Rumoured "mini-nuke/diesel" Submarine SSK-N(?) thread

[FairAndUnbiased]

Swedish one is less powerful than Chinese one, so it is going to be smaller. And you want 6 of them. You also need machine that takes input from all 6 machines and output to your electric motor directly or charge battery. And you need a lot of rafting around that. There is no getting around space utilization on this.

Single steam turbine would just require rafting 1 turbine. It wouldn't be much different than how they would raft one on a larger submarine

I think we need an actual mechanical engineer to comment on this because this is detailed to the point of being something that you can't easily deduce from simple concepts.

 

[tphuang]

If you meant no SSN level dampening need, it is page 1. "Comparable radiation and noise level as conventional". Therefore SSN thick isulation is a drawback, not advantage. SSKN solved noise issue at root, so never needed thick insulations. Like a sick man dont brag to healthy man of his high quality medicine. SSKN should be as stealthy as SSK, if not more. SSK of same size is generally regarded as harder to detect than SSN at equal condition.

I'm talking about your statement "This is far stealthier than SSN. " There is no proof at all that SSKN will be far stealthier than SSN. There is a lot of assumptions here like "SSKN should be as stealth as SSK" or "SSK is harder to detect than SSN at equal condition". Where do these beliefs even come from?

If SSK is so hard to detect, why do you think PLAN has far harder time detecting USN SSN than JMSDF SSK?

I think we need an actual mechanical engineer to comment on this because this is detailed to the point of being something that you can't easily deduce from simple concepts.

a mechanical engineer would have no idea what level of rafting is needed unless he/she actually works in a submarine. And if that's the case, such information is confidential.

But it's clear that if you have stirling or steam turbine, it will make noise from spinning as a mechanical machinery. So that is additional noise which will need to be isolated and dealt with rafting. It would be entirely unrealistic to think that China would not try to do this.

 

[FairAndUnbiased]

I'm talking about your statement "This is far stealthier than SSN. " There is no proof at all that SSKN will be far stealthier than SSN. There is a lot of assumptions here like "SSKN should be as stealth as SSK" or "SSK is harder to detect than SSN at equal condition". Where do these beliefs even come from?

If SSK is so hard to detect, why do you think PLAN has far harder time detecting USN SSN than JMSDF SSK?

a mechanical engineer would have no idea what level of rafting is needed unless he/she actually works in a submarine. And if that's the case, such information is confidential.

But it's clear that if you have stirling or steam turbine, it will make noise from spinning as a mechanical machinery. So that is additional noise which will need to be isolated and dealt with rafting. It would be entirely unrealistic to think that China would not try to do this.

The noise spectrum of rotary machinery is very different than reciprocating machinery, the details of which can be deduced from general engineering concepts but which I am not familiar with.

JMSDF SSKs use diesels or transit at snorkel depth with diesels frequently. Diesels are very noisy as they are internal combustion engines.

 

[Xiongmao]

Anyone think it may be possible to use a thorium molten salt reactor in this? The high temperature might make the Stirling engines more efficient.

 

[tphuang]

The noise spectrum of rotary machinery is very different than reciprocating machinery, the details of which can be deduced from general engineering concepts but which I am not familiar with.

I don’t think you quite appreciate the level of stealth they are going for here. You need rafting around stirling

JMSDF SSKs use diesels or transit at snorkel depth with diesels frequently. Diesels are very noisy as they are internal combustion engines.

There is more to this. advanced nuclear subs are more stealthy than diesel subs in vast majority of scenarios. Which goes back to the original question on what type of capabilities you are trying to put on a mini nuke will determine what type of design to use. If you want to sustain 5-8 knots at lower depth indefinitely and also support atmospheric control, then you need to probably have a generator capable of 4-5 mw. I am just throwing this number out there to point out that it will need to be a magnitude higher than current aip technology. I have no idea what the actual number needs to be.

