Enlarge / Saturday’s launch attempt of a Falcon 9 rocket was called off just 13 seconds before liftoff. (credit: Trevore Mahlmann)

Another day, another launch attempt for SpaceX. Although the company’s countdown on Saturday toward liftoff of a Falcon 9 rocket from historic Launch Complex 39A proceeded mostly smoothly, SpaceX founder Elon Musk called it off during the last moments. He said he wanted to make sure a slight steering issue with an engine in the rocket’s upper stage was not indicative of a more significant upstream problem.

Today the rocket appears ready to go for a 9:39am ET (14:39pm UK) instantaneous launch time from Kennedy Space Center. The company said it has replaced the parts at issue with the second stage steering issue. That leaves unacceptable weather as the only issue, and according to Launch Weather Officer Mike McAleenan, the primary concern is for cumulus clouds and the possibility of having to fly through precipitation.

If the Falcon 9 rocket launches on Sunday morning, it would mark an important moment for SpaceX. NASA built two main launch pads during the Apollo program, 39A and 39B. The former was used for every Moon landing launch, except for Apollo 10, and most of the space shuttle missions. After the final space shuttle flight in 2011, NASA decided it needed just one of the pads for its future operations. So it leased Launch Complex 39A to SpaceX.