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SR-71's “R2-D2” Could Be the Key to Winning Fights in GPS Denied Environments
- s4vi0r 8y agoLuv too celebrate imperialism, very cool
- arama471 8y agoWhat?
- deleted 8y ago[deleted]
- dproblem 8y agoSummary: You an mix the coordinates obtained from celestial navigation (stars) with signals of opportunity (Electromagnetic sources like FM) to find the position without GPS. Problems: Anytime a military advertisement happens (LN-120G Stellar-Inertial-GPS from Northup G.) - if you don't see the total price of the unit, know that it was a waste of money and resources.
- brownbat 8y agoPeople often focus on the potential of quantum computing, but generally focus far too little on the potential of quantum sensing. We revolutionized the precision of timekeeping with atomic clocks. Quantum inertial sensors could precisely track your location with very little drift and no satellite constellation maintenance. https://www.newscientist.com/article/mg22229694-000-quantum-positioning-system-steps-in-when-gps-fails/ https://www.newscientist.com/article/mg22229694-000-quantum-...
- DoctorOetker 8y agosych a device would still require synchronization, it promises lower drift, but to eliminate drift you will always need to recallibrate to synchronize with reference points (stars, beacons, GPS, ...)
- sgt101 8y agoI wonder what kind of improvement you can get by using several of the devices at once? Could some sort of consensus monitoring at least tell you what kind of margin of error you are working with ? I guess for some applications being 100m out is fine (for example an Astute in open ocean), but getting it that wrong in, for example, the Med or the Sound of Skye is probably a problem.
- planteen 8y agoStandard error decreases by the square root of the number of samples. So an order of magnitude improvement would need 100 sensors!
- mattkrause 8y agoThat’s true when averaging together iid samples, but you could probably do something smarter if you know about the likely errors and the sensors’ covariance. For example, if three of the four sensors agree, you should probably completely disregard the fourth, rather than averaging it in.
- robotresearcher 8y ago> you could probably do something smarter Assuming measurements are independent and errors are Gaussian, the Kalman filter is this smarter thing. Variants exist for nonlinear systems. https://en.wikipedia.org/wiki/Kalman_filter https://en.wikipedia.org/wiki/Kalman_filter
- justinjlynn 8y agoOf course, when you decrease the size of the sensor by half in each dimension while maintaining its error rate you've quadrupled the number of sensors. If you can increase the computing power similarly, or decrease the computing requirements for combining those sensor measurements - it quickly becomes feasible to use massive numbers of sensors to improve the standard error significantly - but it is a lot of ifs. Practical example, you'd only have to shrink the sensor by half 6 or 7 times to fit 100 in the same area as 1.
- sgt101 8y agoReally interesting : I was aware of the 2018 announcement reported in the FT but I have never seen this 2014 article before.
- pithon 8y agoEven quantum sensors will need something (i.e., another sensor) to stabilize the vertical channel. The effect of imperfectly compensating the gravity component out of the specific force measurements from the accelerometers leads to a positive feedback loop. Finite precision arithmetic and fundamental algorithm error (solving the Bortz equation) leads to errors that will grow in the horizontal direction as well.
- tomohawk 8y agoBefore the days of GPS in the cockpit, a relative of mine was a 747 captain doing routes across the Pacific. On one flight, all of the gyros went offline. He had been trained in the US Air Force in celestial navigation, so he was able to use that to get the aircraft within range of a beacon, and land safely.
- gcb0 8y agowouldn't a simple compass have sufficed if they weren't off route?
- dproblem 8y agoInverting compass readings into position is highly problematic because of interference, and noise.
- gonzo41 8y agoThere'd probably be too much metal / electrical interference for a regular compass to work.
- gruez 8y agoPlanes don’t have built in compasses? edit: yes they do https://en.wikipedia.org/wiki/Flight_instruments https://en.wikipedia.org/wiki/Flight_instruments
- danaliv 8y agoAirplane compasses are indeed affected by the electrical system, but not so much as to make them unusable. A maintenance process known colloquially as "swinging the compass" involves turning on the electronics, positioning the aircraft over a compass rose painted on the ground, and noting the error at various bearings. As for the metal, most metal airframes are aluminum.
