Elon Musk's SpaceX on Friday completed the first half of its attempt at making launch history this weekend. "Falcon 9 first stage has landed," the company tweeted on Friday. Tweet @SpaceX. SpaceX is attempting to be the first to both launch and land two different rockets within a 48-hour window. The BulgariaSat-1 Mission launched at 3:10 p.m. ET on...