Well, you need to be able to change the weight of the capsule somehow, otherwise you'd be stuck bobbing at the surface. (Or at the seabed). The puzzling bit, f

Well, you need to be able to change the weight of the capsule somehow, otherwise you'd be stuck bobbing at the surface. (Or at the seabed). The puzzling bit, from what I have gathered, is that the ballast is not fail safe.