This photo provided by SpaceX shows the first stage of the company's Falcon rocket after it landed on a platform in the Atlantic Ocean just off the Florida coast on Friday, May 6, 2016, after launching a Japanese communications satellite. (SpaceX via AP)

For the second month in a row, the aerospace upstart SpaceX landed a rocket on an ocean platform early Friday, this time following the successful launch of a Japanese communications satellite.

A live webcast showed the first-stage booster touching down vertically in the pre-dawn darkness atop a barge in the Atlantic, just off the Florida coast. The same thing occurred April 8 during a space station supply run for NASA. That was the first successful landing at sea for SpaceX, which expects to start reusing its unmanned Falcon rockets as early as this summer to save money and lower costs.

Because of the high altitude needed for this mission, SpaceX did not expect a successful landing. But it was wrong. As the launch commentator happily declared, "The Falcon has landed."

SpaceX founder and chief executive Elon Musk was even more exuberant. "Woohoo!!" he exclaimed in bold letters via Twitter.

"May need to increase size of rocket storage hangar," he added in a tweet.

Musk said this was a three-engine burn for the booster's return, "so triple deceleration from the last flight." Before liftoff from Cape Canaveral, Florida, he put the chances of a successful touchdown at "maybe even" because the rocket was coming in faster and hotter than last time.

This photo provided by SpaceX shows the first stage of the company's Falcon rocket after it landed on a platform in the Atlantic Ocean just off the Florida coast on Friday, May 6, 2016, after launching a Japanese communications satellite. (SpaceX via AP)

Musk contends rocket reusability is key to shaving launch costs and making space more accessible.

SpaceX is the only company to recover a rocket following an orbital launch. It achieved its first booster landing—on solid ground at Cape Canaveral Air Force Station—in December. A landing at sea proved more elusive and required several tries.

Blue Origin, led by another wealthy high-tech entrepreneur, Jeff Bezos of Amazon.com, has landed and even reflown its booster rockets, but those did not put anything into orbit.

A SpaceX Falcon 9 rocket lights up the sky during a launch from the Cape Canaveral Air Force Station's Launch complex 40 early Friday morning, May 6, 2016, in Fla . Aboard is the JCSAT-14 communications satellite. SpaceX has done it again. For the second month in a row, the aerospace company landed a rocket on an ocean platform, this time following the launch of a Japanese communications satellite. (Craig Rubadoux/Florida Today via AP)

Following last month's landing, Musk said he plans to fly that booster again, possibly as soon as June. The first recovered booster, from December, will grace the entrance of SpaceX headquarters in Hawthorne, California.

Already in the delivery business for NASA, SpaceX hopes to start transporting U.S. astronauts to the International Space Station by the end of next year in the company's next-generation Dragon capsules. But its ultimate goal is Mars.

In a groundbreaking announcement last week, Musk said his company will attempt to send a Red Dragon to Mars in 2018—and actually land on the red planet. His ambition is to establish a city on Mars.

He also runs Tesla Motors, the electric car company.

SpaceX's Falcon 9 rocket launches the JCSAT-14 communications satellite at Cape Canaveral, Fla, early Friday, May 6, 2016. The Falcon 9 first stage also landed on a droneship while the second stage continued on, delivering the spacecraft to a Geosynchronous Transfer Orbit. (SpaceX via AP)

SpaceX's Falcon 9 rocket launches the JCSAT-14 communications satellite at Cape Canaveral, Fla, early Friday, May 6, 2016. The Falcon 9 first stage also landed on a droneship while the second stage continued on, delivering the spacecraft to a Geosynchronous Transfer Orbit. (SpaceX via AP)

Explore further SpaceX to launch Japanese satellite early Friday

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