By Joe Skipper and Steve Gorman

BOCA CHICA, Texas (Reuters) -SpaceX's next-generation Starship spacecraft exploded minutes after liftoff in an uncrewed test flight from South Texas on Thursday, cutting short a key step in Elon Musk's development of a rocket vessel to eventually take humans to the moon and Mars.

The flight test was the first for Starship mounted atop the company's new Super Heavy rocket, and the first launch ever for that lower-stage booster, which SpaceX has touted as the most powerful launch vehicle on Earth.

Even though the two-stage rocket ship made it less than halfway to the edge of space, climbing to just under 25 miles (40 km), the flight achieved a primary objective of getting the new vehicle off the ground at liftoff despite some of its engines failing.

While SpaceX officials were heartened by the outcome, the mission fell short of reaching several objectives.

The plan was for Starship to soar into space at least 90 some miles (150 km) above Earth before it would re-enter the atmosphere and plunge into the Pacific near Hawaii.

But SpaceX said in a statement afterward that the spacecraft "experienced multiple engines out" during its ascent, then "lost altitude and began to tumble," before the "flight termination system was commanded on both the booster and the ship."

Musk, SpaceX's founder, chief executive and chief engineer, had appeared eager to temper expectations in remarks made Sunday that downplayed the odds of a successful first flight. SpaceX President Gwynne Shotwell told a conference in February that the "the real goal is to not blow up the launch pad."

By that measure, the debut flight of Starship with its booster rocket represented a milestone in SpaceX's ambition of sending astronauts back to the moon and ultimately to Mars, as a major partner in Artemis, NASA's newly inaugurated human spaceflight program.

NASA chief Bill Nelson congratulated SpaceX on Twitter, saying, "every great achievement throughout history has demanded some level of calculated risk, because with great risk comes great reward."