- This paper presents an approach to spacing vehicles along an arbitrary path. Previous research by the authors has shown the development of formation control laws assuming constant distances between vehicles as viewed by inertial observers. However, that approach is not advantageous for spacing vehicles along an arbitrary reference trajectory. By defining along-path and perpendicular-to-path spacing errors, ideal trajectories can be found for each vehicle in the formation. A sliding-mode control law is used to track the ideal trajectories, which provides better performance than a simpler control form. Simulation results demonstrate feasibility of the approach for a five-vehicle formation. Copyright 2010 by MITRE.