SpaceX's post-IPO mega-rally has hit its first slowdown. Shares in Elon Musk's rocket company, which raised a record $85 billion when it went public last week, had dropped nearly 5% on market close on Wednesday — its first down day. Shares were flat in premarket trading early Thursday. The drop ended a monster share price rally that had seen SpaceX's market cap soar to nearly $3 trillion in its first days of trading, eclipsing Amazon as the world's fifth most valuable company and cementing Musk'