always been about taking everything you can with you wherever you go. now, this is possible, but it's very expensive. it's very difficult to do. so what we're looking at now is, in the longer term, we want to make exploration sustainable and permanent. oxygen, for example, is something that we need on the moon for propulsion, for rocket fuel and for breathing. we can get that out of ice at the lunar poles and from lunar rocks, which are made of about 40% oxygen. we're also left with metals, and those metals can be used to make equipment, make materials. the moon is also the only place we can go, three days away, to start to understand what it means to live and work away from the earth. so if we want to learn how to use resources locally and in a responsible and clever way to prepare us for going on to mars and elsewhere, the moon is where we have to do it. of course, this won't happen tomorrow. but technological advancement is starting to push forward the possibilities of learning more about the moon, followed by mars and beyond.