Abstract
Fundamental lateral mode frequency of a spacecraft is determined experimentally by performing a base excited vibration testing. For the above vibration testing, the spacecraft is mounted on the slip table of the shaker system. It is shown in this work that even if the test fixture is quite stiff, the fundamental lateral mode of the spacecraft can be influenced by the slip table system. The frequency obtained in the test is lower than the base fixed frequency. In this mode, even though the test fixture does not undergo bending, the slip table undergoes bending resulting in rotation of the test fixture. The stiffness of the bearing and the bending stiffness of the slip table are the causes of reduction in stiffness. A mathematical model that represents this behavior is developed for two typical shaker-slip table systems, one having a capacity of about 150 kN force and the other about 300 kN force. It is seen that the test system can cause a drop of about 3 Hz for a 3000 kg class of spacecraft, while using 150 kN shaker system. This is quite significant as their frequencies are in the range of 12–15 Hz.
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Abbreviations
- \({f}_{n}\) :
-
Natural frequency of the system
- \(k\) :
-
Stiffness of the spring
- \({k}_{1, }{ k}_{2}\) :
-
Stiffnesses of the two springs
- \(m\) :
-
Mass of the system
- \(I\) :
-
Mass moment of inertia of the system
- \(x\) :
-
Coordinate, along the normal to the slip table
- \(y\) :
-
Coordinate, along the direction of motion of the slip table
- \({y}_{1, }{ y}_{2}\) :
-
Deflections of two springs
- \(z\) :
-
Coordinate, normal to the direction of motion of the slip table
- \(\theta\) :
-
Angle of rotation
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Acknowledgements
Several experiments that were needed for this work were done with the help of colleagues of Vibration Laboratory. This work is concluded after observing and analyzing the results of dynamic tests and dynamic analyses of large number of spacecrafts. In this regard the author wishes to thank colleagues of Structures Group and Vibration Laboratory. Thought process along this direction was initiated by Dr. P. S. Nair, earlier Group Director of structures group.
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K, R. Influence of Slip Table of the Shaker System on the Experimentally Obtained Fundamental Lateral Mode Frequency of a Spacecraft. Exp Tech 48, 205–217 (2024). https://doi.org/10.1007/s40799-023-00652-2
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DOI: https://doi.org/10.1007/s40799-023-00652-2