SpaceX’s mega Starship rocket blasted off from Texas on Thursday, the fourth test flight for the spaceship that NASA and Elon Musk are counting on to get humanity to the moon and Mars. The world’s largest and most powerful rocket — almost 400 feet (121 meters) tall — was empty as it soared above the Gulf of Mexico and headed east. The spacecraft on top was aiming for a half-lap around the planet with a splashdown in the Indian Ocean, once it ditched the first-stage booster in the gulf. This time, SpaceX was looking to avoid explosions by controlling the descents. SpaceX came close in March, but lost contact with the spacecraft as it careened out of space and blew up short of its goal. The booster also ruptured in flight, a quarter-mile above the gulf. Last year’s two test flights ended in explosions shortly after blasting off from the southern tip of Texas near the Mexican border. The first one cratered the pad at Boca Chica Beach and hurled debris for thousands of feet (meters).