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Payload noise suppression using distributed active vibration absorbers

The authors are developing a cost- and weight-effective means for achieving an improved low- and mid-frequency acoustic environment in payload fairings for rockets at lift-off. The solution will be an active noise control system with an optimum selection of distributed active vibration absorbers (DAVAs) and acoustic actuators. High sound pressure inside a launch vehicle fairing during lift-off can damage delicate equipment in the payload. Space launch vehicle payload noise is a very important problem in the successful launch and deployment of space instruments and equipment. Measurements taken during the first few seconds of launch show very high sound pressure level (SPL) in the low frequency range of 60 to 250 Hz. High SPL is a severe problem because interior noise impinges on the instruments and equipment in the payload and can lead to their vibrational failure. Engineers have made moderate progress in addressing this problem by strengthening the instruments and by applying passive noise control treatment to the fairing. Both strategies incur significant penalties of added weight and financial cost and reduced allowable payload size. For further progress in suppressing low-mid frequency noise, another way is needed. The authors are developing a hybrid passive/active noise control system based on emerging technology of distributed active vibration absorbers (DAVAs). DAVAs are constructed from acoustic foam and area-distributed actuators. Passively it behaves as a tuned mass damper at low frequencies and a viscous damper at high frequencies. Actively a DAVA produces mechanical forces that are directed to reduce fairing vibrations.