> The company said that the sub has multiple forms of ballast, including systems that could be activated manually, and ties that were designed to dissolve after 20+ hours in seawater, allowing the sub to rise even if the crew were unconscious.

is there more information on these dissolvable ties? or their redundant ballast systems?

From David Pogue's report on his trip in 2022:

https://unsungscience.com/news/back-to-titanic-part-1/

Excerpt from the transcript:

But what if the hydraulic system breaks? Well, then they have roll weights.

KYLE: Ah, so, we’ve got these weights here on the side, these are roll weights, we can actually roll the sub and those come off, and that gains us some buoyancy to come back to the surface.

These are pipes that sit on a shelf that juts out from either side of the sub, held in place only by gravity. If everyone inside the sub shifts their weight to one side, the sub tips enough to let these pipes roll off.

If that doesn’t work, there are ballast bags, full of metal shot, hanging below the sub.

KYLE: These bags down below, we drop those off using motors and electric fingers.

OK. But what if the electronics go out, and the hydraulics fail, and everyone inside has passed out unconscious?

KYLE: There’s fusible links within these that actually can dissolve and come back in time if it’s drop off.

Fusible links are self-dissolving bonds. After 16 hours in seawater, those bonds disintegrate, the weight bags drop off automatically, and you go back to the surface.

thank you, couldn't find the right part of the interview

Great, in theory. All the operator has to do now is to show the test reports for all of that. Should be easy, right? After all, those functions can be tested in comparatively safe depths, while being tethered to a surface ship.

> There's little other explanation for why contact would be abruptly lost.

You'd think - but past passengers have said that when they dove they lost contact as well.

Mutiple trip passengers said they lost contact every time.

So multiple anecdotes of loss of contact with the same vehicle without an implosion. The jankiness of this operation continues to be discovered bit by bit.

ETA:

https://abcnews.go.com/US/former-titanic-submersible-passeng...

I listened to Reiss's (the passenger cited in that story) account on his podcast [0], and it's somewhat ambiguous. There are periods of spotty communication and long periods of the sub just getting lost. But not comms system/transponder abruptly going out and not being heard from again.

David Pogue seems to concur with this [1]. He saw them lose track of where the sub was located (wrt to the Titanic wreck), but he said the support ship never lost the ability to communicate with the sub.

[0] https://bleav.com/shows/what-am-i-doing-here-with-mike-reiss...

[1] https://twitter.com/Pogue/status/1671524465736335366

In addition, note that despite losing contact while the sub was on its way down, they did not report it missing until it was overdue after the full mission length.

That indicates a certain blase, routine attitude to communication loss.

This is consistent with this video of a trip. Comms were lost, and the pilot even jettisoned some of the ballast in order to resurface. They continued the descent later though.

https://m.youtube.com/watch?v=RAncVNaw5N0

> That's not true, they've successfully reached the Titanic several times over a dozen or so expeditions.

This is more concerning, given that metal fatigue is an understood phenomenon (1).

(1) https://www.faa.gov/lessons_learned/transport_airplane/accid...

It's a carbon fiber hull, for which I think we know alot less about repeated stress events...

> It's a carbon fiber hull

...With titanium hemispheres at each end, so some sort of poorly understood titanium carbon-fibre interface.

I know first hand how hard it is to design carbon fibre preasure bulk heads, for aircraft with a much lower preasure delta (I wrote my first thesis about how to produce something like that). So, on the sirface, titanium makes sense. Using both, carbon fiber and titatium is just, well, not a good idea. Especially since I have the feeling this whole things wasn't properly calculated in the first place.