- hermitdev 8y agoA compass would probably be of marginal utility if you're flying a "great circle" route across an ocean. For instance, if you were to fly non-stop from Chicago to London, your initial route will have you heading north east, but at the end, you'll be heading south east.
- DoctorOetker 8y agodoes anyone know if astro navigation systems deduce time from star transits (or rather generalized star transits, so they don't need to actually be momentarily collinear, i.e. a database of stars with their distances included)?
- dproblem 8y agoYes, they do. The only time it works is when you have a clear view, which is not always.
- planteen 8y agoThe article mentions a "highly accurate chronometer" in regards to the Blackbird. So I don't think they deduce time from the stars. Rhubidium atomic clocks are quite compact and not all that expensive. Hobbyist electronics people buy retired ones from cell phone base stations for an accurate 10 MHz sync signal in their home labs. https://www.eevblog.com/2012/01/14/eevblog-235-rubidium-frequency-standard/comment-page-4/ https://www.eevblog.com/2012/01/14/eevblog-235-rubidium-freq...
- joshvm 8y agoThe SR-71 carried a clock accurate to a hundredth of a second [1]. It used that, combined with current observed locations of the brightest stars in the field of view to determine location (with reference to a catalogue). More info here: https://books.google.co.uk/books?id=6svmtOFa1JIC&pg=PA65&lpg=PA65&dq=sr-71+chronometer+accuracy&source=bl&ots=pwGcwkO8ZI&sig=ACfU3U3YySJdhfKYta20kOoI6LyXU72nrw&hl=en&sa=X&ved=2ahUKEwjt-u6mpqrhAhUTsHEKHXKcCFkQ6AEwCnoECBsQAQ#v=onepage&q=sr-71%20chronometer%20accuracy&f=false https://books.google.co.uk/books?id=6svmtOFa1JIC&pg=PA65&lpg... What do you mean by a transit in this case?
- DoctorOetker 8y agoit is possible to deduce location of the earth on its orbit around the sun, and hence the time by star transits: https://en.wikipedia.org/wiki/Transit_instrument https://en.wikipedia.org/wiki/Transit_instrument consider for example 2 very distant stars, and a closer star in the middle, and all of them in a plane perpendicular to the ecliptic. as the earth rotates, the closest star seems to move left/right with respect to the "vertical" defined by the more distant stars. from such a star transit you know the earth has just passed through the plane defined by these stars, and hence know the earth's position, hence the time. in the past catalogues for transits were optimized for human use, i.e. close to each other, ... but a modernized i.e. software solution should not need such proximity, and could make use of all the visible stars to make a more accurate assessment. I was kind of asking if there were any free open source software, it would be kind of neat to have an emergency laptop (with some optics) loaded with openstreetmap and astronomical positioning software, ...
- dingaling 8y agoI don't see why they have to reach back and summon the mystic name of the Habu when astronav is still flying on the B-2 and Trident SLBM. It's not as if we have fogotten that the technology exists, it's just that GPS is non-mechanical and more deployable, cheaper and robust. Side project I've wanted to do for years: smartphone AR app that you point at the night sky and it does the star recognition and calculations automatically. But I've no illusions that it would be much less practical than just using the onboard GNSS receiver.
- hermitdev 8y agoIt's about redundancy and failure modes. The fine article mentions this. What if GPS is jammed or spoofed? What do you do then? Celestial navigation gives a fallback (albeit with less accuracy). Regarding your side project - Google Sky does the opposite already. Point your phone at the sky, and it tells you what stars, planets, constellations, etc are there.
- sansnomme 8y agoThe issue is light. Your typical smartphone camera in its default package simply cannot get enough light to create a stars-against-dark-background image regardless of how much machine learning and signal processing you throw at it. It's much easier when you have a massive roof mounted lens. There are ways to improve gain and boost the optical signal but there are limits to what's possible in a smartphone without hardware additions or modifications (even with dual cameras like modern flagships).
- joshvm 8y agoYou could probably do it with a Pixel (or something else with night sight) and astrometry.net.
- sansnomme 8y agoDoesn't work, unless you have a tripod and use a significant exposure time. Perhaps. It's nowhere near "AR" levels. If you are going to go that far, save yourself some trouble and get a proper astrophotography setup. Also, astronomy.net is overkill for this.
