LISA Pathfinder was an ESA technology test mission for the eLISA/NGO mission to search for gravitational waves generated by massive objects such as black holes. NASA contributed one of two payloads, named ST-7.

LISA Pathfinder paved the way for eLISA/NGO. It tested new methods of spacecraft control and determined if laser interferometry is feasible at the level of accuracy required by eLISA/NGO.

LISA Pathfinder placed two test-masses in a nearly perfect gravitational free-fall, for controlling and measuring their motion with unprecedented accuracy. This was achieved through state-of-the-art technology comprising inertial sensors, a laser metrology system, a drag-free control system, and an ultra-precise micro-propulsion system.

All these technologies are essential not only for eLISA/NGO—they also lie at the heart of any future space-based test of Einstein's General Relativity. LISA Pathfinder was launched in 2015.

Final Launch Preparations for LISA Pathfinder: Images of Integration of LISA Pathfinder into VEGA rocket. Photo credit(s): ESA, Manuel Pedoussaut, 2015