SpaceX scrubs test flight of giant Starship rocket

SpaceX scrubbed the launch of its powerful Starship rocket -- which is expected to eventually carry passengers to the moon and Mars -- that was set for Monday morning.

The uncrewed launch of the world's largest rocket would have marked the first flight test of a "fully integrated" Starship spacecraft and the so-called Super Heavy rocket, SpaceX said. SpaceX CEO Elon Musk said on Twitter just before the launch that a "pressurant valve appears to be frozen," ending the possibility of any launch Monday.

SpaceX said the attempted launch would now be turned into a wet dress rehearsal, meaning it simulates every stage of rocket launch but without liftoff actually occurring.

The 150-minute test window opened at 7 a.m. CT Monday, SpaceX said, and the company was aiming for a 8:20 a.m. CT launch. A live webcast of the flight test began 45 minutes before expected liftoff and the countdown clock was taken down to the 10-second mark before stopping.

During the webcast, the team said it would need at least 48 hours to reset the rocket and figure out why the pressurization issue occurred before attempting to launch Starship again.

"Learned a lot today, now offloading propellant, retrying in a few days," Musk tweeted after the launch was scrubbed.

The timing comes after the Federal Aviation Administration on Friday approved SpaceX's launch of the nearly 400-foot-tall rocket from a remote site on the southernmost tip of Texas near Boca Chica Beach.

"Success maybe, excitement guaranteed!" Musk tweeted Friday night.

During a Twitter "Spaces" event for subscribers Sunday evening, Musk warned to set expectations "low."

Following blastoff, the first stage of the Super Heavy rocket is expected to splash down about 20 miles off the coast of Boca Chica while the Starship vehicle orbits around the globe before splashing down off the coast of Hawaii.

For this first flight test, SpaceX said it will not attempt a vertical landing of Starship or a catch of the booster.

SpaceX said this flight test will "inform and improve the probability of success in the future as SpaceX rapidly advances development of Starship," which is designed to carry up to 100 people on long-duration, interplanetary flights.

NASA has already announced plans to use a Starship to put astronauts on the lunar surface in 2025.

ABC News' Gina Sunseri contributed to this report.