Artist's impression of LISA Pathfinder. LISA Pathfinder is an ESA spacecraft that was launched on December 3, 2015. LISA Pathfinder will test in flight the concept of low-frequency gravitational wave detection: it will put two test masses in a near-perfect gravitational free-fall, and control and measure their motion with unprecedented accuracy. To do this it will use inertial sensors, a laser metrology system, a drag-free control system and an ultra-precise micro-propulsion system. Release date November 14, 2015.