SpaceX, the California-based space company founded by Elon Musk, has delayed the first uncrewed test flight of its powerful new Starship rocket due to a pressurization issue in the lower-stage rocket booster. The rocketship, standing at 394 feet (120 m) tall, was set to blast-off from the SpaceX facility at Boca Chica, Texas, during a two-hour launch window that began at 8 a.m. EDT (1200 GMT) on Monday. However, the launch attempt was called off at the last minute, and the mission has been postponed for at least 48 hours.

The Starship rocket is a two-stage vehicle designed for reusable spaceflight. The lower-stage Super Heavy booster rocket and the upper-stage Starship cruise vessel are both reusable components that can fly back to Earth for soft landings, a maneuver that has become routine for SpaceX's smaller Falcon 9 rocket. However, neither stage would be recovered for the expendable first test flight to space, which is expected to last no more than 90 minutes.

Musk, the company's billionaire founder and chief executive, told a private Twitter audience on Sunday night that the mission stood a better chance of being scrubbed than proceeding to launch on Monday.

The successful debut flight of the Starship rocket would be a significant milestone for SpaceX's ambition to send humans back to the moon and ultimately to Mars, initially as part of NASA's newly inaugurated human spaceflight program, Artemis. The Starship system, if successful, would also become the most powerful launch vehicle on Earth.

The prototypes of the Starship cruise vessel have made five sub-space flights up to 6 miles (10 km) above Earth in recent years, but the Super Heavy booster has never left the ground. In February, SpaceX test-fired the booster, igniting 31 of its 33 Raptor engines for roughly 10 seconds with the rocket bolted in place vertically atop a platform.

The Federal Aviation Administration granted a license for the first test flight of the fully stacked rocket system just last Friday, clearing the final regulatory hurdle for the long-awaited launch. If all goes as planned for the next launch bid, all 33 Raptor engines will ignite simultaneously to lift the Starship on a flight that nearly completes a full orbit of the Earth before it re-enters the atmosphere and free-falls into the Pacific at supersonic speed about 60 miles (97 km) off the coast of the northern Hawaiian islands.