There are dozens of speculative proposals to explore Europa, Enceladus, and possibly other Solar System bodies (including Sedna and other Trans-Neptunians!) that may be endowed with liquid water under a crust of ice (due to tidal heating or radioactive decay). One of them (IIRC) was sending crawling robots to exploit (possibly non-existing) cracks in the ice. Another set of rather fantastic-looking proposals hinges on manned exploration and drilling. There are also ice-melting cryobot ideas floating aroung.
I'm interested in cheaper and preferably reliable ways of getting knowledge about the properties of these oceans up to tests for presence of life in situ, without sample return.
What is the limit of data obtainable from orbital missions? (please state notional or existing instruments and orbits required, including perhaps multi-satellite formations)
How can we get data from inside the oceans? (Can, for instance, penetrators be used - cf. LCROSS?)