SpaceX had its initial public offering last week. Now Elon Musk is a trillionaire on paper. But what is SpaceX? On one level, of course, SpaceX is a company that builds rockets and spacecraft and launches them into space. (Occasionally the rockets explode.) It is also the company that birthed Starlink, a satellite-internet business that generated more than $11 billion in revenue last year. But the company can be defined in many ways. SpaceX is a financial instrument for Musk. Before the IPO,