A boater passes SpaceX’s Starship, the world’s biggest and most powerful rocket Monday as it prepares to lift off from Starbase in Boca Chica, Texas. Eric Gay/Associated Press

SOUTH PADRE ISLAND, Texas — SpaceX called off its first launch attempt of its giant rocket Monday after a problem cropped up during fueling.

Elon Musk’s company had planned to fly the nearly 400-foot Starship rocket from the southern tip of Texas, near the Mexican border.

The countdown was halted at the 40-second mark because of a stuck valve in the first-stage booster. Launch controllers couldn’t fix the frozen valve in time, and canceled the attempt. The countdown continued, and fueling was completed, as a dress rehearsal.

No people or satellites were aboard. There won’t be another try until at least Wednesday.

“Learned a lot today,” Musk tweeted after the flight was postponed.

The company plans to use Starship to send people and cargo to the moon and, ultimately, Mars.

On the eve of the launch attempt, cars, campers, RVs and even bicycles and horses jammed the only road leading to the launch pad, where the stainless steel rocket towered above the flat scrubland and prairie. Enthusiasts posed in front of the giant letters that spelled out Starbase at the entrance of the SpaceX complex, and in front of the rocket two miles farther down the road, which ended at the gulf.

On Monday, spectators were barred from the area, and instead packed a beach about six miles away on South Padre Island.

Ernesto and Maria Carreon drove two hours from Mission, Texas, with their two daughters, 5 and 7, to watch.

“I got sad. They got sad,” when the launch attempt was canceled, Maria Carreon said.

They can’t return for the next try but planned to have fun on the beach Monday.

Michelle Vancampenhout, on vacation from Green Bay, Wisconsin, said she’ll be back.

“It’s a once-in-a-lifetime experience to see it,” she said.