The world's richest person is on the doorstep of trillionaire status. SpaceX CEO Elon Musk owns a stake in his reusable rocket maker that's worth $866.5 billion on paper, according to the company's updated IPO prospectus published on Wednesday. SpaceX said it plans to price its upcoming IPO at $135 a share for a valuation of about $1.77 trillion. For the 54-year old Musk, the SpaceX offering, which is expected next week, comes 16 years after he took Tesla public. Now he owns stock in the