Vibration-test evaluation of an ULLAGE solid-propellant rocket motor

The mission of the ULLAGE motor is to maintain a positive acceleration of the Saturn rocket during the period between burnout of the first stage and ignitiion of the second stage. The eight ULLAGE motors attached to the Saturn second stage are fired during separation from the first stage. They must withstand intense sound levels and vibrations transferred through the first stage and the interstage structures. Vibration tests were performed on an inert ULLAGE motor to safely educe the approximate response of the design configuration. The results served as a basis for improved definitions of the control parameters in subsequent vibration tests performed during the development program. The motor was tested while subjected to harmonic (sinusoidal) displacing excitation, as well as to a Gaussian distribution of random vibration. The transmissibilities and power spectral densities were obtained for forcing functionals in the longitudinal, radial and tangenital directions. Summaries of all the vibration tests were prepared and the critical frequencies were enumerated and discussed.