Deployment repeatability in mechanically jointed precision structures.

摘要

Launch vehicle dimensions are critical for space structures. If an operational structure is larger than the volume of its launch vehicle, that structure must be segmented, and deployed on-orbit. Despite previous successful deployments of space structures, deploying telescope mirrors on-orbit is still seen as a high-risk operation, due to our current inability to predict the passive shape of the deployed structure to the high level of precision that telescope mirrors require. Thus, examining deployment repeatability is important for space telescope structures.; Experimental results obtained in a ground laboratory with a precision deployable test article and presented in this thesis show that the level of repeatability in a structural deployment can be correlated with the performance of that structure's mechanical joints. Further, the experiments demonstrate that joints designed with high linearity (and therefore good post-deployment stability) are not necessarily highly repeatable. These experimental results raise the question of what criteria should be used to design joints for good repeatability.; The sources of poor repeatability in a mechanical joint are identified as being either geometrical or mechanical uncertainties. Repeatability will be dependent on both the size of the uncertainties and the size of the sensitivity of the repeatability to those uncertainties. Geometrical uncertainties can be addressed through careful manufacturing and material choice. However, the size of the mechanical uncertainty (the uncertainty due to force applied across a mechanism) has a much more subtle impact on mechanism design. In this thesis, the sensitivity of the mechanical uncertainty is examined closely. The frictional forces at the mechanism interfaces are bounded in order to predict the repeatability of a mechanism successfully. Bounding the displacement due to friction in the microslip or pre-Coulombic regime is possible using the width of the hysteresis. The sensitivity of the mechanism to applied preload and to frictional forces is examined for a series of Hertzian contact test cases. The test cases show that redundancy can play a role in reducing preload sensitivity.; The thesis concludes with a set of design rules that can be used to design more repeatable mechanisms, which will lead to predictable passive shapes for deployed structures.