I'm particularly interested in an educated perspective on their choice in materials. I'm familiar with carbon fibre from bike frame building, and the common tricks/practices to try and look for fissures, find voids/delaminations, etc. after a crash, and it's such a complex subject and material. I wonder who manufactured this vessel and what the quality of their facilities, tools, processes was.

Do you think they do extensive trial runs first at the beginning of each season? Like send it to the bottom un-manned just to double check?

As my former boss liked to say "Things that aren't tested don't work."

We've got more than enough ways to rig up signalling networks that there is zero reason for any submersible to not be remotely tested to crush depth.

Carbon, as you correctly note, needs to be very homogeneous. Bubbles, lamination defects or -god beware- fissures lead to failure, of the sudden, unannounced and total kind. And not only is it necessary to check after production, but also after regular short intervals of use, because a mere scratch in the carbon can be fatal.

The advantage of CF is low weight. But who cares what a submarine weighs?

Some of the articles about it's construction indicate that many of the engineers were aerospace engineers.

I wouldn't want a submarine engineer designing a plane, and vice versa.

Apparently the idea was that a lighter sub could be more easily and cheaply deployed around the world without needing to rely on a large, expensive support ship with heavy-lift capabilities. [1]

Basically, it was a cost-cutting measure.

1: https://www.smithsonianmag.com/innovation/worlds-first-deep-...

The heavier a sub is the bigger the ballast tanks have to be to compensate and the more energy is wasted on moving it, just like any other powered vehicle.

The biggest benefit of reduced weight on this thing would be minimizing the size of the crane and surface vessel needed to deploy and recover it.

I even get worried about cracks in my road bike. These guys are going 3km+ under water... It's insane.

Here is a quick and dirty analysis from a US Submariner of 20 years.

It is supposedly, incredibly hard to find defects or damage on carbon fiber. SpaceX did cite this as a reason for using stainless steel. His belief is that there was a hull failure somewhere on the carbon fiber hull; a failure point that simply wasn't found before this dive.

If there were relevant changes to the new model other than scaling it up, it'd need to go through a much lengthier certification and testing phase.

People died. I do hope the CEO isn't one of them, because he needs to be thrown in front of a court. Same with the other senior executives and HR.

I think occams razor suggests that they experienced a breach or defect in the viewing window (or possibly the hull).

At the pressures they were at, it would have been over for them, before they ever even knew there was a problem. The pressures are so great, that they would have assimilated into the water instantly.

For what its worth, as sad as that sounds, it is possibly a better fate than the alternative of suffocating to death for 4 days in complete darkness (which is exactly what happened to 23 crew members aboard the Kursk russian sub back in 2000 [1])

[1] https://en.wikipedia.org/wiki/Kursk_submarine_disaster

"Analysts concluded that 23 sailors took refuge in the small ninth compartment and survived for more than six hours. When oxygen ran low, they attempted to replace a potassium superoxide chemical oxygen cartridge, but it fell into the oily sea water and exploded on contact. The resulting fire killed several crew members and triggered a flash fire that consumed the remaining oxygen, suffocating the remaining survivors."

Time isn't on their side.

Official reports have been saying 40 hours a few hours ago.

It has come out that it is wildly untested and optimistic estimate. The longest mission they had conducted onboard was 12 hours. So the theoretical limit may not be realistic. If there was panic onboard, that would increase oxygen usage dramatically, which could cut as much as 25% off the estimate (which is nearly a day in this case).

In other words... it is grim.

They were early enough into the dive that they would have abandoned the dive after losing contact, they would have only been about halfway to the bottom, and they still would need communication to even find the titanic. So if they lost contact, the mission would have been aborted inside the sub, because they wouldn't have any hope of completing the mission without the aid of the surface vessel.

There are several emergency surfacing options available on the sub in addition to the primary propulsion method. If the sub lost contact, it would have surfaced. That is what happened in several other missions this company has made where communication was lost.

So the fact that communication was lost and no attempt to surface was made, suggests that there was a catastrophic failure. At the pressure they were at, the smallest leak would lead to immediate implosion. The most likely scenario is that they experienced a crack or defect in the hull that lead to implosion. It was likely over before anyone onboard even was aware of a problem (or within seconds of it).

Not if they are doing something useful to others.

Are hikers who get lost on a mission?

    (1) a specific task with which a person or a group is charged
    (2) a definite military, *naval*, or aerospace task

You should seriously find better things to do with your life than obtuse rebellion against dictionary definitions. It makes you look like an illiterate nonce.

[1] https://www.merriam-webster.com/dictionary/mission

If they are on the surface, getting them by sonar is not possible, but aerial surveillance might find them. However, things are very hard to see in the ocean if there are waves. They might have an AIS locator which would transmit their position and an emergency signal, but maybe they skimped on that too, because the submarine-rated ones are expensive.

Volume is also an issue, the Titan is far smaller than a military sub, so the sonar spike corresponding to the implosion will be shorter and of a smaller amplitude.

The sonar on their surface vessel should have picked up the noise, if they have one that does recordings and passive mode. But I guess they were too cheap for that as well, since no regular sonar surveilance of the sub is mentioned in the press.

Failure is going to occur on the order of fractions of a second at those huge pressures. (Fortunately?)

Here's a pressure vessel failing at only 1 bar:

https://youtu.be/Zz95_VvTxZM

Perhaps there might be a hairline crack that makes a window shatter when it's hit with a hammer. Except the hammer impact is constant. I don't think there would have been a lot of time.

Press against a solid object gently with one hand on each side, then suddenly yank away one hand. The object will be accelerated gently. Now do that with all your strength and send the object flying through the room in no time, with a few dozen kg of pressure. Now imagine that you could apply hundreds of tons of pressure. In such a system, every change will be nigh instantaneous.

That would imply a collapsing somewhere between the two.

Also, would the body, being mostly made of water itself, really get crushed instantly? I would certainly expect the pressure to squeeze all the air out of your lungs.

I know nothing about how the body behaves under high pressure.

"psi" is pounds per square inch, and a human has ballpark 3000 square inches of surface area.

So to get a (very) rough approximation, picture what would happen if you squeezed a human with 3000*1892 pounds of force. Or try not to picture it, because I imagine it being pretty gross.

Industrial divers / welders / etc get all kinds of training to avoid that stuff, for good reason.

That said, if divers are slowly "eased in" to the high pressure environment, it is actually possible to equalize pressure slowly and acclimatize. Though 1.3km would still likely be beyond the limits of that https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5110125/

I'm blown away that for a sub of that size and shape they used carbon fiber. The sub is positively gigantic and a cylinder is very susceptible to failure after repeated cycles. I'm pretty sure the claims they made about working with NASA and having a system to monitor the structural integrity of the sub are just BS.

"Hi Bob, did you used to work at NASA in the 60's? Can I ask, do you think this 1/100th scale submarine could get to this 1/100th scale titanic in my bathtub? kthxbye"

It took a while to go from dismissing employee concerns to tourism, but it seems to be the same device.