Elon Musk, no stranger to outlandish pledges, just teased around-the-world flights aboard one of his rockets. The chief executive of Tesla Inc. TSLA, +1.63%and Space Exploration Technologies Corp. was tweeting about SpaceX’s latest mission when he veered toward the stuff of sci-fi. Earth-to-earth rocket flights could carry about 1,000 people. Alas, all seats would be coach, and there would be no toilets, but on the plus side most trips would take only 15 to 20 minutes, Musk tweeted. It would be “unwise” to let passengers move about during the flights, likening the experience to Disney’sfamed Space Mountain roller-coaster ride: