SpaceX goes public today at a huge valuation, and this looks like a classic bubble — risky for retail buyers, great for Elon Musk and early insiders.

• SpaceX is going public at a valuation near $1.8 trillion, even though it has never made a profit and lost billions in recent years.
• Retail buyers mostly got tiny allotments, and a first-day price spike is likely to be followed by a drop as early buyers cash out.
• If the shares hold above $140, Musk is expected to become the world's first trillionaire, mostly on his Tesla and SpaceX stakes.
• New index-fund rules mean many people could soon own SpaceX through their 401(k) without choosing to.
• Analysts at Morningstar think it's worth less than half the IPO price, and Musk keeps 82% of voting control regardless.

Outlook: Expect wild first-day swings and likely a slide after the early pop, with the long-term price far below the hype.