Test-mass release phase ground testing for the LISA pathfinder mission

Aim of the LISA Test-flight Package on board the LISA Pathfinder mission is to provide in-flight demonstration of some of the LISA critical technologies in achieving the free-fall condition of a LISA-like test-mass in the bandwidth from 1 to 30mHz. Accordingly, owing to high inertial loads arising during the launch phase the test-mass needs to be firmly secured to the GRS, in order to avoid collision with the surrounding electrodes and housing parts. After the launch and orbit commissioning, the test-mass must be released to floating conditions, in compliance with strict requirements of initial position and velocity, due to the low force and torque authority made available by the capacitive actuation system. The Caging Mechanism Assembly is being designed by Alcatel Alenia Space Italia and it constitutes the GRS subsystem dedicated to cage and release the test-mass. The release phase to floating conditions has been identified as critical for the entire mission, therefore a ground-based verification of such a function has been deemed necessary. The verification approach adopted is to set both test-mass and release-dedicated plunger mock-ups in representative tribological conditions of the in-flight situation. An effort is being made to build a facility that enables to characterize the momentum transfer between the two suspended bodies and verify the compliance of the design of the release-dedicated mechanism subsystem of the Grabbing Positioning and Release Mechanism of the CMA. The proposed experiment and the facility status are here presented and discussed. © 2006 American Institute of Physics.