Ludwieg Tube Group - GALCIT The Ludwieg Tube is a Mach 2.3 facility located at the California Institute of Technology, in Pasadena, CA. It is part of the Graduate Aeronautics Laboratory. The facility has a test time 80 milliseconds. The concept of a Ludwieg Tube was first proposed in 1955 by Hubert Ludwieg, a German scientist. The beauty of the Ludwieg Tube is that it provides clean supersonic flow with relative ease and low cost. Below is a design drawing of the entire facility: A close-up view of the nozzle section: Below is an image of Mach waves throughout the test section, showing the uniformity of the flow: (Schlieren image by J. Klamo, M. El-Naggar, M.-H. Tan)