Video: The launch of Orion

Fueled segments of the solid rocket boosters that will lift off on the first flight of NASA’s Space Launch System have arrived at the Kennedy Space Center in Florida, but officials will hold off on stacking the boosters until the SLS core stage completes a crucial test-firing later this year.

Kathy Lueders, NASA’s newly appointed head of human spaceflight operations, said Thursday that without a crystal ball, she could not give a yes-or-no answer when asked whether she believes NASA can put astronauts back on the moon by the end of 2024 as called for by the Trump administration.

The four RS-25 engines at the bottom of NASA’s first Space Launch System core stage shut down about a minute into a ground test-firing Saturday that was supposed to last more than eight minutes.