Watching Apollo 13 and rereading Lost Moon, Jim Lovell's exciting recollection of the events on the crippled spaceship, I began to wonder. Why does NASA maintain the gasses at the triple point? A pressure vessel designed to handle very high vacuum (which H2 and O2 triple points are near complete vacuum) and low temperatures is thicker and more dense then a pressure vessel designed to handle modest amounts of pressure. Why wouldn't they store these gasses at higher pressures, at or near atmospheric pressure?
If you want a few hundred pages of gory detail on gas management, I found an original research report here.
Looking at excerpts from a book on cryogenics, one thing that's pointed out is that the triple point provides a stable pressure inside the container even as energy is added or removed, because the energy just changes some of the material from one state to another. By comparison, a can of LOX needs pressure management because a little heat produces a gas head, and so on.