Most nations on Earth engage in trade. I'm sure Mars would do so as well. Because of the expense involved, soon the only thing Mars would ship in would be computer components that require a large fab.
There's a difference between "can be self-sustaining" and "is self-sustaining." A successful Mars colony would engage in trade with Earth.
There's a difference between "can be self-sustaining" and "is self-sustaining." A successful Mars colony would engage in trade with Earth.
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