SpaceX scrubs test flight of giant Starship rocket due to technical difficulties, CEO Elon Musk says

TEXAS -- 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.

The 150-minute test window opened at 7 a.m. CT Monday, SpaceX said and was aimed for 8:20 a.m. CT launch. A live webcast of the flight test began 45 minutes before expected liftoff.

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 was expected to splash down about 20 miles off the coast of Boca Chica while the Starship vehicle orbited around the globe before splashing down off the coast of Hawaii.

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

SpaceX said this flight test would "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.