I've long felt excited at the prospect that the oceans of Europa might be explored in my lifetime. Now a British engineer, Carl T. F. Ross, a professor at the University of Portsmouth, has proposed a submarine design that might be appropriate:
Ross’s paper weighs the options for constructing a submarine capable of withstanding the undoubtedly high pressure within Europa’s deep oceans. Scientists believe that this moon’s oceans could be up to 100 kilometers deep, more than ten times deeper than Earth’s oceans. Ross proposes a 3 meter long cylindrical sub with an internal diameter of 1 meter. He believes that steel or titanium, while strong enough to withstand the hydrostatic pressure, would be unsuitable as the vessel would have no reserve buoyancy. Therefore, the sub would sink like a rock to the bottom of the ocean. A metal matrix or ceramic composite would offer the best combination of strength and buoyancy.That seems optimistic, but I hope he's right.
Ross concedes that a submarine mission to Europa won’t occur for at least 15-20 years.