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What If GPS Stood for “Galactic Positioning System”?
- ukulele 9y agoIn theory this is a much better approach than Earth satellites: the farther away an object is, the smaller its motion will appear. With hundreds or even thousands of "fixed" data points incoming, it should be possible to develop an incredibly accurate model for position in space.
- fooker 9y agoI suspect the latency might kill this idea.
- baseethrowaway 9y agoNot at all, if you take it into account.
- fooker 9y agoWould you be happy to wait for tens of minutes to get a position lock?
- handedness 9y agoOne wouldn't be transmitting to pulsars and awaiting a response, but treating them as what they are: always-on beacons. The signals would always be present.
- lorenzhs 9y agoNot even GPS transmits to the satellites, it only relies on observations of what the satellites sent. And pulsars are quite a bit further away than tens of light minutes :) Mars is currently 14 light minutes from Earth. PSR J2144-3933 is one of the nearest known pulsars, and it's some 587 light years away.
- pc86 9y agoYes but if we're using it as a beacon the distance is irrelevant, isn't it? It's been "transmitting" for much longer than 587 years, we're already receiving a signal, and that's what we're using?
- lorenzhs 9y agoExactly. The post I replied to said "One wouldn't be transmitting to pulsars and awaiting a response", and I expanded on that. The whole subthread of https://news.ycombinator.com/item?id=16288955 https://news.ycombinator.com/item?id=16288955 doesn't make much sense because nobody defined what they mean by "latency" and people are talking about different things.
- misnome 9y agoTens of minutes to get a position lock for your location in the entire Galaxy? Yes, that sounds completely reasonable.
- thaumasiotes 9y agoOf course, if that was the best I could do. People will happily spend an entire day becoming unlost if they're lost. As long as they have the means to survive, they'll be willing to spend much longer than that.
- Maken 9y agoLikely, after the first calibration you could keep moving around and updating your location, so as long as the system doesn't go down you always know your (relative) position as you travel through the galaxy.
- ccozan 9y agoI thought of this as well. After the first lock, you can use inertial navigation.
- kijin 9y agoRegular GPS does this, too. It takes about 12 minutes to download the list of currently active satellites and their attributes. The data is part of the signal from the satellites. Most GPS units do this in the background. But if you leave it unpowered for too long, it will need to update itself before it begins to work properly. The GPS in my dad's car used to have a flaky ROM, and it would show the car flying across the wilderness at over 400mph while it was updating.
- emiliobumachar 9y agoIf I can then keep the lock indefinitely, I don't see much of a downside.
- tlrobinson 9y agoYes, especially if it’s just to occasionally recalibrate an inertial guidance system.
- Lewton 9y agoWhat latency? They're talking about measuring millisecond pulsars, there's no latency
- TheOtherHobbes 9y agoIndeed. But if you're travelling significant distances, you're not going to be able to assume the space between you and all your beacons is flat. For good accuracy you'd need a predictive spacetime curvature map for the entire galaxy, and that might not be an easy thing to generate.
- solotronics 9y agoit would probably be an advantage to measure the shift effect from multiple sources as you travel whatever fraction of the speed of light, giving both your position and derivatives such as velocity
- widdma 9y agoThis is exactly what is already done! On Earth at least. Radio telescopes around the world observe (mostly) quasars to perform geodesy. This is the main method used to measure the Earth Orientation Parameters which is need for keeping GPS/GNSS calibrated. With it, you can measure distances of several thousand km with a precision on the order of a few millimetres. The problem is that it's really expensive compared to GPS: at each site you need a reasonably size telescope, atomic clock, some serious storage, and a way to ship all the data to a central cluster.
- nitwit005 9y ago> That pulse was emitted long ago from the distant pulsar and then spread outward through space. If you knew the exact time was when it was first emitted and the exact time you had received it, you’d be able to deduce how long it had been flying through space. Dividing by the speed of light would provide you with a measurement of your distance from the pulsar. Am I missing something here? It doesn't seem like you can know the time emitted if you don't know your position.
- Dylan16807 9y agoYou'd calibrate the timing of the pulsars before launch.
- baseethrowaway 9y agoWhich means that you would have to keep track of each pulse, if you have a comparatively inaccurate clock. Does not seem practical. EDIT: On second thought, using an accurate clock would be a tiny fraction of the cost of the whole system, so it's a solved problem.
- pc86 9y agoTIL using multiple pulsars to create a galactic positioning system "is a solved problem."
