Active structural-acoustic control for composite payload fairings

Launch loads, both mechanical and acoustic, are the prime driver of spacecraft structural design. Passive approaches for acoustic attenuation are limited in their low frequency effectiveness by constraints on total fairing mass and payload volume constraints. Active control offers an attractive approach for low frequency acoustic noise attenuation inside the payload fairing. Smart materials such as piezoceramics can be exploited as actuators for structural-acoustic control. In one active approach, structural actuators are attached to the walls of the fairing and measurements from structural sensors and/or acoustic sensors are fed back to the actuators to reduce the transmission of acoustic energy into the inside of the payload fairing. In this paper, structural-acoustic modeling and test results for a full scale composite launch vehicle payload fairing are presented. These analytical and experimental results fall into three categories: structural modal analysis, acoustic modal analysis, and coupled structural-acoustic transmission analysis. The purpose of these analysis and experimental efforts is to provide data and validated models that will be used for active acoustic control of the payload fairing. In the second part of the paper, this closed-loop acoustic transmission reduction is implemented and measured on a full-scale composite payload fairing.