Key PointsSpaceX says it has a $28.5 trillion total addressable market.China's GDP, the second largest in the world, is only $20.8 trillion.10 stocks we like better than Space Exploration Technologies › Space Exploration Technologies (NASDAQ: SPCX) CEO Elon Musk likes to think in trillions. For the world's first trillionaire investor, that probably makes sense. For the rest of us, however, it's hard to imagine what a trillion really is. Mathemat…