I won’t say I think outer space is easier, but the problem space is very different.
I won’t say I think outer space is easier, but the problem space is very different.
As a boat owner, I have had quite a time with salt water issues. Anything with an electrical current going through it exposed to salt and water is subject to serious, rapid corrosion. What you might imagine is "stainless" steel will, in fact, rust (unless correctly passivated and treated). The galvanic scale is not to be trifled with :). I can only imagine it gets exponentially worse the further below the surface you go.
You didn't even mention pressure. Space is only 1 atm off of sea level. 100 meters below the surface is 10 atm more than at sea level ... all sorts of cool stuff you might want to explore is way deeper than that.
Less of a problem for robots than people, but still a problem.