SpaceX on Wednesday disclosed its filing for an initial public offering, ahead of an expected stock market debut next month. Why it matters: This is expected to be the largest IPO ever, and could make Elon Musk the world's first trillionaire. Catch up quick: Musk launched SpaceX in 2002 with the goal of one day colonizing Mars. Since then, it has become the world's most successful commercial space company by far and inspired rival efforts by billionaires like Jeff Bezos and Richard Branson. It