Micro-vibration on board a spacecraft is an important issue that affects payloads requiring high pointing accuracy. Although isolators have been extensively studied and implemented to tackle this issue, their application is far from being ideal due to the several drawbacks that they present, such as limited low-frequency attenuation for passive systems or high power consumption and reliability issues for active systems. In the present study, a novel 2-collinear-DoF strut with embedded electromagnetic shunt dampers (EMSD) is modelled, analysed and the concept is physically tested. The combination of high-inductance components and negative-resistance circuits is used in the two shunt circuits to improve the EMSD micro-vibration mitigation and to achieve an overall strut damping performance that is characterised by the elimination of the resonance peaks and a remarkable FRF final decay rate of ?80 dB dec?1. The EMSD operates without requiring any control algorithm and can be comfortably integrated on a satellite due to the low power required, the simplified electronics and the small mass. This work demonstrates, both analytically and experimentally, that the proposed strut is capable of producing better isolation performance than other well-established damping solutions over the whole temperature range of interest.
Disturbances generated by reaction wheels on board the
spacecraft are among the most
. 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
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
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 num
ber of wheels.
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.
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.
Dynamic variability in nominally identical structures is an issue widely studied in structural dynamics community. Small uncertainties and manufacturing tolerances can significantly affect the dynamic behaviour of spacecraft payload. The aim of this paper is the investigation of such dynamic variability generated from both mechanical actuators and spacecraft structure itself. Both aspects will be tackled in this paper, suggesting two distinct approaches able to take into account these variations. First, vibration sources will be analysed by using real space mechanisms data (i.e. reaction wheels) and applying the proposed methodology in different cases. Finally, spacecraft structure variability will be addressed by looking at the dynamic behaviour of the satellite from a subsystem point of view. Such dynamic variability will then be assessed by the definition of specific margin of uncertainty.