VIBRATION TESTING OF THE Eu:CROPIS SATELLITE TEST STRUCTURE

Abstract

In the DLR (German Aerospace Center) compact satellite program the life supporting experiment Eu:CROPIS is developed. It is a small satellite weighing slightly more than 200kg. The proposed launch option is the Falcon 9 using the CASA adapter where it is placed on a balcony like support structure. The Eu:CROPIS satellite is being designed, produced and tested by DLR. Structural test for qualification are static and random loads, the random loads being the most demanding test. The static loads are tested using a sine burst test. As the structural test model is a prototype and as the project does not provide much time to repeat tests, the test sequence has been carefully chosen so as to limit structural damages before the end of the test campaign. Thus as many tests as possible are performed before the most demanding tests. Loads, stresses and deformations have been simulated by FEM-analyses before the tests. Still there are some uncertainties in the simulation due to the predicted damping and due to assumptions made to reduce the size and complexity of the model. Especially the random loads transfer into structural strain responses is very sensitive to the dynamic behavior. Therefore it is of interest to compare the assumed finite element structural response to the real measured one. For this purpose the test structure has been equipped with strain gauges to measure the peak strains in the primary structural parts in addition to the usual acceleration sensors. In this paper the test philosophy is explained using the prediction of structural stresses to sort the tests by intensity and thus by potential damage done to the tested structure. The measured natural frequencies, acceleration loads and internal strains are compared to the predicted ones. Reasons for deviations are given. The last test run showed significant changes in some acceleration responses. The search for the cause by analyses of the different acceleration responses is described.