Last updated at 17:00

Pictures: Dream Chaser mini-shuttle gets 2016 launch date

The mini space shuttle Dream Chaser has a launch date for its first flight - 1 November 2016. It's a possible replacement for Nasa's space shuttles.
At nine metres long, the Dream Chaser is much smaller than previous shuttles, but it can carry seven people into space. This artist's impression shows the spacecraft on top of an Atlas V rocket ready for launch.
An artist's impression of the Dream Chaser
This is the Dream Chaser! It's one of three possible replacements for Nasa's space shuttles and has been given its first orbital flight launch date.
The Dream Chaser
The winged vehicle will blast into space from Florida's Kennedy Space Centre on 1 November 2016. It's been designed by the Sierra Nevada Corporation (SNC) to restart human spaceflight operations in America following the retirement of their space shuttles in 2011.
The Dream Chaser, front view
This artist's impression shows the Dream Chaser spacecraft docking with the International Space Station. Two other companies, Boeing and SpaceX, have also designed space shuttles for Nasa.
An artists impression of the Dream Chaser
The Dream Chaser's debut flight will be unmanned, but if it goes well, then SNC hopes to send its first manned mission into space in 2017.
The Dream Chaser
The Dream Chaser's mission is to provide Nasa with a safe, reliable transportation service for crew and cargo to the International Space Station and back to Earth. The vehicle has been undergoing tests before its launch - this picture shows a sky crane helicopter lifting the spacecraft into the air for a test flight.
The Dream Chaser