 

[Jason_]

I don’t think you quite appreciate the level of stealth they are going for here. You need rafting around stirling

There is more to this. advanced nuclear subs are more stealthy than diesel subs in vast majority of scenarios. Which goes back to the original question on what type of capabilities you are trying to put on a mini nuke will determine what type of design to use. If you want to sustain 5-8 knots at lower depth indefinitely and also support atmospheric control, then you need to probably have a generator capable of 4-5 mw. I am just throwing this number out there to point out that it will need to be a magnitude higher than current aip technology. I have no idea what the actual number needs to be.

The actual number seems to be on the order of ~2*75kW for conventional AIP (Gotland) and ~1.2MW for nuclear AIP. This is the number the original Twitter poster got assuming a 10 MW thermal reactor driving 4*320kW Stirling.

 

[FairAndUnbiased]

I don’t think you quite appreciate the level of stealth they are going for here. You need rafting around stirling

There is more to this. advanced nuclear subs are more stealthy than diesel subs in vast majority of scenarios. Which goes back to the original question on what type of capabilities you are trying to put on a mini nuke will determine what type of design to use. If you want to sustain 5-8 knots at lower depth indefinitely and also support atmospheric control, then you need to probably have a generator capable of 4-5 mw. I am just throwing this number out there to point out that it will need to be a magnitude higher than current aip technology. I have no idea what the actual number needs to be.

Yes but the type and size of rafting will be different. It all depends on the specific vibrational spectrum.

Atmospheric management is doable. It's just electrolysis of water to produce oxygen for breathing purposes. You'll need to produce 15 L per hour of oxygen per person.

A 1 MW electrolyzer produces 50 L/min or 3000 L/hr which is enough for a crew of 200.

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For a crew of 36 as typical on a 039A SSK, you would only need 540 L/hr of oxygen production which scales down to 133 kW. If that number is further cut, then you can get away with an even smaller electrolyzer.

 

[LuzinskiJ]

None of those are necessarily the case, assuming this mini-nuke is real and the descriptors of it are anywhere near reality.

1. It is impossible to talk about cost effectiveness if we cannot compare like for like. This mini-nuke (if it's real) will ultimately still be much slower than a proper nuclear submarine (even if it is faster than a traditional SSK), as well as displace much less and have less capable sensors, less volume for insulation and weapons and crew habitation facilities. In other words, you cannot compare cost effectiveness between two very different platforms.

2. We have no idea whether this supposed mini-nuke will be more stealthy than a proper nuclear submarine under similar operational demands/speeds/other characteristics.

3. We don't know how many mini-nukes will be procured versus how many proper nuclear submarines will be procured.


In other words, all three of these points are doubtful at best.



Instead of viewing the "mini-nuke" as being able to do the roles of a proper nuclear attack submarine "but smaller, more cost effective, and better in every way," you should probably view the "mini-nuke" as a "SSK but with longer endurance".

What if they were unmanned?

 

[BoraTas]

The actual number seems to be on the order of ~2*75kW for conventional AIP (Gotland) and ~1.2MW for nuclear AIP. This is the number the original Twitter poster got assuming a 10 MW thermal reactor driving 4*320kW Stirling.

Stirling engines running on a reactor's steam started to make sense. A Stirling engine of that power level could have an efficiency over 25% even at low temperatures. No steam turbine is reaching that efficiency at this scale. Rankine cycle applications running with organic fluids (ORC) are deemed better at the temperature and power level we are talking about here. Still, they don't touch 25%.


If we assume a 120 kW hotel load, 150 kW electrolyser load, 100 kW reactor safety load and 95% efficiency in the handling of electricity it means a 400 kW electricity generation load on the engines. This leaves 880 kW for propulsion. With the usual efficiency losses, we can guesstimate that the sub will have net ~590 kW pushing it forward. How good is this? It is actually plenty. Net 350 kW is enough for pushing a 3000 ton sub at 10 knots. I guess you could push a 4000 ton sub at 11 knots with 590 kW. That is a great level of performance. Closer to an SSN than an SSK.

Most of the numbers on this message came from this study and they are quite pessimistic. The study is on an SSN with an extra fuel cell AIP system for emergency load and extra-silent periods.

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[Blitzo]

What if they were unmanned?

Rofl let's not add further complex technologies on top of an already speculative and novel platform.

Really there are some questions which just shouldn't be asked yet.