Hacker News Reader

Naive suggestion from someone who has zero knowledge about these things: can't an unmanned submarine drone be constantly moving ahead of the main submarine to detect these obstacles before they become dangerous to the submarine and crew?

Yes, but noise would be a problem.

Noise from the drone propeller?

Wouldn't a small drone make less noise than a submarine?

That seems intuitive but one thing I've learned in my career is that obvious easy ideas that nobody does are usually missing key details.

A small drone and a submarine would make more noise than either alone.

What about using a pressure sensor fixed to a long pole in front of the submarine? That way, if they hit anything, the pole would hit first, and could activate the stopping mechanism.

These things can't stop on a dime.

How long would the pole have to be to stop a 40mph submarine?

You could probably find the data you need here:

https://core.ac.uk/download/pdf/36725639.pdf

Imagine swimming with a long pole attached to the front of you. Even if it would be thin, it would still disturb you very much. Also the disturbances in the water created by the pole would make noise, that can be detected.

Submarines are optimised in everything for absolute stealth, up to the point that the crew may not make any noise, like dropping a wrench.

Best solution is to pre-map the ocean to the degree possible (mountains don't tend to move, at least on the timescales we care about...); this wouldn't need to be done stealthily (so you could use active sensors), and using surface ships is one option, also drone surface ships and drone underwater vehicles now. I assume there are relatively highly classified high-detail government maps of certain parts of the ocean of particular interest.

We also have highly classified models of the exact shape and mass distribution of the Earth, as this is essential to accurate long-range ballistics (i.e. for ICBMs to hit their targets) -- it affects the gravity experienced over the course, and the precision/accuracy needed is higher than just uniform-density sphere or oblate spheroid. Also of magnetic and other anomalies since that can be used as a baseline when searching for submarines or ships using magnetic sensors, although I think this is less important now.

How many decades/centuries would it take to map the ocean?

It sounds like the Human Genome Project. Well worth the effort.

Its already been largely done, which is why when subs run into seamounts, you tend to see the leadership team relieved.

“Maybe it would help to have a map of the space we’re going to be driving very large, very expensive, strategically important pieces of equipment (that also have crews) through blind” is not, as it turns out, something that never occurred to the Navy.

Oceans cover 361M km^2. So if we built 13,333 drones with a failure rate of 25% and they map at a rate of 50 km^2/day at a higher column depth with active sonar, it would take approximately 2 years

https://www.youtube.com/watch?v=83FQzfH_r2U

There you go.

Also don’t need to do the entire ocean; there are specific routes and zones we care about the most, can easily prioritize those.

Indeed. It can certainly be accomplished.

https://seabed2030.org/

Project goal is 2030.

How would it communicate stealthily?

It wouldn't because it wouldn't be stealthy.

Why does everyone assume you need wireless communication? You can have a cable running between the submarine and the drone, same channel would be used to power the sub.

Like a Medusa. Submarines would get scarier.

That is a lot of heavy, droopy, cable (if it is going to be able to withstand the stresses and ‘unkindness’ of the ocean) which is very likely to get tangled in things like spinning propellers unless very carefully managed.

Also, fishing trawlers, whales, etc.

Even worse than letting an enemy know where you are now, is letting them know where you will be in the future.

Also speaking from utter naivety, this seems like a super good idea. Each submarine gets a little attendant constellation of drones. Control them with Bluetooth. Or usb cables.

Or whiskers! That's how cats and catfish do it. A dozen 300' plastic prongs protruding frontward.

Or, to combine the two : TENTACLES!

Nice idea, but how many ship-lengths does a submarine need to slow down from full to zero speed? Probably more than a few.

The submarine in SeaQuest DSV had mini underwater drones called whiskers that did this job:

https://en.m.wikipedia.org/wiki/SeaQuest_DSV

I recall looking at the various charts and from what I recall the "discolored water" notation was sourced from a chart several decades before and was offset by a few miles (incorrectly charted in the first place).

>> Are light, radar, and sonar still not enough to detect obstacles that big?

> Radar is useless underwater, light would also be useless for spotting anything in time to react at speed, and sonar isn’t routinely used because it compromises stealth.

Any people with knowledge in the field care to comment on whether it's feasible for a light (em?)-type, active, near-range detection system to work?

It seems to me the basic problem is:

- enough energy to get a signal at a range sufficient to move around any detected obstacles

- high enough dissipation in water to minimize range at which detection by external sensors is possible

The light transmission through the water, it's cloudiness, is just way to variable for something like this to work constantly, reliably.

Wouldn't the cloudiness itself be a signal?

Presumably it's essentially clear of suspended particles, most of the time.

A signal of what?

Something solid ahead

To clarify: I mean that, generally speaking, the presence of 'cloudy' water would presumably signify that the seafloor was close. In the open ocean, maybe a sea mount is surrounded by essentially a cloud of particles.

Edit: I think your reply made the thread reach maximum depth, so I'll end it here.. I should do more reading on the topic.

