SpaceX stock fell back down below its IPO price of $135 a share on Tuesday. Earlier this week, Elon Musk's SpaceX (SPCX) surpassed its IPO price for the first time since mid-July. The stock fell 3.9% to 133.29 on Tuesday, according to MarketSurge. Tuesday's retreat snaps a three-day winning streak in which SpaceX gained just under 30%. All three days…