Gravity-induced contact with the Earth’s surface has been constant throughout the evolution of the human species, and human health depends on it. Providing “artificial gravity” and a firm contact surface to an interstellar crew is conceptually simple, due to the equivalence of gravitational and inertial mass. The physiological benefits of gravity are preserved through mechanical acceleration, which may be linear, centripetal, or some combination. Centripetal acceleration requires far less energy to maintain. Though it provides a distorted gravitational experience when the rotational radius is small, the minimum size of an interstellar spacecraft will almost certainly derive from the size of its population and other aspects of human life support, not from any dimensional limit for comfortable rotation. There must nevertheless be some linear acceleration if the spacecraft is ever to reach another star system. This may be either in-plane or on-axis relative to the centripetal. The optimal choice depends on the magnitude of the linear component relative to the centripetal.