Application of Steinberg vibration fatigue model for structural verification of space instruments

Dynamic phenomena in the design of new concepts of space systems

“…The first unit that was tested was the EPT-HET QM, where after passing the sine vibrations tests in each of the three orthogonal axes and the random vibrations tests in the lateral axes, it was not able to withstand the last random vibration test in the vertical axis (Z). By the functional tests and the visual inspections done after the vibration tests, it was found that the pins and electrical connections of some electronic components were irremediably broken, provoking the malfunction of the operations of the unit [48,49]. This fact motivated the in-depth investigation about the causes of the failures, which influenced the decisions taken later about the structural design and verification strategy.…”

“…Due to the problem of the QM, the verification strategy was redefined to a proto-flight approach, where the qualification and acceptance objectives should be reached in the same test campaign (proto-flight tests) performed on the FMs, which became the proto-flight models (PFM). These actions were decisive to successfully pass the proto-flight vibration tests [48,49].…”

“…STM and QM are more adequate for shock tests, so that it was decided in this project to perform the shock tests on the STEP QM. The EPT-HET QM was inoperative due to the severe failures found after the random vibrations tests [48,49], where the pins of the most susceptible electronic components broke due to the high deflections of the PCBs generated as a consequence of the resonance of their main modes. With the lessons learned after this event, the shock tests were carefully planned to avoid the same type of failures on the STEP QM.…”

“…The random specifications for the proto-flight tests in Z-axis for EPD units is shown in Figure 2-43 [48,49]. The duration of the proto flight random vibration test for each axis was 60 seconds.…”

“…The natural frequencies of the PCBs were calculated by FEM analysis, because the experimental determination of these modes could not be measured directly during the vibration tests due to the impossibility of locating accelerometers inside the units. As the functional performance of STEP and EPT-HET units after the proto-flight random vibration tests was successful [48,49], the shock verification can be justified if the shock specification is less severe than the random vibration tested levels at the frequencies of the fundamental modes of the PCBs. Different equations are proposed in [2] to define the equivalent response spectrum of the random vibration load with respect to the structural effect.…”