"Fairly easy" seems a little dismissive; if it were even remotely easy, it would've been done earlier and more often, for all sorts of reasons. Neither problem

"Fairly easy" seems a little dismissive; if it were even remotely easy, it would've been done earlier and more often, for all sorts of reasons. Neither problem is at all trivial, and the one the rocket addresses (getting there) is not the same one the construction of a submersible does (staying there). I don't think the two endeavors are really comparable in any useful way; they're both pretty impressive in terms of logistics.