Simulation of a critical task of the LISA release mechanism: the injection of the Test Mass into geodesic

In LISA Pathfinder, the injection of the test mass (TM) into a geodesic or- bit represents a possible single-point failure of the whole mission. In this critical phase the Grabbing, Positioning and Release Mechanism (GPRM) releases the test mass from the caged condition to free-fall by means of a fast retraction of two opposite tips. A momentum transfer from the tips to the TM occurs due to adhesive bonds and possible asymmetry of the system. Since the electrostatic control authority is limited, the re- leased TM may be captured only if its residual velocity after release is below 5 μm/s. A combined experimental-analytical strategy has been conceived to test this phase. The compliance of the resulting injection with the requirements is here presented and dis- cussed.