http://m.space.com/19872-skylon-space-plane-human-spaceflight.html I don't have a background in aerospace engineering but I am interested to know the main reasons as to why it is so difficult for single stage vehicle to go all the way to orbit. Is it about the fuel constraints and the weight? the weight of a multistage vehicle keeps going down as the initial stages are detached away, right ? Is that the reason for multistage rockets ? I would like to know all the reasons.