Former NASA astronaut Dr Kathy Sullivan, the first American woman to walk in space, has made history again by travelling to the deepest known point on earth. Last Sunday, the 68 year-old space-walker and oceanographer travelled seven miles below the surface of the Pacific ocean to reach the Challenger Deep, the ocean's lowest spot, becoming the first woman to do so. Mark Coles talks to her fellow astronauts as he profiles one of the world’s most intrepid explorers.

Producer: Viv Jones