I know people who work at SpaceX. They recruit pretty heavily from CMU (where I am now). From what I have heard, this is why they get things done so quickly: 1) Elon Musk knows about every detail of the rocket's design. 2) They make almost all the parts in house (literally in the same factory). 3) The work ethic/culture at SpaceX is very high. If something needs to get done, Elon will make sure it gets done fast.
They somehow maintain a high rate of progress despite how huge the undertaking is.
