Toward a Space-based Gravitational Wave Observatory

NASA and ESA have explored a gravitational wave mission since 1993. In November 2013, the European Space Agency (ESA) selected the science theme, the ``Gravitational Universe,'' for its third large mission opportunity, known as `L3,' under its Cosmic Vision Programme. The planned launch date is 2034.~ NASA is seeking a role as an international partner in L3. NASA is supporting: (1) US participation in early mission studies, (2) US technology development, (3) pre-decadal preparations, (4) ESA's LISA Pathfinder mission and (5) the ST7 Disturbance Reduction System project. This talk summarizes NASA's preparations for a future gravitational-wave mission.