Elon Musk is never one to shy away from setting ambitious goals. In fact, the billionaire's most ambitious goal might just be the one he often talks about the most: going to Mars.

On Wednesday, Musk and his private spacecraft company, SpaceX, nearly checked off a historic milestone that could put him another step closer to one day achieving that goal. That milestone would be SpaceX's first-ever manned space mission. The company was set to launch two NASA astronauts on a flight taking them to the International Space Station, but SpaceX postponed the launch at the last minute due to inclement weather. SpaceX and NASA will now look to push the launch to Saturday, May 30, at 3:22 p.m. ET.