One of the design challenges on many spacecraft is addressing the structural response to the acoustic loads coming from the launch vehicle rocket motors. Payloads of the launch vehicles, such as satellites, can be greatly affected by these acoustic loads. For many existing launch vehicles these loads have been addressed by tedious hand calculations or by acoustic tests which occur late in the program when design changes are very difficult to implement. As the commercial space program and global communication business demand lower cost launches and higher performance from launch vehicles, the conservatism in this approach is no longer acceptable.

ATA has extensive experience in the prediction of sound and vibration levels for launch vehicles, spacecraft and aircraft. This experience includes the prediction of external acoustic levels at launch using semi-empirical methods as well as external fluctuating pressures using both wind tunnel data and semi-empirical methods. We also have extensive experience predicting vibration responses to acoustic inputs using a combination of Finite/Boundary Element Model (FEM/BEM) methods, Statistical Energy Analysis (SEA) and Hybrid methods. We are on the leading edge of applying the most advanced methods to the prediction of vibro-acoustic responses, including the most recent Hybrid methods implemented in the VA-one software package.

Tools

ATA uses a combination of tools for vibro-acoustic analysis. These include spreadsheets and Matlab implementations of various semi-empirical methods; Nastran for FE analysis; RAYON for BE analysis; and VA-one for both SEA and Hybrid analysis. We have also developed a number of Matlab-based tools for direct excitation of FE models due to both acoustic diffuse fields and turbulent boundary layers as well as for the post-processing of FEM/BEM acoustic responses.

Project Experience

Aircraft Interior Noise — For a small business jet, we used SEA methods to predict the interior noise due to both engine and turbulent boundary layer excitations. The models were correlated to flight test data and used to recommend modifications to the aircraft to reduce interior noise levels.

Spacecraft Panel Vibration — Calculated spacecraft solar and equipment panel vibrations and fluctuating stress levels due to excitation by a diffuse acoustic field and compared with test results. A variety of methods were used including direct diffuse field excitation of a FEM, a Boundary Element model, and a Statistical Energy Analysis model.

Spacecraft Reflectors — Calculated vibration and stress levels on a number of different lightweight reflectors using both BEM/FEM and SEA methods.

Launch Vehicle Fairing Stress — Calculated fluctuating ply-by-ply stress levels in a composite solid rocket motor fairing due to launch loads using a BEM/FEM approach.

Rocket Engine Nozzle Stress — Calculated detailed stress levels including local stress concentrations in a lightweight rocket nozzle due to diffuse field acoustic excitation

Small Launch Vehicle Vibro-Acoustic Predictions — Calculated external acoustic levels for both liftoff and transonic flight along with interior noise and vibration levels for a number of small- to mid-size launch vehicles. Methods included both SEA and Hybrid FEA/SEA methods and data has been correlated to both flight and acoustic test levels.

Vibro-acoustic Predictions on the Crew Exploration Vehicle — Calculated external fluctuating pressures during transonic flight for the CEV based on wind tunnel test data from the Apollo/Saturn program. Also predicted internal noise and vibration levels for both liftoff and transonic flight using SEA, Hybrid and direct FEA methods.

Techincal Papers

Baker, M., J. Hansen, and F. M. Payne, "Impact of Dynamics on the Design of the RL10-2 Extendible Carbon-Carbon Exit Cone." [folder 394]

Baker, M., P. Blelloch, T. Burton, and F. M. Payne, "Coordinated Use of FEM/BEM and SEA for the Acoustic Response of Delta III RL10B-2 Deployable Nozzle." [folder 393]