Over the past weekend, SpaceX made its fourth attempt at successfully launching and landing one of its Falcon 9 rockets on a drone ship at sea. As with the previous three occasions, the Falcon 9 rocket failed, with CEO Elon Musk noting that the rocket "landed hard" on the drone ship.

Rocket landed hard on the droneship. Didn't expect this one to work (v hot reentry), but next flight has a good chance.

— Elon Musk (@elonmusk) 5 March 2016

The SpaceX founder remains optimistic however, with high hopes that the next test has a far greater chance of success than this latest one. It appears as if speed on reentry is the biggest problem facing SpaceX at the moment, as their attempt prior to this one suffered a similar fate, causing a spectacular explosion in the process.

The company's plans have not been dented by this latest failure however, with a resupply mission for the International Space Station set to go ahead in the next couple of weeks. A new test date for its Falcon 9 landing mechanism has not been detailed though. It appear as if SpaceX still has some work to do, with rivals Blue Origin's rockets already capable of making landings after launch, albeit at half the altitude of the Falcon 9.