SpaceX has indicated it won’t launch a pair of space tourists to loop around the moon this year as previously announced, the latest sign that technical and production challenges are disrupting founder Elon Musk’s plans for human exploration of the solar system.

A new timetable for the flight—now postponed until at least mid-2019 and likely longer—hasn’t been released by Space Exploration Technologies Corp., the formal name of the closely held company.

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