Hunter Williams used to be an English teacher. Then, three years into that job, he started reading the book The Moon Is a Harsh Mistress. The 1966 novel by Robert Heinlein takes place in the 2070s, on the moon, which, in this future, hosts a subterranean penal colony. Like all good sci-fi, the plot hinges on a rebellion and a computer that gains self-awareness. But more important to Williams were two basic fictional facts: First, people lived on the moon. Second, they mined the moon.