Tom, I wasn't sure why having the wire freeze in the ice following the probe's descent would be a problem? Unless there were shear effects that would damage it, wouldn't freezing in place make it more stable? The wire would have to unreel from the probe itself, rather than from the surface. How big would the reel have to be? Would booster amps be needed? I'm thinking a fiber optic link...

In any case, this would be a fascinating probe. I wouldn't think the power required to melt though that much ice would be too difficult, though of course a nuclear source would be essential. Hmm, 20 km channel 20 cm in diameter, about 6 x 10^8 cm^3, raising it 100 degrees C (as a rough estimate) requires 6 x 10^10 calories of heat... about the energy in 100,000 Big Macs (given that 1 food calorie = 1000 heat calories)

Aw heck, of course someone has done all the calculations... an interesting site about RTGs on Europa.