A REALISTIC APPROACH IN THE PREDICTION OF THE ACES MICRO-GRAVITYENVIRONMENT

摘要

The Atomic Clock Ensemble in Space (ACES) is anensemble of two atomic clocks that will be installed onthe External Platform Facility (EPF) of Columbus. Thelocation closest to ACES for which a micro-gravityspecification existed was at the interface betweenColumbus and the EPF truss. This is approximately 1meter away from the ACES interface. Since the EPFtruss will both amplify and filter the accelerations, anestimation of the environment directly at the ACEScenter of gravity was required.The baseline approach to predict the micro-gravityenvironment of an ISS payload is based on a globalcoupled analysis at ISS level performed by NASA.When a modification is made for example to the stationor to disturbance sources, new environments are notreadily available. A new analysis involves a lengthyprocess due to the large model size and elaborated post-processing.A classical approach for any evolution, or in this case topredict the environment at a new location, is to performa local loop in a very conservative manner. In this typeof analysis the specified micro-gravity environment isapplied underneath the EPF truss. Responses can thenbe found at ACES. However the applied environment isan envelope and such an analysis predicts unrealisticallyhigh accelerations at several frequencies. Thepessimistic environment calculated in this way wasunacceptable for the fulfilment of the scientificobjectives.To obtain a more realistic environment a coupled modelof ACES and the Columbus was generated. Unitaccelerations were applied at the interface between thespace station and Columbus and responses (or transferfunctions) were extracted at EPF and at ACES. Scalingall accelerations such that those at EPF matched thespecified EPF environment, a better and acceptableapproximation of the ACES micro-gravity environmentwas established.