A smoke ring forms when the pressure from an unarmed Minuteman III ignites in its underground silo March 23, 2015, at Vandenberg Air Force Base, Calif., during an operational test launch. The ring does not occur during above ground rocket startups, like those on space lift vehicles because the pressure and smoke are able to escape outward and away from the engine, versus being forced up through the launch tube. (U.S. Air Force photo by Joe Davila)