Analysis and interpretation of the in-flight dynamics of a critical space mechanism

Abstract

The study hereby presented develops a mechatronic model of a critical space mechanism for a comprehensive interpretation of its in-flight performance. The mechanism was operated in the LISA Pathfinder European Space Agency mission, which was flown to test key technologies developed for detecting gravitational waves from space. The mission accomplished its scientific goal, i.e. demonstrating that the noise level affecting the relative acceleration between two test masses is within the requirements. Even though LISA Pathfinder was a successful mission, some criticalities had to be overcome. The mechanism responsible for releasing the test masses into free-fall caused the masses to assume unexpected velocities. Preliminary analyses, based on a mixed experimental-analytical approach relying on planar dynamic models, demonstrated that the velocities could be explained by impacts between the test masses and the mechanism end-effectors. Starting from the results of these analyses, the study hereby presented develops a fully 3D electro-mechanical lumped-parameter model of the mechanism, following a completely analytical approach. The model, which is validated through an extensive experimental campaign, benefits from a coupled dynamics between the two critical planes and aims at a comprehensive description of the mechanism performance. The signal processing technique adopted to estimate the model parameters is based on a regression algorithm, simultaneously applied to multiple signals of the mechanism dynamic response. Then, a mathematical model of the test masses and of its impactive interactions with the mechanism end-effectors is developed to perform a full description of the in-flight dynamics of the release phase. The test mass telemetry signals are processed to estimate its state at the in-flight releases and compared with the prediction of the validated model, highlighting accordance with the in-flight data and giving a reliable interpretation of the anomalies in the test masses state.