Arnold Engineering Development Complex test engineers, from left, Yancee Burchett, Jillian Sears and Capt. Brian Gatzke, monitor a nozzle test in the Sea Level 2 Test Cell, Dec. 17, 2020, at Arnold Air Force Base, Tenn. The test team was using small-scale models of nozzles to investigate their acoustic properties. (U.S. Air Force photo by Jill Pickett)