China makes advances in laser-propelled submarines | Hacker News Reader

China makes advances in laser-propelled submarines

scmp.com

12 pointsnitin-pai18 comments

It's worth pointing out that this is authored by Stephen Chen who is a bit of a joke in defence news circles with a never ending supply of articles about how China has all these amazing weapons and technological advances that render the US helpless in comparison and there is one every few days or so. https://www.scmp.com/author/stephen-chen

That’s scmp for you.

This seemed like science fiction to me, but aparently it is real, the technology was introduced in a 2009 paper cited 20 times https://www.worldscientific.com/doi/abs/10.1142/S02179849100...

> Design can produce almost as much thrust as a commercial jet engine,

But does it have as much thrust as a normal submarine engine?

According to the article this uses plasma explosions and a working medium of metal particles.

Wouldn’t both lead to easier traceability (sound, metal)?

In comparison to conventional nuclear sub this method would be much quieter. But also much faster over long distances. You have two issues with subs, stealth and positioning. If you know, or have high confidence, that a combatant sub force is in X pos, and have Intel on its AVG speed then you can plan accordingly. Tech like that described above means a sub force can be more quickly repositioned, or deployed. You have Intel that X vessel was docked two days ago? Well it could be in the south pacific today.

One thing to keep in mind, there is a reason this is published publically. PLA want this out there for a reason, either to sow worry and concern or to mislead.

> this method would be much quieter

Source? Cavitation on propellers is a major source of uncloaking. This sub sounds fast but traceable—perhaps more ideal for a weapon than a vehicle.

The method described in the present article doesn't rely on rotating propellers that produce vibrations, thereby reducing one of the major sources of noise.

> method described in the present article doesn't rely on rotating propellers that produce vibrations, thereby reducing one of the major sources of noise

The main source of “hull vibration and noise” from propellers is cavitation [1]. Laser propulsion directly cavitates.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4549849/

It sounds like it's basically a gigantic cavitation noise generator, so yeah, I'm not imagining that it could possibly be quieter.

Today's submarines go to great lengths to avoid cavitation for just that reason.

Typically there's a velocity beyond which the vessel does not go if it wants to remain stealthy, as going faster than that drastically increases the cavitation noise.

The very end of the article talks about "green shipping" but it seems like this propulsion method would produce crazy levels of heat. Wouldn't that have adverse impact?

The whole bubbles and pulsing doesn’t sound particularly silent

Yeah, if I'm understanding what's going on here, it's going to be noisy as hell.

Cavitation noise isn't the only factor making a submarine detectable, but it's definitely high on the list. It's been used to detect submarines since WWII or thereabouts.

Maybe it's a variation of a https://en.wikipedia.org/wiki/Pump-jet somehow using lasers instead of impellers to heat the inflow all internally and dampened/mostly silenced to the outside? Also enabling https://en.wikipedia.org/wiki/Supercavitation by emitting some of the 'exhaust' from the tip of the bow?

It says its using lasers to vaporize seawater all around the submarine which would create a submarine sized super cavity which would have very very low resistance. The problem is what happens when the bubbles collapse. That's what causes the cavitation noise, its when the bubbles collapse. They can do so with such force that they can pull metal out of nearby surfaces.

Yah. Meanwhile elsewhere people have torn apart the news. Seems that it is just a concept, no test in reality at all, not even parts of it in a lab. Maybe late april joke?

It felt like I was reading from 'three body problem'. I wonder if the author was inspired by the sci fi there.

Wow that is super awesome and could be used for underwater weapons as well.

In combination with propellers for quick acceleration it should work too.

Reply on news.ycombinator.com