Master Thesis - OUFTI-1

Figure 4.14: Example of spacecraft stiness requirements for dierent launchers
4.3.3 Experimental test of the OBC 2 card
In this section, the description of the experimental test performed on the OBC 2 card,
will be explained. Three main parameters have to be dened for a vibration test: the
boundary conditions (the support), the type of excitation and the acquisition system.
Each of these parameters has a great inuence on the results obtained and so, they have
to be chosen carefully.
Boundary conditions
The choice of the support used during a test is strongly related to the type of excitation
and to the acquisition system. Indeed, some system (e.g., laser transducers) needs an
accurate pointing and so, a rigid support to maintain the tested structure. So, this choice
has to be made in compliance with the other requirements of the test.
In our case, the test was realized in "free-free" boundary conditions. This particular
conguration was chosen in order to avoid the apparition of additional unknowns concerning
the xing method. In addition, it gives rigid body modes at low frequencies, which
allow to distinguish them from the real modes of the OBC 2 card. To simulate these conditions,
the card was suspended by four elastics attached to the four endless screws' holes
of the card.
Type of excitation
Then, the type of excitation that will be used, must be dened. The selection criteria
are generally: simplicity and reliability.
In our case, the hammer excitation was chosen. Indeed, owing to the restricted dimensions
of the electronic card, this type of excitation is the most practical one. The
hammer used is the smallest available in the laboratory. It was equipped with a tip made
of vinyl, which allow to obtain an acceptable Power Spectral Density (PSD) in the range
of: [0 − 2000 Hz]. A better choice, with regard to the PSD, is to use the stainless steel
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