Using a manned Europan submersile as an astronaut test
A guest blogger on The Planetary Society Web site has been describing
his journey as a Japanese candidate for the astronaut corps.
One of their tests involved being part of a manned submarine designed
to explore Europa's hidden liquid water ocean:
http://www.planetary.org/blog/article/00001999/
Some day it will be much more than just a training/thought exercise.