The problem I'm highlighting is it also gets cloudy randomly in open ocean, for lots of other reasons.

The issue is that the cloudiness of water, even open water, varies greatly. So there would be either lots and lots of false positives, or the system would be too insensitive.

Think driving in fog

Have you ever dived? Max visibility is like 30-50m unless you’re in a filtered environment

Your two requirements contradict each other. You can choose one or the other, but not both.

The world's militaries have invested a great deal of time and money into researching underwater sensors. The solution is not going to be discovered by random people on the Internet.

> The solution is not going to be discovered by random people on the Internet.

I'm fairly certain someone knows a number of things that have been discovered by random people on the internet.

Water absorbs photons at most frequencies outside the visible spectrum. What we deems as visible light is actually where water is most transparent. Since eyes evolved underwater, it makes sense they would use this section of the spectrum.

https://commons.wikimedia.org/wiki/File:Absorption_spectrum_...

That makes so much sense and actually unravels a few other mysteries for me. Thanks!

> Any people with knowledge in the field care to comment on whether it's feasible for a light (em?)-type, active, near-range detection system to work?

I’m not in the field, but I follow it enough to say: in theory, yes, (blue-green lidar), and there is a lot of work on moving this from theory to practice.

But approximately everyone is working on it (for bathymetry and for detecting subs, and similar blue-green laser tech for underwater comms), so its likely once its deployed so that a sub could in principle use it as a “headlight”, it’ll raise similar concerns to sonar, because if it is used actively, passive sensors looking for active use will also be common.

the issue is to detect these while maintaining stealth.

> and sonar isn’t routinely used because it compromises stealth.

Can't they use the same frequency/waveform as whales?

Or a different question: why don't whales routinely hit underwater volcanoes?

Couple of different answers to these questions:

a) whales don't tend to go where volcanos are. Whales dive to find food, and their food sources aren't near the seabed. I think the deepest diving whale species are sperm whales, and they go after squid, which are not typically found near volcanos.

b) it's not a question of matching frequency with the whales, it's a question of noise emissions and the amount of energy you're putting into the water. Modern active sonar systems are incredibly energy intensive, and the technology to modify the waveform and limit the power of the waveform to match something biologic doesn't really exist, and would have to justify all the added complexity

c) USN and US geological survey charts are really really good, and regularly updated, to the point where "It wasn't on the charts!" is a claim met with extreme skepticism. 9 times out of 10 some sort of navigation or systemic error was involved.

"Radar is useless underwater."

But sonar and detecting changes in gravity (caused by the higher density of the seamount) aren't.

The seamount should have been detectable.

There's no way you could have gotten a gravity sensor to work reliably enough in that environment. Active sonar would defeat the point of a stealth submarine.

Is that an assumption or do you know from fact?

Gravity detectors work from moving aircraft (it's a common method of deployment), so motion's no problem and can be made incredibly sensitive—sensitive enough to suit the job in hand (place one on a table and then on a book on the table and you'll easily read the difference in gravity). Moreover, seamounts are incredibly large objects and would have huge signatures and thus easy to detect.

I'd suggest the real issue around this matter is that it'll be classified.

What's the technical term for this type of gravity detector? Do you mean a gravity gradiometer? It seems hard to steer a modern pigheaded search engine away from LIGO when you search for "gravity detector".

Gradiometer as here: https://www.sciencedirect.com/topics/earth-and-planetary-sci...

We'd have difficulty in fitting LIGO in a sub methinks and seamounts are static and thus no G waves. You're right though, I should have been more specific, perhaps a more understandable description would be a mass detector or sensor.

I reckon the reason we don't hear much about this subject and the reason it's likely classified is that's its primary purpose would be the detection of other subs, detecting seamounts a secondary benefit.

Interesting, thanks. It didn't occur to me before that there might be classified work on gravity detectors.

Sonar is a brilliant beacon identifying the subs location; other than in combat where they are already detected or desperately need a hard fix on a target now, or someplace they don’t need to be stealthy, subs aren’t using it.

AFAIK, the first sub-deployed gravity gradiometers were developed for the Ohio-class ballistic missile subs and Los Angeles-class attack subs like San Francisco don’t, AFAIK, have them.

> Hitting a mountain is generally because the mountain wasn't on the chart being used

How could it not be in the chart though? Is the ocean not fully mapped?

No, the ocean is not fully mapped. It's written in the article: "With only one-quarter of the sea floor mapped with sonar, it is impossible to know how many seamounts exist."

> How could it not be in the chart though?

In the specific case of the San Francisco, because notations indicating a probable seamount were not transferred from other charts when the chart being used was compiled; there is some lack of clarity on how much the failures involved are the responsibility of the command crew of the sub and how much of higher command, but its definitely a failure to appropriately use existing information, not a “the information did not exist” problem.

While the area was apparently not well charted, the responsible crew not using the information at hand (including information as to the the quality of charting data for the area) was also apparently at play in the Connecticut grounding.