Gravitational compensation for the LISA pathfinder

This paper addresses the problem of compensating self-gravity for the LISA Technology Package. Massive components onboard the spacecraft produce a gravitational imbalance on the free-falling test masses. We present here a compensation scheme to reduce the gravitational forces, torques, stiffness and cross-talk to values within requirements. Gravitational analysis and subsequent compensation are needed to limit the gravitational imbalances in order to reduce the force noise and force gradients associated with the electrostatic actuation that must compensate any residual gravitational imbalances. Starting from an educated guess based on simple Newtonian arguments, we present the approximate shapes of a compensation block solution which minimizes the residual gravitational imbalance and stiffness while adding a minimum of mass.