locations to approximate its
| position. Combined, this enables rapid (hot) signal lock
| immediately onto the correct satellite code & Doppler
| shift frequency, which is why your mobile gets a fix in 3
| seconds, versus your car which takes minutes.
| lxgr wrote:
| Selective Availability being phased out and is no longer
| a feature on the most recent GPS satellites:
|
| https://en.wikipedia.org/wiki/Error_analysis_for_the_Glob
| al_...
| Qqqwxs wrote:
| > What the US government did was remove the bias from the
| CA code so it could be used for precise positioning. The
| military still uses P codes as well. I believe there is a
| small gain to be had but it's due to frequencies.
|
| The precision of positioning from the P code is 10 times
| greater than the C/A code (about 30cm vs 3m). This is due
| to the wavelength/'chip length' of the code signal which
| is modulated onto the carrier wave (10.23 Mhz / 29.31 m
| wavelength for P code, 1.023 Mhz / 293.1 m wavelength for
| C/A code). Positioning precision is limited to about ~1%
| of the chip length by signal processing.
| WJW wrote:
| This is correct, but I'd like to add that at some point
| the errors from which frequency and code you use is no
| longer the dominant factor in the position error.
| Depending on where you are, either multipath errors (eg
| due to reflections from buildings or mountains) or
| athmospheric errors (ie due to the radio signal being
| distorted in the ionosphere) start to dominate.
| MichaelCollins wrote:
| > _The US military would come down on them pretty hard._
|
| Or maybe they'd just buy an exclusive contract.
| stevehawk wrote:
| high resolution gps already exists. lookup WAAS
| jrockway wrote:
| WAAS is nice but dual-band receivers provide similar
| accuracy levels without needing to see that satellite.
| Ublox quotes on their ZED-F9P datasheet 1.5m accuracy for
| GPS+GLONASS+Galileo+BeiDou, increasing to 1m accuracy if
| using space-based augmentation (WAAS, EGNOSS, MSAS, GAGAN).
| Even without a SBAS, if you can do RTK, you can get 0.01m
| accuracy. (The corrections from a nearby reference station
| are even better than what you can get from a satellite.)
|
| RTK is probably more available than people think. My state
| offers a public network of continuously-operating reference
| stations; you can sign up for a free account and then do
| whatever RTK madness you desire. https://cors.dot.ny.gov/
| if you happen to be in New York.
|
| (I realize now that I really wanted to reply to the person
| complaining about not being in North America, but oh well,
| maybe they'll find this.)
| mindslight wrote:
| But the state-run reference stations are generally too
| far away from you to get that sweet sweet 1cm accuracy...
|
| It's amazing what you can do with consumer-priced gear
| these days. I set up a Sparkfun ZED-F9P breakout board as
| a fixed beacon on my roof, and then their "RTK Facet" as
| the rover to do precise measurements to create a map. I
| could have done the basic thing I needed to by hiring a
| surveyor or eyeballing things with a tape measure, but
| this is much more general.
|
| The GNSS software world seems to be a mess though, ripe
| for a paradigm shift. For example, QGIS seems to be based
| on flat projections with transformations rather than
| 3d-native - from what I can tell, QGIS seems to consider
| the "degree" to be a unit of length measurement! This
| leads to ridiculous things like being able to
| accidentally measure a nonsensical "cartesian" distance
| between two points that differs from the actual distance
| by a factor dependent on latitude.
|
| I've still got to tidy up my own pipeline that lets me do
| things like turn N (point, distance) samples into a
| single point. I would have thought that type of operation
| would be common, but thinking about how surveyors work I
| guess they're usually locating points optically, rather
| than trying to position a GPS receiver at the point to be
| measured.
| jrockway wrote:
| Yeah the software is ... interesting. I'm actually less
| than a mile away from a reference station, but don't get
| 1cm accuracy because I don't have a much of a sky view
| from my apartment's window. (But I'm moving soon and have
| a great sky view. And am closer to the reference
| station!)
|
| Another thing you might find interesting is that you can
| generate a report on how good your reference station is.
| It's actually in Sparkfun's documentation, so you're
| probably aware, but if not:
| https://learn.sparkfun.com/tutorials/how-to-build-a-diy-
| gnss... Specifically the part where you collect data with
| u-center and upload the results to https://webapp.csrs-
| scrs.nrcan-rncan.gc.ca/geod/tools-outils... for analysis
| was very interesting.
| AlotOfReading wrote:
| GIS software is indeed messy, but not because the people
| writing it don't know what they're doing. You seem to be
| approaching things from a Cartesian perspective, but GIS
| almost always works in spherical coordinates because the
| earth is (approximately) a sphere. It makes a lot of
| common operations easier too.
|
| Imagine you go on a road trip (along the surface of the
| earth). How far have you driven? In spherical
| coordinates, that's just changing two angles. In
| Cartesian coordinates, it's an ugly mess. Doesn't hurt
| that it's a lot easier to measure angles in surveying
| than distance.
|
| However, certain GIS systems like QGIS and arcGIS are
| designed for making maps and have to display things in a
| 2D space. Thus, they have a projection mapping the
| spherical coordinates to Cartesian canvas coordinates and
| back again. This leads to unintuitive behavior, but it's
| mathematically hard to do better.
|
| Now, the user interfaces and the terminology and the
| subtly disastrous inconsistencies between different data
| sources? Hot flaming garbage, all of it. These aren't
| problems with the underlying data models though.
