Malachi Constant said:
How can we create a robotic mechanism that can land on Mars a few month before starship that's capable of building a rudimentary landing pad?
The robot bring along some cement, finds out how to make the Martian dirt into concrete, pulls water out of the atmosphere and slowly but surely 'paves' a basic pad for starship to land on.
Concrete doesn't really work when the ambient temp is around -80*F. You'd need a lot of additives ,blankets, and probably even heaters to start the chemical reactions that actually make concrete and then keep them going until it's cured. You also need the water to maintain its liquid form at -80*F in order to place the concrete.
The atmosphere is incredibly thin and only has trace amounts of water. You'd never get enough for a concrete pad even if you could get the chemistry of the reactions to work.
Assuming you could in fact get the water necessary and land enough additives, insulation blankets, and heaters to start and maintain the reaction, concrete has no tensile strength to speak of. The pad would need to be exceptionally thick to not crack under the weight of a Starship without steel or plastic reinforcement. There are ways that pads and other structures can be formed and structurally sound without steel, but they all require other materials that don't exist on Mars and would need to be brought. Iron is readily available on Mars, but not in any feasibly usable form to make reinforcement there.
And then there's the weight problem. A concrete mixture sans water is going to weigh just under 2 tons per cubic yard. A 100'x100' 6" thick landing pad, which is admittedly probably too thin, would require ~185 cubic yards. So your looking at 300+ tons of concrete. That's several starships worth of cargo, plus the extra starships to refuel those going to Mars. Then you need the robot(s).
Really the best solution would be pouring some kind of epoxy resin over/in the soil to lock it into place and just harden it. You'd probably need to dig down mix it in though. A thin layer wouldn't support anything or last long enough to provide value for what or would take to get the materials there. We have vehicles here on earth that do something similar, tearing up soil and mixing in additives like lime to stabilize it before base or a road is put over it. That said, you're still looking at very, very heavy machinery and a lot of materials.
