One minute before SpaceX's Falcon 9 rocket was supposed to launch for a cargo resupply mission to the International Space Station this morning, SpaceX aborted the mission. The launch would have been its fifth mission to ISS, but its first attempt at landing a rocket on a barge out at sea. But because of an issue with a "thrust vector control actuator," the launch and historic landing have now been delayed. The next attempt will be Friday morning at 5:09AM ET, NASA said, "pending resolution of the issue."

The launch was halted by the flight team because a thrust vector control actuator wasn't functioning correctly. The actuator was central to the landing mission and would have triggered an automatic abort if the team hadn't stepped in to stop the launch. This was the second delay for SpaceX's landing mission. In December, SpaceX delayed a launch prior to the actual attempt because of a problem with routine test-firing of the engine.

SpaceX's launch mission was secondary to its landing mission, in which the company planned to land a 14 story-tall rocket on a barge measuring 300 feet by 100 feet. Doing so represents an important step for spaceflight because being able to conserve a rocket — or parts of one — after a mission would make the whole endeavor a lot cheaper. But SpaceX knew the mission wouldn't be easy. In the past, it has compared the feat to balancing "a rubber broomstick on your hand in the middle of a wind storm."