NASA Astronaut and Expeditions 23 and 24 Flight Engineer, Tracy Caldwell Dyson, speaks at a Women's History Month event at NASA Headquarters, Wednesday, March 16, 2011 in Washington. The event entitled Women Inspiring the Next Generation to Reveal the Unknown is a joint venture with NASA and the White House Council on Women and Girls. Caldwell Dyson recently returned from a six-month stay aboard the International Space Station. Photo Credit: (NASA/Carla Cioffi) NASA Identifier: nasahqphoto-5532524853