Outside machinists Todd Robison, top, and Troy Jernigan inspect a ball screw for one of the jacks on the plenum side of the nozzle of the Arnold Engineering Development Complex 16-foot supersonic wind tunnel Sept. 25, 2020, at Arnold Air Force Base, Tenn. These jacks are driven to precise locations by the nozzle motors to set correct contours for creating supersonic flow on the air side of the nozzle. (U.S. Air Force photo by Deidre Moon) (This photo has been altered by obscuring a badge for security purposes.)