[HN Gopher] Starlink signals can be reverse-engineered to work l... ___________________________________________________________________ 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! ___________________________________________________________________ (page generated 2022-10-21 23:00 UTC)