In 2015, Alphabet (GOOG +0.19%) (GOOGL +0.36%) invested about $1 billion in Space Exploration Technologies (SPCX -4.72%), better known as SpaceX. As of the end of the second quarter, its stake was worth $94.1 billion, according to Alphabet’s second-quarter earnings release. A lot has changed at the rocket company over the decade-plus since Alphabet’s initial…