by NASA/Marshall Space Flight Center
Published 10/1/1968 (October 1st, 1968)
Dr. von Braun inside the KC-135 in flight. The KC-135 provide NASA's Reduced-Gravity Program the unique weightlessness or zero-g environment of space flight for testing and training of human and hardware reactions. The recent version, KC-135A, is a specially modified turbojet transport which flies parabolic arcs to produce weightlessness periods of 20 to 25 seconds and its cargo bay test area is approximately 60 feet long, 10 feet wide, and 7 feet high.
From www.archive.org (I absolutely love that website--if you have a chance, please take a look at it!!)