SpaceX scrubbed the launch of a relief crew on Wednesday night, delaying the handoff for NASA astronauts who have been awaiting a return trip to Earth.

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.

Astronauts Sunita Williams, who grew up in Needham, and Butch Wilmore have been living on the space station since June after the Boeing Starliner capsule they arrived on experienced issues while docking.