Spacecraft Dynamic Behaviour In MicrogravityConditions

Abstract

Spacecraft dynamic behaviour is an important parameter in microgravity research experiments. Experiments and specimens must not be exposed to structural vibrations. Traditional design methods of spacecraft for dynamic environments mainly rely on finite element models. Validation of these models is done through comparison of modal parameters that are measured in an experiment on ground, in Ig gravity conditions. Real spacecraft dynamic behaviour in microgravity conditions is supposed to equal behaviour in gravity conditions. It is unknown whether conventional finite element models truly represent microgravity conditions. This research is a follow-on to experiments that were performed on ESA mission D-2. Structural vibration experiments are carried out by astronauts hitting the Spacelab structure with a hammer. Due to structural complexity of Spacelab, results of this experiment are not quite well suited for correct interpretation. This paper discusses another simplified investigation on dynamic behaviour in microgravity conditions. This research is done in th framework of an ESA/PRODEX project. A test structure is defined that is representative for real spacecraft components. Different types of materialsand different types of connections are used. Experimental modal analysis is performed in Ig gravity and in microgravity conditions. Microgravity research will be done in parabolic flight with a research aircraft. Finite element models are built for each of both conditions, for all different types of structures. Global Transactions on the Built Environment vol 19, © 1996 WIT Press, www.witpress.com, ISSN 1743-3509 458 Structures in Space conclusions compare structural behaviour in both conditions. Guidelines for appropriate finite element modelling will be derived.