If we are going to use people to colonise space the best way to achieve this is to design/engineer them.First of all we need little people. Less mass to have to be carted around by your propulsion system. Next we should deal with the big problem of space outside of the magnetosphere, ionising radiation. The tissues which are most easily damaged by this are the ones with rapidly dividing cells. So get rid of hair follicles, get a very slow bone marrow, get rid of the digestive tract (feed will have to be taken intravenously) get rid of gonads (sensitive to radiation and stops our drone humans from creating their own dynasty when they land. The CNS does not make new neurones as an adult therefore our drones would be allowed a brain, larger than ours if we like. The end result will be anaemic and quite weak. But should be relatively long lived and resistant to the effects of radiation. It would also coincidentally resemble descriptions of "greys" in the tabloid media.