Why Elon Musk's SpaceX is launching astronauts for Nasa

Elon Musk's SpaceX is flying people to and from the International Space Station (ISS), using the Crew Dragon vehicle. But why is Nasa paying a private company to carry its astronauts? To understand the background to the Crew Dragon missions, we need to go back almost 20 years to a tragic accident. On 1 February 2003, the space shuttle Columbia broke apart while re-entering the Earth's atmosphere. All seven astronauts aboard perished in the disaster. The loss of Columbia and its crew was the trigger for a dramatic shift in direction for America's human spaceflight programme. On 14 January 2004, President George W Bush announced that the space shuttle would be retired after...