09:50am update: Despite mostly cloudy skies, SpaceX successfully launched from Kennedy Space Center's 39A pad on Sunday. After the first stage of the Falcon 9 rocket delivered its payload—a Dragon spacecraft—into low-Earth orbit, the booster flew back to Earth and stuck its landing. SpaceX is now three-for-three in attempts to land its first stage boosters at Landing Zone 1 on the Florida coast.

Check back later today as Ars will have some exclusive photos of the historic first private liftoff from Launch Complex 39A.

Original post: 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, 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.

Now, after modifications and upgrades, the historic pad is finally ready for its second life. The Falcon 9 rocket will boost a Dragon spacecraft carrying about 2.5 tons of food, water, and scientific experiments to the International Space Station. About 10 minutes after launch, the first stage of the rocket will attempt to land back at Landing Zone 1, near the launch pad. So far, SpaceX is two for two with land-based returns of its rocket. The webcast will begin at about 9:20am ET: