Yes, I think we definitely have a gigantic misunderstanding of cable here. Mine is based in reality, while yours seems to be very unrealistic. How in the world is a fiber optic cable going to do what needs to be done? Where is the power coming from to heat the probe via a fiber optic cable? Even a fiber optic cable at a length of 25km is a very large spool. If you want the probe to hold the spool and unwind as it goes, it must be at least the size of the spool of cable. If you think this would work with an unsheathed piece of bare fiber cable, then your just not even trying to be serious.
I see another misunderstanding then. With this method the actual probe would use nuclear material to melt its way through the ice. In addition, the heat of the nuclear probe on one side and the ice on another (or melting ice) would make for the ideal conditions of a peltier (or just use a traditional RTG) device to power onboard sensors and electronics. The fiber optic cable is only for communication.
Simple reactors can be designed to be turned up and down according to need. A 300w RTG is more than enough to run all the necessary electronics. The ice-melting 30,000w+ heater can be a second rector that is spooled up only when ice needs melting.
we're attempting to search for life and the thing you want to do is use radioactive heaters? we deliberately crashed a satellite into the planet to avoid having it potentially contaminate the moons we are curious about, and yet you're thinking they'd just irradiate everything like this? it's really just not logical
In the outer solar system, under miles of ice, in total darkness and cold .. it is nuclear or nothing. Short of antimatter batteries, there is no other source of power that would be even theoretically suitable.
The concern is more spreading Earth life. NASA's Planetary Protection team (which is a delightful job title) is largely concerned with sterilizing stuff we send out so any discovery of microbes on Mars doesn't turn out to be hitchhikers.
Even a fully fleged nuclear reactor isn't gonna do much damage to Europa and potential life. Swimming in a nuclear reactor's fuel pool is quite safe; water's some of the best shielding we have. https://what-if.xkcd.com/29/
