Takeoff was slated for Wednesday evening from Kennedy Space Center in Florida, but the company called off the launch attempt because of an issue with the launchpad’s ground system. The problem stemmed from a hydraulics system used to control one of two clamps that hold on to the upper portion of the rocket as it sits vertically on the ground pad before launch.

NASA and SpaceX on Wednesday night scrubbed the Falcon 9 launch of a flight intended to retrieve from the International Space Station astronauts Suni Williams and Butch Wilmore, who have spent nine months in orbit.