- inetsee 8y ago<rant> This is one of the most obnoxious websites I have ever encountered. It popped up an ad covering the content. I clicked on the close ad "x" like I always do. Then another box popped up asking if I never wanted to see this ad again, and I replied "yes". Then another box popped up asking why I didn't want to see this ad. I replied, and another box popped up saying the ad had been closed by Google. That box remained over the content for 3 or 4 seconds. That box eventually faded, but literally 2 seconds later, another ad popped up, covering the content, and I clicked the back button. I will never click on a story from that website again. </rant>
- foobarian 8y agoI clicked the back button, and nothing happened. I looked at the history, and sure enough the site had inserted a few of its own URLs. :)
- inetsee 8y agoThis is another pain point for me. I learned quite some time back to right-click on the back button to pull down the history, then click on the url I want to go back to.
- inetsee 8y ago<unrant> I must confess that when I went to the website containing this article, I was using a second computer that I rarely use, which did not have an adblocker installed. My primary computer has Firefox Privacy Badger installed, and when I went back to the article, using my adblocked machine, the experience was much less obnoxious.</unrant> What I HIGHLY recommend now is that if you don't have an adblocker installed, do so. Privacy Badger, UBlock Origin, etc, whatever you prefer. I still see ads, but the experience is infinitely less obnoxious.
- exabrial 8y agoWhenever someone asks me to explain how GPS works, I give the example given in the article: Sailors used to track the position of stars in the sky. Since stars are hard to see during the day, and you can see them through walls, we put some artificial stars in the sky that we can identify easy and we put enough of them there's always a few above you.
- rocqua 8y agoNot the best of analogies. With stars, you measure angle above the horizon and compass heading of the star. With GPS you are measuring time-delay of a signal. Those are two very different ways of navigating.
- paulsutter 8y agoGPS signals aren't cryptographically signed. It's a bizarre oversight since it could prevent spoofing. I guess it's just another example of the tradition for zero-security software. If nothing else, the current interest in cryptocurrency will train a new generation of developers to trust no message.
- swixmix 8y agoThis exists for the military -> https://en.m.wikipedia.org/wiki/Selective_availability_anti-spoofing_module https://en.m.wikipedia.org/wiki/Selective_availability_anti-... Also, there are other methods to find position data.
- paulsutter 8y agois there any reason not to sign all gps signals?
- coldacid 8y agoHow often would keys be rotated, and can that be done from the ground? And then, the nightmare of ensuring that updated certs for the keys get rolled out to all the devices so they don't all panic and say that the GPS isn't working at all anymore. For that, cell phones would probably be the easiest despite jerkass behaviour of manufacturers and service providers. Embedded GPS updating would be an absolute nightmare.
- jessriedel 8y agoOf course, celestial navigation doesn't work in the daytime. It also seem weird to write an article aimed at readers who have never heard of it, but not mention the existence of terrain contour matching, which is widely used on cruise missiles and works any time of day. https://en.m.wikipedia.org/wiki/TERCOM https://en.m.wikipedia.org/wiki/TERCOM
- oh_sigh 8y agoSure it does - consider that the sun is a celestial object. Sailors for hundreds of years have been shooting a noon sight.
- the8472 8y ago> Of course, celestial navigation doesn't work in the daytime. Even with a simple sextant you can use the sun. And the SR71's system did operate during daytime using starlight.
- deleted 8y ago[deleted]
- ams6110 8y agoI was wondering about that. I guess at the altitudes the SR71 operated at, at least the brighter stars would be visible.
- mycall 8y agoBoots on the ground could use laser communications to satcom for coordinate corrections, bypassing the locale drift, or better yet, retransmitting over the spoofed signal with higher strength.
- nradov 8y agoIt's tough to align a laser precisely enough to reliably hit a satellite. The necessary equipment is too heavy and fragile for ground troops. Plus it doesn't work through clouds.
