Microgravity environment dynamic disturbances

Abstract The microgravity environment on-board an Earth orbiting spacecraft provides various opportunities in utilization of experimental and application fields of fluid, materials and life sciences. The design of such spacecraft shall maintain a quality of the microgravity environment in terms of limit acceleration levels. The residual accelerations are specified in the time domain for frequencies below 0.1 Hz and in the frequency domain for frequencies between 0.1 and 1000 Hz. Gravity gradient, atmospheric drag and attitude stability control of the spacecraft rigid body will influence the time domain acceleration vectors. The frequency response between 0.1 and 1000 Hz is determined by various perturbation forcing functions of the spacecraft attitude control, equipment, payload and the crew and by interaction with the flexible spacecraft structure. Such a behaviour is called here the microgravity environment dynamics disturbances. It is the aim of the paper to describe a computational model for the prediction of the dynamic disturbances. This computational model will consist of three major elements. Each will stand for a response prediction in a dedicated frequency band with overlap between each other. The one model element will, by means of multi-body dynamics algorithm, describe the accelerated motions of the flexible spacecraft closed loop control. The second is a finite-element model for a broader low frequency structural dynamics calculation. The third one is the high frequency structure dynamics prediction model using test data from components and structure transfer functions. The outputs of the individual micro-g dynamic disturbance model elements are processed by a superposition program which result in an acceleration response spectrum over the frequency range 0.1–1000 Hz. The approach selected and the analytical and test methods are demonstrated. The computational model shall be applicable for spacecraft initial design studies and final verification tasks.