3.5km is about correct. Lake Vostok is really deep down below.

there may be ways to go without too much pressure protection if there are no humans to protect. i think they can build the equipment such that is works under high pressure.

I am one of the "anti nuclear folks" (in my case, german greens), because I think it is too dirty and dangerous to be used for terrestrial power production, where there are other possibilities. In space exploration there are none (for the most part), so I think it's inevitable there. They should try not to blow up on launch though…

Another thought. The pressure that must reside under 6 km of ice even on the reduced gravity load of Europa must be intense. The pressure shell required will be heavy, even with the use of ceramics etc. Combine that with the nuclear reactor to produce enough heat to melt the channel for the sub to descend through and you have a honking big mass to throw towards Jupiter.

Not to mention the anti nuclear folks are going to go over the top on this one.

On a positive note, maybe we actually have a use for the Ares V rocket after all.

Jamie

Also, while we're not yet certain that there's a subsurface ocean on Europa, the chances (from what we've observed so far) appear very high.

So they build a robot to go explore an ocean that they dont know if it even exists?
thats smart…