South Padre Island, Texas CNN — 

SpaceX is once again gearing up for the inaugural test flight of Starship, the most powerful rocket ever created and the vehicle that could one day return astronauts to the moon or — perhaps — propel the first trip to Mars.

The rocket could lift off as soon as Thursday, during an hour-long launch window that opens at 8:28 a.m. CT (9:28 a.m. ET). The vehicle is already in position at SpaceX’s privately owned spaceport on the southern tip of Texas.

SpaceX will livestream the launch on its website beginning about 45 minutes prior to liftoff.

The effort will mark the second launch attempt for Starship. The first, on Monday, came to a halt after a problem with a valve created pressurization issues. Engineers opted from there to treat the remainder of launch attempt as a “wet dress rehearsal,” or a practice run that takes teams through all the steps for launch — except liftoff.

The vehicle consists of two parts: The Super Heavy rocket booster, a 230-foot-tall (69-meter-tall) cylinder that houses 33 engines and is expected to send an explosive sound booming across the nearby coastal landscape as it fires to life. The Starship spacecraft, which stands at 164 feet (50 meters) tall, rides atop the rocket.

The Starship rocket sits on the SpaceX Starbase in Boca Chica, Texas, on April 15, 2023./SpaceX

The booster is expected to ignite its engines and vault the spacecraft out over the Gulf of Mexico as it heads toward space.

About two and a half minutes after takeoff, the Super Heavy rocket booster is expected to expend most of its fuel, separate from the Starship spacecraft, and fall into the ocean. The spacecraft will use its own engines, which will burn for more than six minutes, to accelerate to almost orbital speeds — or roughly 17,000 miles per hour.

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Starship will then complete nearly one full lap of the planet, reentering Earth’s atmosphere near Hawaii. It’s expected to splash down in the Pacific Ocean about an hour and a half after liftoff.

About this launch attempt

SpaceX CEO Elon Musk — who has smoked weed on a podcast and previously entered a battle with federal regulators over a cannabis joke — has long had a penchant for embracing the numerical reference to marijuana.

Last week, he even suggested that SpaceX’s first launch attempt on Monday might be delayed so that the company could target a 4/20 liftoff.

Rumors swirling on Tuesday questioned whether SpaceX could hit that target. At one point, the Federal Aviation Administration even took down an air traffic warning for Thursday, sparking speculation that the favored launch date was off the table. It was ultimately reinstated.

Musk has sought to temper expectations for this test launch, saying, “success is not what should be expected …That would be insane.”

Development of Starship has been based at the SpaceX Texas spaceport, about 40 minutes outside Brownsville, on the US-Mexico border.

Testing began years ago with brief “hop tests” of early spacecraft prototypes. The company started with short flights that lifted a few dozen feet off the ground before progressing to high-altitude flights, most of which resulted in dramatic explosions as the company attempted to land the prototypes upright.

One suborbital flight test in May 2021, however, ended in success.

Starship’s ultimate success or failure is immensely consequential. Not only is it crucial to SpaceX’s future as a company — it also underpins the United States government’s ambitions for human exploration of space.

But it’s not all riding on this inaugural test flight. SpaceX has long established its willingness to embrace mishaps, mistakes and explosions in the name of refining the design of its spacecraft.

In the lead-up to the first launch of the company’s Falcon Heavy rocket, which held the title of most powerful rocket before NASA’s Space Launch System took flight last year, Musk foresaw only a 50-50 chance of success.

“People (came) from all around the world to see what will either be a great rocket launch or the best fireworks display they’ve ever seen,” Musk told CNN at the time.

The inaugural Falcon Heavy launch in 2018 was ultimately successful.

It’s common for first-time launches to be delayed as engineers hash out issues that might not have become apparent during prior testing.

NASA’s SLS rocket, for example, underwent four tries to complete a wet dress rehearsal and two launch attempts before the vehicle finally took off in November 2022.