Does a submersible like this only drop ballast weight in an emergency, or every time they’re ready to go home? I know submarines tend to use diving planes and pneumatic ballast tanks (flood with water, or inject air to push water out), but I don’t know if that’s an option down at 400 atm.
I heard an interview this afternoon on NPR with David Pogue (the bbc guy who filmed a ride). He said there are 7 different ways of surfacing, including several that do not require electricity and don't even require consciousness. For example, some of the ballast is attached by mounts that dissolve after a certain number of hours in water (presumably less than 96).
