By Joe Skipper, Joey Roulette and Steve Gorman

BOCA CHICA, Texas SpaceX's next-generation spacecraft Starship, developed to carry astronauts to the moon and beyond, was set for blastoff on Saturday for a repeat test launch from south Texas, seven months after its first attempt to reach space ended with an explosion.

The uncrewed launch was scheduled to take place during a 20-minute window beginning at 7 a.m. CST (1300 GMT) at SpaceX's Starbase site on the Gulf of Mexico near Boca Chica. Starship is mounted atop its towering Super Heavy rocket booster in what will be the second attempted flight of both vehicles together.

The mission's objective is to get Starship off the ground in Texas and into space just shy of reaching orbit, then plunge through Earth's atmosphere for a splashdown off Hawaii's coast. The launch had been scheduled for Friday but was pushed back by a day for a last-minute swap of flight-control hardware.

A successful test flight would mark a key step toward achieving SpaceX's ambition of producing a large, multi-purpose, spacecraft capable of sending people and cargo back to the moon later this decade for NASA, and ultimately to Mars.

Elon Musk - SpaceX's founder, chief executive and chief engineer - also sees Starship as eventually replacing the company's workhorse Falcon 9 rocket as the centerpiece of its launch business that already lofts most of the world's satellites and other commercial payloads into space.

NASA, SpaceX's primary customer, has a considerable stake in the success of Starship, which the U.S. space agency is counting on to play a central role in its human spaceflight program, Artemis, successor to the Apollo missions of more than a half century ago that put astronauts on the moon for the first time.

Starship's towering first-stage booster, propelled by 33 Raptor engines, puts the rocket system's full height at some 400 feet (122 meters) and produces thrust twice as powerful as the Saturn V rocket that sent the Apollo astronauts to the moon.

SpaceX is aiming to at least exceed Starship-Super Heavy's performance during its April 20 test flight, when the two-stage spacecraft blew itself to bits less than four minutes into a planned 90-minute flight.

That flight went awry from the start. SpaceX has acknowledged that some of the Super Heavy's 33 Raptor engines malfunctioned on ascent, and that the lower-stage booster rocket failed to separate as designed from the upper-stage Starship before the flight was terminated.

RISK TOLERANCE

The company's engineering culture, considered more risk-tolerant than many of the aerospace industry's more established players, is built on a flight-testing strategy that pushes spacecraft to the point of failure, then fine-tunes improvements through frequent repetition.

A failure at any point in the test flight would be a major concern for NASA, which is counting on SpaceX's rapid rocket development ethos to swiftly get humans to the moon in the U.S. competition with China's lunar ambitions.

Judging the success or failure of the outcome may be less than clear-cut, depending on how far the spacecraft gets this time. NASA Administrator Bill Nelson, who has made the China rivalry a key need for speed, compared Starship's test campaign with the success of SpaceX's past rocket development efforts.

"How did they develop the Falcon 9? They went through many tests, sometimes it blew up," Nelson told Reuters on Tuesday. "They'd find out what went wrong, they'd correct it then go back."

The combined spacecraft in April reached a peak altitude of roughly 25 miles (40 km), only about halfway to space at its target altitude of 90 miles (150 km), before bursting into flames.

Musk has said that an internal fire during Starship's ascent damaged its engines and computers, causing it to stray off course, and that an automatic-destruct command was activated some 40 seconds later than it should have to blow up the rocket.

The launch pad itself was shattered by the force of the blastoff, which also sparked a 3.5-acre (1.4-hectare) brush fire. No one was injured. SpaceX has since reinforced the launch pad with a massive water-cooled steel plate, one of dozens of corrective actions that the U.S. Federal Aviation Administration required before granting a launch license on Wednesday for the second test flight.

(Reporting by Joey Roulette in New York, Steve Gorman in Los Angeles and Joe Skipper in Boca Chica, Texas; Editing by Will Dunham)