Live coverage: SpaceX cargo capsule returns to Earth

Two Chinese astronauts are busy with medical experiments and other duties as they near the halfway mark of a month-long stay aboard the Tiangong 2 space lab, according to state media reports.

SpaceX chief executive Elon Musk on Tuesday outlined an ambition to send humans to Mars with methane-fueled reusable spaceships and the largest rocket ever built, an effort he said will likely require government support and initially cost billions of dollars to develop and test.

In this time-lapse video, a Falcon Heavy rocket is lifted into position atop launch pad 39A at the Kennedy Space Center in readiness for a pre-flight test firing of its 27 Merlin main engines.