| NKosmatos wrote:
| https://en.wikipedia.org/wiki/Wide_Area_Augmentation_System
|
| "Currently, WAAS satellite coverage is only available in
| North America"
| oritsnile wrote:
| There is also the European version of this EGNOS, besides
| there also private Providers like TerraStar
| KaiserPro wrote:
| > Starlink could charge a massive premium for high resolution
| GPS.
|
| but then they'd have to make it reliable. We are also not
| sure how much more (if at all) accurate it is.
|
| sure the bandwidth of the downlink is much higher, and louder
| than GPS, but the accuracy of the clocks on the satellites is
| much less. More importantly they are not characterised, so we
| arn't sure how much they drift due to temperature (both from
| sun and other effects.)
|
| depending on the navigation type, visual positioning might be
| better/faster/more accurate. For "military" purposes, silent
| autonomous navigation without radio sensors is pretty
| appealing. Using satellite imagery, its perfectly possible to
| make an accurate, robust visual navigation system
|
| for urban areas, "VPS"s are far quicker and more accurate,
| but require network access to work practically.
| natch wrote:
| TV satellite signals have been used like this for decades. I sat
| through a company pitch on this and one of the advantages was it
| (TV, not Starlink) penetrates buildings and for example
| underground parking lots way better than GPS signals.
| madars wrote:
| Massively impressive! A very exciting paper
| https://arxiv.org/abs/2009.12334v4 from the first two authors
| shows how Starlink can be fused with ordinary GNSS to get
| extremely impressive +56 dB anti-jam advantage (see Figure 1).
| loceng wrote:
| Elon on Twitter was saying it can be made much more accurate
| than GPS, just that it's not a priority for them.
| CamperBob2 wrote:
| My guess is that the reason they terminated work with the UT
| Austin researchers is that they've signed a commercial deal
| with someone else that hasn't been announced yet.
|
| GPS-independent PNT (position/navigation/timing) is a
| significant area of both market and military/civil government
| interest right now, and has been for a while. They won't be
| indifferent to it at SpaceX or at any other organization that
| operates or plans a constellation.
| shadowgovt wrote:
| It's a neat trick, but I wouldn't rely on it for the same reason
| I recommend against relying undocumented behavior in an API: if
| Starlink isn't intended to be a global positioning system, then
| they can change anything in the protocol at any time to improve
| its utility for its intended purposes as the expense of its
| utility for GPS.
|
| That's annoying if your RPC library is now broken because you
| assumed order of unrelated events wouldn't change. In a GPS it
| can direct you off a cliff.
| RajT88 wrote:
| This is good advice, for sure, and I've received it from wise
| colleagues in the past.
|
| Where I land on this is: Undocumented behavior can be useful if
| you're doing something which is short in duration, and narrow
| in purpose. Don't build a product off it, though.
|
| I guess in this case, it could be useful for a fallback
| positioning mode for the military or something.
| yazzku wrote:
| "OFDM is all the rage," says Mark Psiaki, a GPS expert and
| aerospace professor at Virginia Tech.
|
| Did a Virginia Tech professor really say "it's all the rage"?
| ck2 wrote:
| More and more devices already have GPS L5 chips which is accurate
| to a foot
|
| The problem is altitude. I can't get my watch or phone to give me
| proper altitude anywhere. Within a meter would be amazing forget
| a foot.
|
| https://barbeau.medium.com/tl-dr-dual-frequency-gnss-on-andr...
|
| https://barbeau.medium.com/crowdsourcing-gnss-capabilities-o...
|
| https://docs.google.com/spreadsheets/d/1jXtRCoEnnFNWj6_oFlVW...
| t0mas88 wrote:
| Try a WAAS or more general an SBAS receiver, they give accurate
| altitude information. Accurate enough to land an aircraft with.
| ortusdux wrote:
| I've been wondering how precise Starlink could get with
| positioning if they put some effort into it. Maybe add some
| dedicated hardware to the much larger 2.0 batch of satellites. If
| they felt they could surpass what is available via GPS, I could
| see them integrating Starlink uplinks into Teslas to aid their
| self-driving efforts. Adding always on data would be a bonus.
| kloch wrote:
| More precision would require an atomic (hydrogen or cesium)
| clock on each satellite, and periodic adjustments for
| relativistic effects, just like regular GPS and other GNSS
| systems.
|
| An intermediate improvement might be a small/lightweight
| rubidium clock synced to GPS to improve stability for when GPS
| is unavailable to the satellite.
| oliwary wrote:
| Yes! This could be so exciting. Given that starlink satellites
| are much more numerous and much closer than GPS satellites, I
| wonder what the lower bounds are for possible accuracy. Imagine
| a globally available positioning system with 1cm accuracy and
| 30 updates per second... (compared to 1 time per second for
| GPS) This could be a revolution for VR, robotics, logistics and
| so many other fields.
| aredox wrote:
| And for cruise missiles.
|
| (Maybe you should read why GPS is not more accurate: it's not
| a technical limitation, it's done on purpose.
|
| Also try to read up on Chesterton's Fence.)
| snovv_crash wrote:
| This changed over 20 years ago, GPS no longer has
| artificial limitations for accuracy.
|
| You can't get commercial GPS receivers licenced unless you
| restrict the altitude and speed they operate at, but a
| dedicated self-built receiver technically doesn't need to
| have these restrictions. There are SDR+software projects
| that do this, which could technically be used for ICBM
| guidance with no restrictions.
| mattanimation wrote:
| I had an inkling that Todd's team would be behind this. They do
| awesome work!
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