Ground based tests for LISA and LISA Pathfinder

LISA (Laser Interferometer Space Antenna) will be the first space-born antenna for Gravitational Waves in the range 10^-4-10^-1 Hz. It is a joint ESA-NASA effort, and it consists of a constellation of three satellites in heliocentric orbit, forming two semi-independent Michelson interferometers. Each spacecraft contains two test masses, nominally in pure geodesic motion, without any mechanical contact with the spacecraft. Distances between test masses on board each couple of spacecrafts (5 million Km apart) are monitored using on board lasers. On-ground tests are required to understand the couplings between the test-mass and environment, and between the various degrees of freedom of the test-mass itself. A two soft DOF system, a double roto-translational pendulum, is being studied as a test bench. Here we present an analysis of the system behavior, and the study of an active control system for the test-mass.