Dr. Jerrod Hofferth, von Kármán Gas Dynamics Facility Wind Tunnel D lead engineer, works on a freestream characterization rake, used to determine Mach Number Uniformity, positioned in the Tunnel D test cell June 5 at Arnold Air Force Base. The tunnel was reactivated earlier this year and is operated by the Air Force Research Laboratory High Speed Experimentation Branch. (U.S. Air Force photo by Jill Pickett)