#5 is fairly useless AFAIK, because the exact same problem applies to the bottom of the (deep)ocean, and IIRC the ocean is cheaper to get to. Although the pres

#5 is fairly useless AFAIK, because the exact same problem applies to the bottom of the (deep)ocean, and IIRC the ocean is cheaper to get to. Although the pressure problem is inverted, IIRC - space has zero pressure outside, whereas the ocean bottom has crush-depth pressure outside.