It's the 21st-century and everything about the space industry is changing. Rather than despair over the end of American manned missions and a moribund commercial launch market, private sector companies are now changing the way humanity accesses orbit. Upstarts including Elon Musk's SpaceX and Jeff Bezos's Blue Origin are building a dizzying array of new spacecraft and rockets, not just for government use, but for any paying customer. At the heart...