Dr Salvatore De Lellis

Due to constantly increasing requirements for more precise and high-resolution instrumentations, microvibration prediction represents an issue of growing importance. Hence the need of reliable analysis tools which can evaluate microvibrations effects efficiently. This paper describes how to tackle the issue of structural uncertainties in microvibration predictions. In particular, uncertainties related to the microvibration sources are analysed as well as those linked to the modelling of the structure. A methodology to define the worst case of vibration produced by on board sources is presented and compared to experimental data. Additionally, an approach to quantify the uncertainties in the Finite Element model is also described.

Disturbances generated by reaction wheels on board the spacecraft are among the most substantial. Hence they play a crucial role when microvibration budget has to be assessed. This paper aims at characterising the effects of RW on the structure by focusing on the format of the disturbance input matrix of these components. In particular the case of single and multiple wheel accounted for. In the first one the responses are evaluated at some specific locations of the reaction wheel where their disturbance is amplified, i.e. harmonics. In the second case a more realistic scenario is considered with several wheels to be characterised and the effects of neglecting some terms of the disturbance input matrix are discussed. Finally a sensitivity analysis is carried out to quantify in which extent changes in the input matrix can alter the response. A preliminary methodology is then suggested to characterise a large number of wheels.

It is well documented that reaction wheels are among the most significant microvibration sources in space applications. These components, despite being nominally identical, can show differences in the generated signals due to manufacturing imperfections in their internal elements, such as ball bearing, internal and external race. In this article a methodology to account for those variations in microvibration predictions is proposed, aiming at generating a disturbance input matrix that encompasses the effects of a family of reaction wheels. With such a tool, it is possible to provide a more accurate microvibration budget at an early stage of the mission, reducing the uncertainty margin usually applied to quantify reaction wheel effects on the structure. As a consequence better designs are produced faster and cheaper. This allows for more flexibility in the mission design and reduces the degree of uncertainties in the predictions. Furthermore, it is shown that the proposed approach is able to characterise the effects of the entire family of wheels by considering only a limited number. The methodology is validated by assessing the microvibration excitation on different structures, including a real space structure with various reaction wheel mounting configurations.