Sphere of Influence

In astrodynamics, a sphere of influence is the roughly spheroid-shaped region around a celestial body where that body's gravity is the dominant force acting on an orbiting or passing object. Mission designers use the boundary between two bodies' spheres of influence in the patched conic approximation, a simplified method for planning interplanetary trajectories that switches which body's gravity governs the spacecraft's motion at each boundary crossing rather than solving the full multi-body problem.