NASA Is Already Studying What Sort of Person Is Best Suited For Mars (blastingnews.com)
MarkWhittington writes: The first crew to set forth to Mars are likely in Middle School or High School, but NASA is already delving into what criteria it should use to select the interplanetary explorers. That they should be physically fit and experts in their fields are a given. But the space agency is keen that the people who will set forth to Mars in 20 years or so should be of a particular psychological type. NASA has granted Johns Hopkins money to conduct a study into the problem.
You have to get out of the submarine first before you get all that fresh air. You can't just open the door a few hundred feet below the surface.
And even if you get to the surface without suffering from the bends or drowning, you're now facing water temperatures of what -- 70F if you're lucky, and if you're not, much less than that. The same hypothermia that will kill you in space will kill you nearly as fast in the water.