The third attempt by private space company SpaceX to land its Falcon 9 booster rocket back on Earth intact has ended with an explosion.

The company, which did not have permission to land the rocket on land, made the attempt on an unmanned barge in the Pacific Ocean off California on Sunday.

A video released by the company's founder Elon Musk shows the rocket navigating its way within 1.5 metres of the target and touching down, but without one of the rocket's four legs deployed, it then topples over and explodes.

NASA satellite launched to monitor global warming

"Touchdown speed was OK, but a leg lockout didn't latch, so it tipped over after landing," Musk tweeted shortly after the test.

The landing attempt was the second part of a mission which earlier saw the rocket carry the Jason-3 climate satellite into orbit, from where it will measure the height of the sea far below to within just 4cm.

The $180m mission is expected to provide US and French scientists with vital data to track long-term changes to climate and the ocean's role in global warming.

SpaceX will now examine what remains of the rocket, in particular the suspect landing leg.

Musk was quick to speculate on Instagram that weather conditions at launch may have played a role. "Root cause may have been ice buildup due to condensation from heavy fog at liftoff," he posted

Reusable rockets

The company is eager to make its booster rockets reusable; each one costs around $16m and until now, have only been able to be used for one launch before crashing into the ocean.

SpaceX has been testing its landing technology on the rockets since April last year, when it also made an unsuccessful attempt to land on a barge.

Referring to that test, which resulted in the rocket breaking into hundreds of pieces, Musk tweeted that "at least the pieces were bigger this time!"

Source: Al Jazeera