Wouldn't the Moon, so much nearer than Mars, be a better first step? Actually, no โ€“ it's just too different. It's better to test hardware and train people in analogs on Earth, such as the geologically similar high-altitude desert in Utah or the cold and dry Canadian Arctic desert. Why the European Space Agency has declared the Moon a stepping-stone to Mars is beyond me, as doing so increases the cost of a Mars programme hugely.