Nasa has said it will return a four-person crew aboard the International Space Station (ISS), cutting short their mission a month early because of a "serious medical condition" affecting one of the astronauts.

Five American astronauts have 10 spacewalks under their belt to date: Bob Behnken, Stephen Bowen, Chris Cassidy, Michael Lopez-Alegria and Peggy Whitson. The world record is 16, held by cosmonaut Anatoly Solevyev.

SLS and the Orion spacecraft are fully stacked together inside NASA’s Vehicle Assembly Building (VAB) at Kennedy Space Center. Once final tests are complete, the launch vehicle will be rolled out onto the pad at Launch Complex-39A, which should take about 10 hours.