SpaceX is set to launch the first test flight for its redesigned Super Heavy megarocket, the largest rocket ever built, from its new Texas launch pad.

SpaceX got within a half-minute of launching its newest and biggest Starship on a test flight Thursday evening before a cascade of problems halted the countdown.

“For those who think this is simply another repeat test flight, the engineering changes under the rocket ‘hood’ are substantial,” Joseph Gonzalez, an associate professor of practice in aerospace engin...