NEW YORK, June 7 -- The question hanging over SpaceX's June 12 market debut is not whether Elon Musk can fill an order book. He can. It is whether the same retail investors who turned Tesla into the most widely held stock on Robinhood are willing to split their capital between two Musk companies simultaneously - and what happens to both stocks if they aren't.

That tension sits at the center of an IPO unlike any Wall Street has processed. SpaceX is targeting a $1.75 trillion valuation at $135 per share, a raise of roughly $75 billion that would surpass Saudi Aramco's 2019 debut as the largest public offering in history. The roadshow launched the week of June 8, with 125 analysts from 21 underwriting banks meeting the company before instit...