When the heavens went on sale, by Ashly Vance, is pretty good. It details the early days of the space start-ups other than spaceX
The Founders: The Story of Paypal and the Entrepreneurs Who Shaped Silicon Valley is also pretty good, describes the crazy days of early paypal.
Someone already mentioned Liftoff by Erig Berger. Starting a private space company is probably as hard as things get, and it describes the early days pretty well