A SpaceX Starship prototype rocket exploded on landing after an otherwise successful high-altitude experimental launch from Boca Chica, Texas, on Tuesday, in a repeat of an accident that destroyed a previous test rocket. The Starship SN9 that blew up on its final descent, like the SN8 before it, was a prototype for the heavy-lift rocket being developed by billionaire entrepreneur Elon Musk’s private space company to carry humans and 100 tons of cargo on future missions to the moon and Mars. The self-guided, 16-story-tall rocket initially soared into the clear South Texas sky from its launch pad on what appeared from NASA-SpaceX livestream coverage to be a flawless liftoff. Reaching the peak of its flight, the spacecraft then hovered momentarily in midair, shut off its engines and executed a planned “belly-flop” maneuver to descend nose-down under aerodynamic control back toward Earth. The trouble appeared to come when the Starship, after …