NEW YORK, April 29 : In the days after the PayPal IPO in 2002, Elon Musk and company executives gathered at a Las Vegas casino to celebrate. But while others socialized by the pool, Musk was hunched over an old Soviet rocket manual and already planning his next venture: SpaceX. “He’d come off what was an unequivocally big win, he was one of the largest shareholders, and yet he was focused on this next thing,” Kevin Hartz, an early PayPal investor who was at the party, told Reuters. “Now it’s a