NASA has, for the moment, killed funding for research leading to an underwater
probe for Europa's suspected saltwater ocean. But it's possible that this is a
good thing. SPACE.com proposes that U.S. Navy-funded research into underwater
gliders could offer a superior means of probing Europa, exploring Venus, and
even diving into the methane/ethane seas of Titan. NASA wanted a big battery
and propeller machine under the ice of Europa, but that might break down, stir
up water that should left undisturbed, and leak lubricants into a prestine
research environment. The navy wants gliders with internal actuators because
they have no flaps or propellers, no lubricant, and one already exists that
could "fly" under the Pacific from Seattle to Tokyo on a penlight battery!
Another model uses no batteries for locomotion at all, but instead taps heat
gradients.
http://space.com/businesstechnology/technology/sea_glider_020410-1.html
