If the colonization strategy is the Moon then Mars, I expect humanity would have the technology needed to colonize Mars easily while terraforming occurs.
The problem with an O’Neil Cylinder is bringing up enough processed material to build one.
The problem with an O’Neil Cylinder is bringing up enough processed material to build one.
One possible solution is a moon base. The moon is full of titanium and iron.
And then you could launch the stuff out of a weaker gravity well with no air resistance.