Key PointsElon Musk's SpaceX is gearing up for its initial public offering (IPO), which could value the space exploration company at as much as $2 trillion.It may be hard for retail investors to participate in the offering prior to its listing, but there are three widely available stocks that give indirect exposure.10 stocks we like better than EchoStar › After years of anticipation, privately held SpaceX finally has plans to go public. The Elon…