Everyone wants a piece of SpaceX. But how can you invest in SpaceX stock?Last year, Amazon.com (NASDAQ: AMZN) "competitive intelligence tools" subsidiary Alexa (yes, Alexa has a side job) reported on how SpaceX's website has become one of the most popular corporate websites among privately held companies. As measured by "unique visitors," more people are looking into SpaceX than any other "unicorn" stock on the planet.It's no mystery why.