A planned test launch of SpaceX's most powerful rocket scheduled for Monday was postponed due to technical issues, according to the company and its founder, Elon Musk.
Musk tweeted at 1311 GMT that a "pressurant valve" on the SpaceX rocket "appears to be frozen." Minutes later, SpaceX tweeted that the company was "standing down from today's flight test attempt."
The SpaceX "team is working towards next available opportunity," the company added.
"Learned a lot today, now offloading propellant, retrying in a few days..." Musk added.
The flight, scheduled to be launched from a site in Texas, had been expected to last about 90 minutes.
Dubbed the Super Heavy Rocket by SpaceX, the rocket is the most powerful ever built and is intended to eventually carry SpaceX's large Starship spacecraft to the moon and Mars.
The test flight had been due to begin around 7 am on Monday (1200 GMT) and to last about 90 minutes.
The Starship system was designed in such a way that both the spaceship and rocket could be reused after returning to Earth.
Overall, the system is 120 metres high and cab transport well over 100 tons of cargo, more than any other rocket built to date.
US government space agency NASA is hoping to use the Starship system to eventually carry astronauts back to the moon. SpaceX holds ambitions of one day travelling further to Mars.
The rocket is powered by 33 Raptor engines that run on liquid methane and liquid oxygen. The system is designed to allow it to be refuelled in space.
SpaceX sought to temper expectations for the text flight in advance of Monday's launch.
"With a test such as this, success is measured by how much we can learn, which will inform and improve the probability of success in the future," the company said in a statement on Friday.
Musk had earlier tweeted, "Success maybe, excitement guaranteed!"
