SpaceX failed to land the first stage of its Falcon 9 rocket on a floating platform in the Pacific Ocean on Sunday, marking the fourth time it has missed the mark."First stage on target at droneship but looks like hard landing; broke landing leg," the California-based company said on Twitter.SpaceX said it lost contact with its live video link of the floating barge, or droneship, before the rocket came in for a landing, so no images were immediately available. A commentator on SpaceX's live webcast said video would be made available in the coming hours."Unfortunately we are not standing upright on the drone ship at the moment but the good news here is that the primary mission is still on track," said the commentator, referring to the launch of the US-French oceans satellite, Jason-3.SpaceX is trying to land its rocket back on Earth so it can re-use the parts in the future, as the company headed by Internet entrepreneur Elon Musk tries to make spaceflight cheaper and more sustainable than before.SpaceX succeeded in landing its Falcon 9 first stage -- the long towering portion of the rocket -- on solid ground at Cape Canaveral, Florida in December.Even though an ocean landing is more difficult, SpaceX says it needs to perfect the technique so it can bring back its rockets in all kinds of situations.