Members of Team Valkyrie, NASA Johnson Space Center, try to repair Valkyrie after it stopped responding during the wall task at the Homestead-Miami Speedway, Friday, Dec 20, 2013, in Homestead, Fla. Seventeen teams from the United States, China, Japan, and Korea are participating in the DARPA Rpbotics Challenge Trials. The event is a test of some of the most advanced robots in the world. (AP Photo/Alan Diaz)
