There’s a lot of technology required to get humans to Mars. That’s the main takeaway I come away with after talking to NASA’s chief technologist, David Miller. It’s a trite observation, to be sure—but having all the challenges laid out really hammers the point home. “It’s one of those things where there are so many things you can work on,” he told me. “But you have to pick and choose, and you have to choose wisely.” Some of it you likely would never have considered. Take “water walls.” Line your space shuttle with water and hey presto: you both help protect against radiation during the journey and transport a vital resource for your astronauts. “Water with hydrogen content absorbs radiation to some degree,” Miller explained. “Seeing as you need to take water, maybe you could line the walls of your capsule with water. So it’s used for drinking as well as shielding.” I spoke to Miller after he gave a talk with NASA’s chief scientist, Ellen Stofan, at the Royal Institution in London. The pair discussed the US space agency’s plans for human exploration of Mars, and what it’ll take to meet President Obama’s target of a manned mission to the Red Planet’s orbit by the 2030s, followed by a Mars landing. The longer they talked, the more challenges became clear, until the whole idea of sending people into space at all seemed ridiculous. Stofan gave an overview of some of the scientific challenges such a mission presented—from radiation to potentially toxic dust—and Miller added insight into the kinds of tech we’ll need to develop to overcome them. The main steps: “We have to be able to land there, we have to be able to live and work productively, and we also have to be able to return home.” More via Motherboard.