A launch pad problem has prompted SpaceX to delay a flight to the International Space Station to replace Nasa's two stranded astronauts.

Two NASA officials have weighed in on the public dispute over when and how to bring home Butch Wilmore and Suni Williams, who have been on the International Space Station since June.

Elon Musk called a former SpaceX pilot "retarded" for refuting the billionaire's claim that the two astronauts at the International Space Station were "abandoned" (which the astronauts themselves deny).