- toomuchtodo 9y agoThere’s a washing machine sized pulsar detector bolted to the International Space Station that is successfully locating itself with pulsars. https://www.nasa.gov/sites/default/files/atoms/files/session_3_-_2_x-ray_pulsar_navigation_for_deep-space_autonomous_applications_jason_mitchell_0.pdf https://www.nasa.gov/sites/default/files/atoms/files/session...
- Dylan16807 9y agoThough it's useful, you don't even need an accurate clock. You can observe the relative phases of several pulsars to recover your clock.
- adynatos 9y agocould we use this on earth in the future?
- jannic 9y agoJust a guess: In priciple, yes, but it wouldn't be very practial. Because of noise sources on earth, one would need very big antennas pointing to the pulsars to get good s/n ratios. Additionally, as x-rays are blocked by the atmosphere, one would be limited to longer-wavelength pulsars, again increasing the size of the antennas. Given that, using GPS, we already have a positioning system much more accurate, I don't see why one would use pulsars for positioning on earth.
- tomalpha 9y agoIt does, perhaps, have the advantage of not needed a satellite fleet to work. So therefore isn’t at the whim of said fleet’s owner, or someone with anti-satellite missiles. (Granted that the antenna size problem might be a killer)
- gambiting 9y agoStar trackers do exactly this, providing relatively accurate positioning without GPS: https://en.wikipedia.org/wiki/Star_tracker https://en.wikipedia.org/wiki/Star_tracker
- oceanswave 9y agoWas going to say this, and in use by things like submarines and ships since the 60’s
- MayeulC 9y agoI was about to suggest the use of a sextant for this. As far as I know, navigators are still trained to operate them in this day. Of course, the same operational principle can be integrated into a dedicated device.
- 9y ago
- IanCal 9y agoThey say it took 8 hours, what's the cause of this? Does it take that time to locate and measure the pulsars? Or is it more signal processing time? Also - the idea of a pulsar spinning a thousand times a second is just incredible.
- xtf 9y agoHad to enable too much 3rd party scripts and other resources to read it. htetm;dr? Had to enable too much; didn't read?
- severine 9y agoUse this wonderful, underrated browser extension: https://firefox.add0n.com/reader-view.html https://firefox.add0n.com/reader-view.html edit: Not to be cryptic: > "Open In Reader View" adds a new context menu item to the page and link context menu to let you open webpages and urls directly in the reader view mode to strip away all of the clutter. Ignore the domain name, there's versions for Chrome and Opera too!
- viach 9y agoInteresting, this is probably the right approach to searching for the aliens civilizations. These guys should have globally visible intergalactic GPS, we just have to imagine how and where they would put the searchlights, the most effective places.
- fooker 9y agoWhat if these pulsars are their 'GPS satellites'?
- viach 9y agoThere should be some logic. Someone should create a project of this imaginary galactic GPS infrastructure, taking into a count all the details - potentially limited resources needed to build it, maximum visibility, distances coverage and then compare it to the map of these pulsars. And if there is bingo or sort of, we could get the space points where to rearrange our radio telescopes to listen to.
- fooker 9y agoI can imagine some kind of optimization problem, the solution for which would be the ideal locations for these bodies. Unfortunately I do not understand enough physics to give a concrete problem.
- samfriedman 9y agoHow quickly, on an astronomical scale, do pulsars slow down? I'd imagine that eventually the changes in rotation would throw off the positioning, and require recalibration. And of course eventually they'll stop being useful altogether. One would hope a civilization is able to create artificial pulsars by that time, however...
- blauditore 9y agoWikipedia mentions a life span of about 10 million years. If they slow down in a predictable way (exponentially?), navigation system could just calculate that in. And when some pulsars die out, new one have probably emerged in the meantime, allowing a smart-enough system to gradually switch sources.
- planteen 9y agoThe M1 (Crab Nebula) pulsar slows by 38 ns per day. But it is very new, less than 1000 years old. https://en.m.wikipedia.org/wiki/Crab_Pulsar https://en.m.wikipedia.org/wiki/Crab_Pulsar
- extrapickles 9y agoThats almost 1.6ns/hour. If you have a stable oscillator you can compare them to compute the time/date.
- deleted 9y ago[deleted]
- nerfhammer 9y agoWouldn't it depend on what happens to show up in the accretion disk? Including the life cycle of any companion stars? I would imagine that it's normally stable but less predictable perturbations can't be strictly ruled out.
- maniacalrobot 9y ago... And here I was thinking all you needed was six points of reference, and seventh point for the origin