LINE OF LEADERS Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, speaks with Defense Secretary Robert M. Gates before the U.S. Strategic Command change-of-command ceremony on Offutt Air Force Base, Neb., Jan. 28, 2011. Air Force Gen. Kevin P. Chilton, who was relieved by Gen. C. Robert Kehler, retired after a 34-year career in which he was the first former astronaut to achieve the four-star general officer rank. SHARE: Download: Full Size (0.06 MB) Credit: VIRIN: 743136-F-JHP79-294.jpg Photo Gallery