- ckozlowski 8y agoNeat article. The Pentagon has been aware of this for a while now (though as I understand, the Navy only recently brought back celestial navigation into it's curriculum) but what's neat to me is how we might have had say, one backup method for navigation before falling back to manual methods (usually INS, which the U.S. was a leader in). But modern computers allow for pulling together a vast array of sources like the NAVSOP system described. One method I thought was neat: I play a lot of military flight sims, with my favorite aircraft being the AJS-37 Viggen from the 1970s. A lot of aircraft of this period used TACAN for navigation supplemented by INS for missions over friendly territory. But not the Swedes. They used INS, with fixes being made by the pilot using it's ground radar to identify features on the ground that would correspond on a map. The idea was that you'd program your flight plan into the computer, with your waypoints being say, a bit of land that jutted out on a coastline, or a bridge, or a tiny lake. When you're flying, as your approach the feature, there would be a little "+" where the feature should be, which may or may not have drifted. The feature would be visible on the radar, and since the pilot knew it had to be centered on it, he would correct the waypoint and skew it back onto the feature it should be on. That would then update the rest of the waypoints in the system, correcting the drift. This is modeled in the game, and so when I'm going to hit a target, I'll have a nav fix some 20-30km from the target as the actual thing I'm hitting might not be identifiable on the radar. But my INS will be corrected just shy of the target, and I can be reasonably sure it won't drift too much when I arrive in the area. We can hit points in darkness or poor weather with no visibility, no GPS, no night vision. It's not fantastic, but it's reasonably capable, and requires no outside input. The Swedes later added TERCOM to the jet in the 90s (same thing early models of the Tomahawk used to navigate) which means the INS drift is now largely corrected automatically, but if this for some reason isn't working (in the game you can perform a TERCOM fix anywhere, but in real life the amount of ground maps that could be stored was limited, so if you were wildly off course it wouldn't be able to match where you were), we still have the radar nav fix backup. Neat stuff. =)
- nippoo 8y agoThe maths behind this kind of fusion of different data sources is also pretty beautiful. Kalman filters (https://www.bzarg.com/p/how-a-kalman-filter-works-in-pictures/ https://www.bzarg.com/p/how-a-kalman-filter-works-in-picture...) are similar to the sensor fusion community what RNNs are to machine learning; simply stick all your data sources in with their uncertainties, and put pops a corrected estimate (in this case, position). It makes it much easier to combine data sources with rapid refresh rate but high integral error (IMU, gyroscopes, ...) with GPS/celestial navigation.
- ycombonator 8y agoI have always wondered which discipline is responsible for designing the rigs that various components are bolted on later ? Are there any online resources to learn this craft ?https://imagesvc.timeincapp.com/v3/foundry/image/?q=60&url=https%3A%2F%2Fs3.amazonaws.com%2Fthe-drive-staging%2Fmessage-editor%252F1514914884271-a19700234000d4.jpg https://imagesvc.timeincapp.com/v3/foundry/image/?q=60&url=h...
- KaiserPro 8y agoNow that storage and processing power are cheap and plentiful, there are a range of options for navigation 1) using visual keypoints ala https://scape.io https://scape.io 2) a much older idea, used in cruse missiles: radar contour mapping. 3) decca or loran 3.5) passive radar 4) inertial dead reckoning(sensors are much, much better nowadays). 5) laser painting way points. 6) multi spectral, multi viewpoint cameras with slam/visual odometery (with a database of coast lines for pinpointing land fall.) or better yet, a combo of all of them. The more data points the better.
- caycep 8y agoIT's funny how my understanding of warfare changes over time. As a youngling, it's all about sleek shapes and speed and boom boom (that may be a criticism of how society raises men as well). Now, it's more about how one side's nerds outthinks the other side in terms of sensors, data, etc. Even in the macho world of fighter planes (i.e. JSF and how everyone is thinking of detecting signals vs. hiding signals). It's a weird juxtaposition - the techworld and silicon valley's general ethos about changing the world, democratizing tech, etc, vs. nerds coming up w/ ways to better kill each other...
- Animats 8y agoThe USAF would prefer more accurate inertial systems. Modern bombing runs are often near the ground, not at high altitude where the stars are visible. DARPA is working on this.[1][3] They're trying to get MEMS gyros up to navigation grade, and funding work on something called "single atom interferometry".[2] [1] https://www.darpa.mil/program/adaptable-navigation-systems https://www.darpa.mil/program/adaptable-navigation-systems [2] http://web.stanford.edu/group/scpnt/pnt/PNT07/Presentations/14.%20Kasevich_PNT-Symposium.pdf http://web.stanford.edu/group/scpnt/pnt/PNT07/Presentations/... [3] https://www.darpa.mil/program/micro-technology-for-positioning-navigation-and-timing https://www.darpa.mil/program/micro-technology-for-positioni...