One of the pilots who has flown the adapted shuttle-carrying 747 has spoken to the BBC about the challenge of flying with such an unusual load.

Research pilot Bill Brocket has been with Nasa for 25 years, and while he did not fly Discovery over Washington on her final flight, he has flown the Shuttle Carrying Aircraft some 15 times before.

He told BBC Radio 5 live: "There are a few [planes] that fly at heavier weights, but none of them have the drag that the shuttle imposes."