It makes little sense to send people to Mars to build a city, as people need a level of infrastructure that makes living there impractical until you build the infrastructure needed to survive.
It makes a lot more sense to send machines to build the environment and send people later.
What if robots could mine raw materials, build the factories to process the raw material, build the infrastructure to build more robots that could then build everything needed to sustain life.
There is no reason why this cannot be done!
Phase 1 – Robots investigate available raw materials (survey)
Phase 2 – Robots mine raw materials (mine)
Phase 3 – Robots use the initial raw material to build refineries to produce building materials and factories (Build)
Phase 4 – Robots build more robots out of refined material (replicate)
Phase 5 – Robots now build everything needed to sustain life (buildings, machines, infrastructure) (Implement)
Phase 6 – People arrive (Immigrate)
How long would it take? 50 years, 500 years? Probably somewhere in between.
I believe phases 1 and 2 are almost practical today. While phase 3 is partially possible today.
It could be started on Earth right now. Build the technology to build cities from nothing, anywhere on the planet, and potentially beyond.
A few square miles of barren land, a lot of smart minds, enough investment to make it happen.
This is the project that is needed!