Effect of Acoustic Vibration on the Satellite Structure at Launch Stage Mechanical Engineering Department University of Salahaddin/Iraq-Erbil Abstract The launch of satellite generates extreme conditions, such as vibrations and acoustics that can affect the launch pad, satellite, and their payloads. The noise at launch and liftoff causes intense acoustic loads. These acoustic loads are the result of an intense acoustic environment generated by the interaction of the rocket-engine exhaust stream mixing with the atmosphere. Acoustic load among the most critical quantity measures before all the satellite when launches to space. Vibrations that produced by use one side of the satellite structure can contain valuable information about the state of acoustic on the satellite. The work was planned and curried out in such a way to provide detailed information on effect of the acoustic vibration on one side of the plate in satellite structure. The focus of this study is to find a correlation between acoustic and the plate vibration. A Vibrometer measurement device was used to measure displacement and velocity in horizontal directions to obtain the vibration information. Stress in (x, y)-directions on the plate are measured by applying a strain gage technique. The ranges of acoustic parameters in the present study were quite limited: starting sound pressure level (80, 90, 100, and 108 dB), frequency of sound (31.5, 63,125, 250, 500, 1000, 2000, 4000, 8000 Hz) and strain gauge directions (horizontal, and vertical). In this study also the finite element technique were used by software ANSYS to appearance acoustic parameters, to analytical predictions. Structural mode shapes and showed high level and low level of deformation and stress at each place on the plate. Keywards: Satellite Structure, acoustic vibration, Launch Stage Introduction Launching satellites is the launch vehicle-induced vibration and shock environment that a satellite must endure on its trip to orbit. During the launch of space vehicles, there is a large external excitation generated by acoustic and structural vibration. This is due to acoustic pressure fluctuations on the vehicle fairing caused by the engine exhaust gases. This external excitation drives the fairing structure and produces large acoustic pressure fluctuations inside the fairing cavity. The acoustic pressure fluctuations not only produce high noise levels inside the cavity but also cause damage such as structural fatigue, and damage to, or destruction of, the payload inside the fairing. [1]. Rocket motors generate tremendous acoustic energy at liftoff. Turbulent mixing of the hot exhaust gas with the surrounding air is the dominant acoustic source. The exhaust gas may also have aerodynamic shock waves, which further add to the noise. Combustion instability and rough burning may also contribute to the noise Consider a rocket vehicle which has a payload enclosed in a nose cone firing [2]. The acoustic energy propagates to the payload fairing. The energy is then transmitted through the fairing wall to the enclosed air volume. The payload may be sensitive to the transmitted acoustic excitation, especially if the payload has solar panels or delicate instruments. Excessive vibration and shock can cause permanent damage to satellite electronics, optics, and other sensitive equipment. An excellent alternative is to reduce the launch loads through the use of isolation systems. Because, the primary source of structural vibrations and internal loads during launch is due to these acoustic loads. Once the vehicle achieves supersonic speed, the effect of rocket exhaust noise are generally minimal compared with the turbulent flow noise excitation [3]. Excessive noise levels inside the payload bays of launch vehicles are blamed for as many as 60% of first day satellite failures. It is claimed that 40% of the mass of a satellite is present just to enable the satellite to survive the harsh vibro-acoustic launch environment. If payload bay interior noise levels could be reduced, the probability of satellite survival would increase and the mass of a satellite could be reduced, which has obvious financial benefits for both the cost of a satellite and the associated launch costs [4]. Sharon and Chang [1996] describe the force limited vibration test of the Cassini spacecraft. Over a hundred acceleration responses were monitored in the spacecraft vibration test, but only the total axial force is used in the control loop to notch the input acceleration. The instrument force limits derived with the semi-empirical method are generally equal to or less than those derived with the two-degree-of- freedom method, but are still conservative with respect to the interface force data measured in the acoustic test [5]. John C. Forgrave, ET [1997] describes a method for optimizing acoustic and random vibration trials to reduce cost and schedule, without incurring undue risk to the hardware depending on the surface area, mass, and geometry of the test object, one vibration test is normally more effective as a failure screening mechanism. Random vibration is found to be more effective in spring-mass systems with input frequencies ranging from 20 to 2,000 Hz. Investigation the effects sound pressure level and frequencies on the spacecraft when become acoustic vibration and random vibration, when there was used sound pressure level to 135 dB [6]. Terry Scharton [1998] Instead of conducting the acoustic test with the spacecraft in a reverberant room, the test was conducted with the spacecraft mounted on a shaker slip-table in a nearly anechoic, vibration test cell. The spacecraft was surrounded with a three-meter high ring of large, electro-dynamic speaker, spaced approximately 1.3 meters away from the two-meter diameter, 900 kg spacecraft. The thirty-one speaker cabinets were driven audio amplifier power, the acoustic specification, with an overall sound pressure level of 135 dB. [7]. Craig L. Stevens [2002] Investigated several materials and methods used to optimize the structural properties of spacecraft assemblies. This thesis was described the design of the spacecraft and the entire satellite configuration, and applied the theory to results of the finite element analysis to arrive at the design. [8]. Aidan Bettridge [2004] deals with the investigation into the design and analysis of developing the structural subsystem of a picosatellite capable of carrying a scientific payload into orbit. The design of the satellite is constrained by the specifications defined by the Cube Sat Standards. By using finite element analysis computer programs Strand7. There was analyzed acoustic vibration and random vibration of one side of plate and all sides with them (box) [9]. K. Renji [2006] Vibration energy transfer in a system of three plates separated by a small distance and connected at a few discrete points, like solar panels in a spacecraft, is investigated. Coupling loss factors are obtained experimentally using the power injection technique. The system is then subjected to the acoustic excitation in a reverberant chamber. The measured responses of the inner plate are significant. When the system is subjected to mechanical excitation the measured responses of the inner plate closely match with the estimated responses. [10]. Mir Md. Maruf [2008] establishes theoretical and numerical models for the prediction of external sound pressure loading on composite structures representing launch vehicles, such as a large composite International Conference on Modeling and Simulation (MS09) India 1-3 Dec 2009 Department of Electronics and Communication Engineering College of Engineering Trivandrum, India 32 AbdulRahman Bahaddin Shakir Safeen Yaseen Ez-Deen