The world's most powerful rocket will not be launched into space Monday.
SpaceX scrubbed Starship's launch just moments before takeoff.
Elon Musk, founder and CEO of SpaceX, warned prior to the anticipated launch that there could be a delay.
"A pressurant valve appears to be frozen, so unless it starts operating soon, no launch today," he tweeted.
It's unclear when exactly SpaceX will attempt to try the launch again. Musk said they will try again in "a few days."
NASA's Orion capsule buzzes moon, last big step before lunar orbit
NASA managers said they were delighted with the progress of the mission.
The nearly 400-foot-tall rocket, which will be launching from Texas' Gulf Coast, will not have any crew members or cargo this time around. According to The Associated Press, the first flight will last about 1 1/2 hours.
Starship is billed as a "fully reusable transportation system." The hope is for it to eventually propel humans to the moon and even Mars.
"Starship will be able to carry up to 100 people on long-duration interplanetary flights," SpaceX says.
NASA names astronauts for Artemis II moon mission
The four-member crew of NASA's Artemis II mission, which will attempt to fly around the moon, includes three men and one woman.
