Dynamic Analysis & Testing of a Spacecraft/Probe Model

Paper number

IAC-05-C2.P.18

Author

Mr. Farouk Jivraj, Imperial College London, United Kingdom

Year

2005

Abstract

Structural tests are vital to find out the effects of static and dynamic loads on a structure. Dynamic loading is very important in structures designed to fly as a phenomenon known as flutter can cause structural failure. Performing a vibration test will help us to understand the structures better therefore preventing both the failure of the spacecraft/probe while in flight and the loss of an expensive craft/probe.

The structure of the spacecraft can be modelled using idealisations. Either a point mass idealisation can be used or a lumped mass idealisation. A point mass idealisation does not take into account rotational inertias and models the structure using weightless bars with appropriate bending stiffness; while the lumped mass idealisation includes rotational inertias. From the idealisation, matrix equations can be produced which represent the structure. Theoretical mode shapes and resonance frequencies of the structure in questioned can then be obtained. At the resonance frequencies the motion is a principal mode of vibration. The number of natural frequencies and principal modes that a system possesses is equal to the number of degrees of freedom of the structure. 

Though it is useful to have theoretical values for the mode shapes and frequencies at which large vibrations will occur (resonance frequencies), damping in the spacecraft will have a significant affect on it structural response. This is not taken into account in the theoretical values as it is usually very low and so it is assumed to be zero as a first approximation which therefore simplifies the matrix equations. Therefore it is better to conduct an actual structural experiment using the idealised structure to represent the spacecraft. 

By conducting an experiment we can accurately enforce the damping on the idealised structure, which is present on the real spacecraft structure. This will produce fairly accurate values of the resonance frequencies. This will allow the engineers to prevent the spacecraft from being exposed to these frequencies, therefore preventing its structural failure. Structural testing is an essential part of space technology production. Without it, many missions would have not resulted in a successful outcome. Hence, it is important that as much information as possible is obtained about how the spacecraft/probe will respond to its flight conditions before it is sent out into actual flight.

Abstract document

IAC-05-C2.P.18.pdf

Manuscript document

IAC-05-C2.P.18.pdf (🔒 authorized access only).

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