Marcello Remedia

Dynamic Mass of a Reaction Wheel Including Gyroscopic Effects: An Experimental Approach

In recent years, driven by the increasingly stringent stability requirements imposed by some satellites’ payloads (e.g., the new generation of optical instruments), the issue of accurate onboard spacecraft microvibration modeling has attracted significant interest from engineers and scientists. This paper investigates the microvibration-induced phenomenon on a cantilever-configured reaction wheel assembly including sub- and higher harmonic amplifications due to modal resonances and broadband noise. A mathematical model of the reaction wheel assembly is developed and validated against experimental test results. The model is capable of representing each configuration in which the reaction wheel assembly will operate, whether it is hard mounted on a dynamometric platform or suspended free–free. The outcomes of this analysis are used to establish a novel methodology to retrieve the dynamic mass of the reaction wheel assembly in its operative range of speeds. An alternative measurement procedure has been devel...

A general methodology for analysis of structure-borne micro-vibration

Driven by the increasingly stringent stability requirement of some modern payloads (e.g. the new generations of optical instruments) the issue of accurate spacecraft micro-vibration modelling has grown of importance. This article focuses on the dynamic coupling between a source of micro-vibration (e.g. reaction wheel) and a structure, taking into account the uncertainties related to both parts. In this context, an alternative to the Monte Carlo Simulation for complex structures has been developed, consisting in sub-structural approach to perturb the natural frequencies of specific subsystem reduced with the Craig-Bampton method. In order to prove the validity of the method and its application to the theory of the coupling, benchmark examples and practical applications will be described.

Study of Correlation Criteria for Spacecraft-Launch Vehicle Coupled Loads Analysis

In spacecraft structural verification, Coupled Loads Analyses (CLAs) use Finite Element Models (FEMs) of the spacecraft and launch vehicle to predict flight loads. It is therefore essential that the spacecraft FEMs to be used in these CLAs are first validated through comparison with test measured data. This study has been conducted in order to assess the metrics/criteria used to quantify the level of correlation between the analytical model and physical spacecraft test structure. To explore this, both baseline spacecraft FEM and altered versions (generated by introducing errors to the baseline) have been subjected to the same loading scenarios. Differences in response between the baseline and ‘perturbed’ models have been observed. Various correlation criteria, such as modal assurance criteria and cross-orthogonality checks, and a lesser-known comparison of base forces, have been applied to quantify the level of correlation between each altered model and its corresponding baseline FEM. The results indicate that the more popular modal vector correlation methods may not be the most effective at predicting the level of error in peak displacement responses, and that the base force criteria, known as BFAC, may be more sensitive to changes in these responses.