Successful Launch of SpaceX Falcon 9 Rocket from Historic Launch Pad 39A at Kennedy Space Center

Update 2/19: Sunday a Falcon 9 rocket took off carrying supplies to the ISS. The historic launch marked the first time that a private company lifted off from historic launchpad 39A.

SpaceX delayed its launch of a space station supply mission moments before liftoff Saturday morning. Publicly, the company said there was a possible problem with the second stage of its Dragon rocket. But viewers at the launch site said there was a drone or other UFO near the site.

A UFO was clearly seen in video of the Company's abortive launch in September, which ended in the rocket exploding on the launch pad during refueling.

A hold was called about 13 seconds before the launch. John Federspiel, a lead mechanical design engineer, said on the company's launch webcast that the call was made "out of an abundance of caution" so the company could look into an issue with the "thrust vector control system" on the rocket's second stage.

SpaceX said in a tweet shortly afterward that it was "standing down to take a closer look at positioning of the second stage engine nozzle." The company said it would try to launch again Sunday morning at 6:38 a.m. Pacific time from Launch Complex 39A at the Kennedy Space Center at Cape Canaveral, Fla.

Elon Musk gave some more detail in another tweet. "All systems go, except the movement trace of an upper stage engine steering hydraulic piston was slightly odd. Standing down to investigate," he wrote.

"If this is the only issue, flight would be fine, but need to make sure that it isn't symptomatic of a more significant upstream root cause," Musk tweeted later.

Saturday's issue was not "obviously related" to the "very tiny" helium leak he had tweeted about on Friday. But, he said on Twitter, it was "also not out of the question."

Musk said the possible problem was "99% likely to be fine," but that "1% chance isn't worth rolling the dice." "Better to wait a day," he tweeted.

This will be SpaceX's second launch since one of its Falcon 9 rockets exploded on a Florida launch pad in September.

SpaceX, based in Hawthorne, is set to launch almost 5,500 pounds of science experiments, supplies and research equipment for NASA to the International Space Station.

This will be the first launch from Pad 39A since the last space shuttle mission in 2011. The historic launch pad played a role in both the Apollo and space shuttle programs.

After launch, SpaceX will attempt to land its first-stage rocket booster on land. The Dragon capsule will deploy from the second stage about 10 minutes after launch and is expected to reach the space station two days later.

Last month, SpaceX launched 10 satellites from Vandenberg Air Force Base in California for satellite operator Iridium Communications Inc. The company landed that first-stage rocket on a floating platform in the Pacific Ocean.