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Lander aside, the biggest limiting factor is getting astronauts back from Mars! We already know how to get things there, and I think the lander issue is relativ

• Robotbeat 9y ago
  Correct. In my post, I was assuming "lander" would either be a two-stage vehicle like the Apollo lunar lander capable of both landing and later ascending (with or without refueling) or a single-stage vehicle (like SpaceX is developing with ITS/BFS) that is capable of being refueled on the surface for ascending. And yes, fueling up on the surface is a difficult problem to solve. It will involve at least extraction and electrolysis of CO2 from the Mars atmosphere (as NASA is going to demonstrate on the Mars 2020 Rover), but most probably will also include extraction of water, probably by using a robotic machine to dig up regolith (which contains at least 2% absorbed water almost anywhere on the surface of Mars) or buried ice, electrolysis of that water and reaction of the resultant hydrogen with CO2 from the atmosphere to make methane. (And in both cases of electrolysis, you'll be producing sufficient oxygen.) This is, of course, partly why SpaceX is developing a methane-based engine for their next-generation launch vehicle. But you have to develop the lander first otherwise you can't feasibly land enough equipment (using existing techniques limited to just a single ton) to refuel.