SpaceX lands rocket on ocean platform for first time

Images of the tall, narrow rocket gliding down serenely onto a platform that SpaceX calls a droneship sparked applause and screams of joy at SpaceX mission control in Hawthorne, California.

"The first stage of the Falcon 9 just landed on our Of Course I Still Love You droneship," SpaceX wrote on Twitter, after launch from Cape Canaveral, Florida at 4:43 pm (2043 GMT).

NASA spokesman George Diller confirmed that the rocket had successfully landed, just minutes after the Falcon 9 propelled the unmanned Dragon cargo craft to orbit, carrying supplies for astronauts at the International Space Station.

SpaceX has once before managed to set the rocket down on land, but ocean attempts had failed, with the rocket coming close each time but either crashing or tipping over.

Speaking to reporters afterward, SpaceX CEO Elon Musk said that being able to return costly rocket parts for repeated use, instead of jettisoning them into the ocean after each launch, will make spaceflight less expensive and less harmful to the environment.

"It is just as fundamental in rocketry as it is in other forms of transport such as cars or planes or bicycles or anything," said Musk, who also runs Tesla Motors.

Musk said it costs around $300,000 to fuel a rocket, but $60 million to build one.

"If you have got a rocket that can be fully and rapidly reused, it is somewhere on the order of a 100-fold cost reduction, in marginal costs," he said, adding that he hoped his competitors would follow suit.

President Barack Obama led the praise, tweeting: "Congrats SpaceX on landing a rocket at sea. It's because of innovators like you & NASA that America continues to lead in space exploration."

Also on Twitter, Canadian astronaut Chris Hadfield said: "Landed! That is amazing! World-leading ability, proven.

Friday's breakthrough came after a closely watched return-to-flight mission, SpaceX's first cargo delivery since June 2015, when the Falcon 9 exploded just over two minutes after liftoff, destroying the rocket and the supply ship.

SpaceX blamed the blast on a faulty strut in the Falcon 9's upper booster, which allowed a helium bottle to snap loose, causing the explosion of the rocket, cargo ship and all its contents.

It has since upgraded its Falcon 9 rocket and changed its protocol to avoid a repeat.

This time, the gumdrop-shaped capsule was packed with nearly 7,000 pounds (3,100 kilos) of supplies for the astronauts living in orbit.

The Dragon's cargo includes an inflatable space room astronauts will test in microgravity.

Known as the Bigelow Expandable Activity Module, the chamber will be temporarily attached to the space station.

Lab mice for experiments and lettuce seeds for growing at the orbiting outpost were also included in the spacecraft, which should arrive at the International Space Station early Sunday.

Musk said the rocket was being welded onto the droneship with metal shoes, so as not to tip over as it made its way back to land.

Next, the booster will undergo a series of tests, including 10 static fires on the launchpad, before engineers decide if it is in good enough shape to fly again.

If so, the next launch of the same booster could be in the next two to three months, Musk said.

"In the future, hopefully we will be able to relaunch them in a few weeks."

In the meantime, SpaceX will keep working on perfecting its landing techniques, whether on ocean or solid ground, since both options need to be available to suit different types of missions.

Musk said about half of SpaceX's rockets will need to land at sea, and it might take a few years to work out all the kinks.

"But I think it is proven that it can work," he said.