Prediction of the LISA-Pathfinder release mechanism in-flight performance

In the LISA Pathfinder mission, the grabbing positioning and release mechanism will perform a critical phase, which is the injection of a test mass into a perfect free-fall condition (also called geodesic trajectory). A possible failure is the test mass remaining adhered to the mechanism or released with an excessive velocity, which would hinder the subsequent capacitive control to the desired geodesic status. In space engineering it is recognized that mechanisms constitute critical subsystems, because they may have single point failures which can seriously affect the mission. In order to limit the risk, a good practice is to test the mechanism critical phases in an environment which simulates the conditions that will be experienced in operation. In the LISA Pathfinder ground testing plan a combined experimental-analytical strategy has been conceived to test this critical phase. The momentum transfer from an actuator to an adhered test mass upon quick separation is measured by means of a dedicated experiment, characterizing the behavior of adhesion under dynamic failure. In parallel, a mathematical model of the release mechanism electro-mechanical dynamics is experimentally validated. The mathematical model of the test mass in-flight injection into geodesic is built, combining the adhesion model with the identified model of the release mechanism. The compliance of the resulting injection with the requirements is presented and discussed. © 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.