Brian Cox and Dara O Briain return for their third night celebrating space and astronomy, with more updates from British astronaut Tim Peake. This time they explore what keeps Tim and his International Space Station crew-mates safe in the hazardous environment of space. Brian and Dara also welcome a very special guest to take the gravity challenge - and find out what it would feel like to walk on Mars and the Moon.Roving reporter Liz Bonnin once more reports live from the European Astronaut Centre in Cologne, where she tests whether comedian John Bishop has the 'right stuff'. A lifelong astronomy fan, John will be strapped into a giant centrifuge machine to experience how future astronauts will simulate gravity during missions into deep space.Brian and Dara are joined in the studio by Dame Jocelyn Bell-Burnell, to hear how she discovered the first pulsar star - giving astronomers all over the world one of their most precious tools for studying the universe. They also find out whether Stargazing viewers have discovered any new pulsars in their three-night search, training Jodrell's famous telescope onto them to reveal exactly what has been discovered, and how much that means to astronomers.