The effects of random vibration on the dimensional stability of space-based precision structures

Abstract

Low-cost Earth-imaging instruments typically require high performance structures to ensure that critical alignments of optical components are maintained between the assembly phase, and the on-orbit operational phase. There are a number of threats to structural dimensional stability, including thermal cycling, moisture desorption and launch vibrations. This last area is the subject of this thesis. The main aim of the research described here is to better understand the effects of random vibration on the dimensional stability of precision structures. The first part of this research considered the degree to which random vibration is a problem - this was assessed by comparing its effects on dimensional stability with those of other typical environmental stressors. This was accomplished by performing a series of environmental tests on an optical breadboard structure, and measuring the dimensional stability throughout. These tests showed that random vibration could indeed pose a significant threat. The second part of the research aimed to better understand the dimensional stability response of specific structural elements - namely materials and bolted joints - to random vibration. This required the development of novel test setups and metrology techniques. Controlled tests were performed in both these structural areas, and a number of useful conclusions were drawn. The final part of the research was to investigate the empirical results using FEA methods. A significant challenge was to develop a modelling technique that is capable of predicting dimensional stability responses to random vibration. In the case of the material tests, the response of the test samples was correctly predicted using FEA with cyclic plasticity properties and parameters identified from static tests. This research has produced a number of relevant findings for spacebased stable optical bench structures. These have been condensed into a series of recommendations for design, analysis, testing, metrology and bedding-in vibration for future optical payload projects.

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