This is CNBC's live coverage of the SpaceX IPO, as Elon Musk's artificial intelligence and space company starts trading for the first time. SpaceX begins trading Friday under the ticker SPCX after the biggest initial public offering ever. Elon Musk's reusable rocket company said in a filing with the Securities and Exchange Commission late Thursday that it's raising $75 billion, selling 555.6 million shares for $135 a piece. The deal values SpaceX at $1.77 trillion, making it the seventh most-