Abstract: An ion thruster has a source of a plasma, and an ion-optics system located in sufficient proximity to the source of the plasma to extract ions therefrom. The ion-optics system includes at least two grids arranged in a facing-but-spaced-apart relationship to each other, with each grid being axisymmetric about a grid axis. Each grid includes a peripheral region defining a grid plane perpendicular to the grid axis, a first region of curvature adjacent to the peripheral region, and a second region of curvature along the grid axis such that the first region of curvature lies between the second region of curvature and the peripheral region. The first region of curvature is a convexly curved segment of a first sphere relative to the grid plane, and the second region of curvature is a concavely curved segment of a second sphere relative to the grid plane.