The propulsion and the structure of a space vehicle form a feedback loop through inertial coupling referred to as the pogo phenomenon and experienced with the Thor , Titan, and Apollo-Saturn V space vehicles.
Von Pragenau suggests to Sparkman that residents of Huntsville should display American flags outside their homes and businesses at the same moment that "astronaut Neil Armstrong will plant the American flag onto the lunar soil." He wrote a similar letter to Huntsville mayor Joe Davis.