ESA GNC Conference Papers Repository
In-orbit performance of the LiSA pathfinder drag free and attitude control system
LISA Pathfinder is a technology demonstrator mission that was funded by the European Space Agency and that was launched on December 3, 2015. LISA Pathfinder is currently conducting experiments to demonstrate key technologies for the future Gravitational Wave Observatory (GWO) in its operational orbit at the L1 Lagrange point of the Earth-Sun system. These key technologies include the two inertial sensors, the optical metrology system, a set of µ-propulsion cold gas thrusters and in particular the high performance Drag Free and Attitude Control System (DFACS) that controls the spacecraft in 15 degrees of freedom during its science phase. The main goal of the DFACS is to shield the two test masses inside the inertial sensors from all external disturbances in order to achieve a residual differential acceleration between the two test masses of less than 3·10-14 m/s2/vHz over the frequency bandwidth of 1 to 30 mHz. Thus, the performance of the DFACS has a direct impact on the scientific performance of the mission. This paper focuses on the DFACS that is currently in use on LISA Pathfinder and in particular on the drag free mode that is used for the main science mode of the spacecraft. The paper provides pre-flight predictions for the performance of the DFACS in science mode and compares these predictions to the performance that is currently achieved in-orbit. Some results are also discussed for the mode transitions up to science mode, but the focus of the paper is on the steady state performance of the main science mode. The paper shows the exceptional performance already achieved during commissioning, which not only met the commissioning requirements (relaxed by one order of magnitude), but also the science requirements with some margin. Based on the achieved results, some lessons learnt are formulated in order to extend the results to the drag free control system to be designed for the future GWO mission.