Ask HN: Why is there no GPS in the ocean?
I'm not an electrical engineer so please forgive my ignorance. I guess I could just ask ChatGPT but figured there may be a more interesting response here. Why can't the ocean have something like GPS? Also, if a nuclear submarine (those ones whose exact positions are classified) identified the location of this submersible, would they tell the relevant authorities? Or would they not, in order to protect their classified sensors and position? The ocean can’t have GPS because GPS relies on time of flight calculations for radio waves (aka light) traveling at the speed of light through air. The ocean, to the surprise of many, is not composed of air, and is really, really, exceptionally good at scattering light. What you could have, instead, is an acoustic positioning system that would rely on fixed transponders that would allow time of swim calculations for sound waves traveling through water. This would be phenomenally problematic, as you’d need a near perfect understanding of confounding factors like salinity, temperature, depth, etc to accurately model the incoming reply… you’d also drive the whales and fishes to consider well justified total warfare against the really loud and insensitive terrestrial creatures they vastly outnumber. GPS works on the surface of the ocean. But the radio waves cannot penetrate water very far, so it fails if you are submerged (few things can which is why subs are so well hidden compared to aircraft. Unless a nuclear sub was specifically sent to the area to look, it is very very unlikely to just be "in the area". Even if it were there, it is very hard to find a small metal box on the bottom of the ocean. There is no real sensor for that. Most military subs are not designed to dive beyond about 500m depth (there is no need, 100m is more than enough to be functionally undetectable from the surface). The titanic is at about 3800m. So they likely could not get anywhere near close enough. GPS is a one way system. A GPS receiver can only tell where it is, it does not transmit its position. To transmit position you would use a EPIRB. A EPIRB however cannot work underwater as its radio signal would be blocked by the water just as a GPS signal is blocked. They are looking for this submersible by sonar. You don't need a nuclear submarine for sonar as it can done with ships ,sonobuoys dropped by aircraft or RV subs with sonar. These are all good answers by the way thank you. Isn't there like an "emergency transponder beacon" or something (like aircraft have?) that ships and submersibles must have? Why can't this be used? That’s what the EPIRB is… problem is it has to reach the surface to broadcast; they’re designed for finding floating vessels / life boats, not submerged objects (in this case, tombs). To be useful it would need to be spooled out on a VERY long line that you could follow back down. In this case that means the EPIRB would need to be buoyant enough to float both itself and 4000+ meters of heavy line … which would be great, although also a threat to navigation. Isn't there a way to use the charge conductivity of water to send a signal--like "electrolysis radio"? Alternately it seems a constellation of cheap radio beacons / high powered IR reflectors, that can float to the surface at a constant rate in event of emergency. So you basically end up with a 2D surface trail of reflectors laid over time since the incident. That should be somewhat helpful to pin down a search area, I would imagine, without relying on a single one, or having a long spool line. But I don't know for sure, just spitballing. Those poor people :( People have been spitballing on this problem for generations, and that latter one’s been tried too… problem is it’s effectively the same thing as trying to pinpoint a diver by her bubbles; if she’s near the surface, works great… if she’s 4KM down then the bubbles hit the surface spread effectively randomly over hundreds and hundreds of square kilometers, and usually kilometers off horizontally. The best way to maintain communication with a submersible is a tether. The best way to know the position of a submersible is a tether. The best way to raise a submersible in trouble is a tether… this company chose to go another way. And, let’s be clear, even if they knew precisely where it was the odds are very good that they couldn’t possibly effect a rescue. The grim truth is that everyone aboard is already dead, the hope is that it was a sudden implosion rather than slowly freezing, drowning, or asphyxiating. You were right man! Tragic. I'm hoping you're a navy insider and can feed us interesting tidbits about UFOs. Any stories? Do you know how the Navy detected the anomaly? Was a ship nearby or was it their monitoring grid? It's good they informed everyone--I had a feeling they definitely knew what happened or would be the ones who would find it. Not Navy, just did some technical diving when I was younger. Most likely the signature of the implosion was picked up by the old fixed hydrophone arrays that form the backbone of submarine surveillance. It would have been like a really loud thunderclap as about 20 cubic meters of interior volume (and 5 people) tried to instantaneously squeeze into 0.05 cubic meters (about the space 2/3rds of 1 human usually occupies)… odds are hydrophones were still picking it up hours later and thousands of miles away. And yeah, they knew pretty quick that a sound consistent with an implosion was heard at a time consistent with the loss of communication… not entirely sure why there wasn’t more communication of that earlier, though. Probably some fairly rich constituents pushing on the political side for a showy (and costly) rescue attempt that was always going to end up being a salvage and recovery operation. Now that the engineering choices have become clear it’s no wonder this happened… they really had “disrupted” their way into a time bomb. Cool, thanks! Technical divings, sounds like using gases and specialized stuff. I wonder why you did that, just for fun? Pretty interesting anyway. :) I was in Vancouver, BC at the time, and all the diving that wasn’t just wading in from shore was technical, due to the depths and the temperatures. So drysuits, nitrox, argon bottles for insulation in the cold, that sort of thing. It’s a fascinating world, but that time I had to do an emergency, no-air ascent from pitch black 110ft down after an o-ring snapped in my regulator kind of told me it wasn’t a life-long hobby. Wow man, that’s impressive. Kinda makes me want to try it all the more now. Is that crazy? Adding some points: Radio waves (very high frequency) of GPS cannot go deep in the ocean. Very low frequency can, but their wavelenght is very big, so unsuitable for a GPS.
The only ways to "see" undersea are acoustic and magnetic.
Nuclear sub navigation rely on inertial systems, and i think they can give a position to civilians for rescue.