We propose a robust control method for vehicle platoons based on a unified spacing policy, which can be customized for different vehicles within the platoon. This spacing policy integrates the constant time headway (CTH) and constant spacing (CS) policies into a single framework with some modifications. The policy can be adjusted to resemble either a CTH-like or CS-like approach by simply tuning a weighting factor for each vehicle. To increase road throughput, the velocity difference between the current vehicle’s velocity and the preceding vehicle’s low-pass filtered velocity is introduced to the proposed policy. A second-order low-pass filter is used for the preceding vehicle’s velocity. As a result, the sliding variable for each vehicle’s spacing error only requires the current vehicle’s position, velocity, acceleration, and the preceding vehicle’s position and velocity, all of which can be measured by onboard sensors. This design reduces the platoon’s reliance on inter-vehicle communication. A predefined-time modification is introduced to eliminate nonzero initial conditions in spacing and velocity errors, thereby improving transient performance. The local controller for each vehicle is based on a third-order nonlinear system model that accounts for nonlinear disturbances and engine lag. A smoothed sliding mode robust controller is then designed for each vehicle to stabilize its spacing error. The input-to-state stability (ISS) property of the spacing error is established through rigorous theoretical analysis. Furthermore, we demonstrate the practical strong frequency domain string stability (PSFSS) of the entire vehicle platoon, focusing on signal oscillations along the platoon. Finally, extensive numerical studies are conducted to demonstrate the effectiveness of the proposed method.

Robotic mobility in microgravity is necessary to expand human utilization and exploration of outer space. Bio-inspired multi-legged robots are a possible solution for safe and precise locomotion. However, a dynamic motion of a robot in microgravity can lead to failures due to gripper detachment caused by excessive motion reactions. We propose a novel Reaction-Aware Motion Planning (RAMP) to improve locomotion safety in microgravity, decreasing the risk of losing contact with the terrain surface by reducing the robot's momentum change. RAMP minimizes the swing momentum with a Low-Reaction Swing Trajectory (LRST) while distributing this momentum to the whole body, ensuring zero velocity for the supporting grippers and minimizing motion reactions. We verify the proposed approach with dynamic simulations indicating the capability of RAMP to generate a safe motion without detachment of the supporting grippers, resulting in the robot reaching its specified location. We further validate RAMP in experiments with an air-floating system, demonstrating a significant reduction in reaction forces and improved mobility in microgravity.