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SpaceX’s Falcon 9 rocket rises from Launch Complex 39A. (NASA via YouTube)

SpaceX sent a rocket rising from NASA’s historic Launch Complex 39A today for the first time since the space shuttle fleet retired, marking a new chapter for a pad that served as the springboard for Apollo moon missions.

The Falcon 9 rocket sent a robotic Dragon capsule toward the International Space Station with almost 5,500 pounds of supplies and experiments, under the terms of SpaceX’s multimillion-dollar contract with NASA.

As a bonus, the rocket’s first-stage booster flew itself back to a perfect touchdown at SpaceX’s Landing Zone 1, not far from the Kennedy Space Center launch site in Florida. That’s part of SpaceX’s plan for reusing hardware and driving down the cost of space launches even further.

Today’s launch marked the first-ever commercial mission to take off from Pad 39, where most of the Apollo missions began in the late 1960s and early 1970s. Lots of other rockets have lifted off from pads at nearby Cape Canaveral Air Force Station since the last shuttle mission in 2011, but not from the space center itself.

This was the second attempt to get the historic mission off the ground.

Saturday’s countdown got to the T-minus-13 seconds before it was called off. The launch team was trying to resolve a concern about the thrust vector control system for the Falcon 9’s second-stage rocket engine, and in the end, SpaceX went with a one-day postponement to give the team more time.

In a series of tweets, SpaceX CEO Elon Musk said nagging worries about the control system led him to postpone Saturday’s launch even though computers were giving the go-ahead.

“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 wrote. He said it wasn’t worth “rolling the dice” on Saturday.

The issue was resolved overnight, and no further worries arose today. Musk’s tweets were far more upbeat:

As the Falcon 9’s first stage slowed itself down from supersonic speeds for its touchdown at Landing Zone 1, sonic booms that could be heard reverberating along the Florida coast.

Meanwhile, the Dragon continued onward and upward, powered by the rocket’s second stage. Spacecraft separation was successful, putting the Dragon on course for a rendezvous with the space station on Wednesday. Astronauts will use the station’s robotic arm to pull the Dragon in for its berthing.

Most of the Dragon’s cargo consists of scientific experiments, including the SAGE III apparatus that will be mounted on the station’s exterior to study Earth’s atmosphere from above. Over the course of about a month, the crew will unload the capsule and then fill it back up with payloads for return to Earth.

SpaceX is leasing Launch Complex 39A under the terms of a 20-year agreement with NASA – a deal that was sealed in 2014 after a competition with Blue Origin, the space venture founded by Amazon billionaire Jeff Bezos.

In addition to 39A, SpaceX has been using Launch Complex 40 at Cape Canaveral Air Force Station. That pad was heavily damaged when a Falcon 9 blew up during preparations for launch last September. It’s now under repair.

Eventually, SpaceX plans to launch crews to the space station from Pad 39A, as well as the company’s yet-to-be-tested Falcon Heavy rocket.

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