It is believed that in order to accelerate a spacecraft to high, even sub-light, speeds, significant reserves of fuel are required. However, the limited speed of gravity propagation leads to the emergence of a relativistic effect of gravitational self-acceleration, when an extended object increases the speed of its movement without applying an external force to it, the so-called unsupported movement. Spacecraft engine on the effect of gravitational self-acceleration It is believed that significant reserves of fuel are required to accelerate a spacecraft to high speeds, up to subluminal speeds. However, the limited speed of propagation of gravity leads to the emergence of the relativistic effect of gravitational self-acceleration, when an extended object increases the speed of its motion without the application of an external force to it, the so-called unsupported motion. Conversely, gravitational some acceleration becomes impossible if the speed of propagation of gravity is infinite.