NASA engineers are running checks to solve the mystery of why the Falcon 9's engine failed to perform a routine maneuver to lower the rocket's altitude.

SpaceX’s Falcon 9 rocket is grounded again after the vehicle’s second stage did not come down in the expected area of the ocean, following an otherwise successful mission that delivered a Dragon capsule and its crew to orbit. “We will resume launching once we better understand root cause,” the company said in a statement posted to X .

The team of the Dragon Crew-9 boarded the International Space Station after a successful docking Sunday evening, floating through a vestibule joining the two spacecraft .