Development of a dynamical model of a release mechanism for in-flight performance prediction

Abstract

LISA Pathfinder (LPF) was an ESA mission which was launched to test the most relevant technologies for the forthcoming mission, named LISA, which will be the first gravitational wave observer in space. The LPF payload includes two gravitational reference sensors, each one containing the sensing body of the experiment, i.e. a cubic-shaped test-mass (TM). The mission successfully fulfilled the requirements on the maximum noise level affecting the relative acceleration between the TMs. However, the mechanism which was responsible to inject them into free-fall condition presented some criticalities: the telemetry data showed an out-of-nominal TM state at the release, which may be explained with unexpected impacts between the TM and the release mechanism (GPRM) end effector. Experimental tests are performed on-ground to confirm this hypothesis and to provide an interpretation of the possible causes of the impacts. A 3D lumped-parameters multi-body numerical model of the mechanism is developed to extend the analyses results and a classifier is employed to distinguish between pre-release conditions in which impacts may occur or not. The analyses here presented give important guidelines for the design of the GPRM units for LISA.