The late Dr. David E. Walker, center, a beloved former Air Force Research Laboratory, or AFRL, director and vice commander, is pictured during a visit to the Air Force Research Laboratory’s Rocket Propulsion Division at Edwards Air Force Base, Calif., Sept. 23, 2015. At the time of this visit, Walker served as deputy assistant secretary of the Air Force for science, technology and engineering in the Office of the Assistant Secretary of the Air Force for Acquisition. According to his former colleagues, in this role Walker advocated passionately for AFRL and worked tirelessly to maintain and protect its defense budget. (U.S. Air Force photo / Kenji Thuloweit)