arXiv subjects

Hancheol Cho

Publications and source records attributed to Hancheol Cho.

3 recordsLinked to original sources

arXiv2026

Variable-Step Time-Delay Control for Proactive Aperiodic Spacecraft Attitude Control

This paper addresses proactive aperiodic spacecraft attitude control under model uncertainty, environmental disturbances, and actuator degradation. To this end, we develop Variable step Time Delay Control (VTDC), which jointly designs robust feedback control and control-update scheduling rather than treating them as separate components. Inspired by adaptive stepsize regulation in Runge Kutta integration, VTDC structures the local control error to scale with the realized timestep. Using sliding manifold based Time Delay Control, the resulting System Time Delay Error (TDE), which reflects local model and uncertainty variations, is shown to be quadratically bounded by the control interval. This relation yields a closed form feedback law that enlarges or reduces the subsequent interval to regulate the TDE magnitude. The next update time is therefore determined algebraically without continuous trigger monitoring, future state prediction, or iterative search. The resulting variable step closed loop admits bounded timesteps and step ratios, excludes Zeno behavior, and renders the sliding variable uniformly ultimately bounded. Nonlinear spacecraft attitude control simulations demonstrate accurate tracking with low scheduling cost under representative uncertainties and disturbances.

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arXiv2026

Estimated-State Adaptive Sliding Mode Control and Disturbance Observation Using Second-Order Surfaces for Spacecraft Formation Reconfiguration

This paper presents a two-phase relative orbit control framework for spacecraft formation flying that combines analytic energy-optimal transfer with robust adaptive sliding mode tracking. In the first phase, a chaser is transferred from an arbitrary initial relative state to a projected circular orbit (PCO) under the Clohessy--Wiltshire dynamics. Rather than selecting the PCO entry phase by numerical sweeping, the transfer cost is parameterized by the phase angle, and the stationarity condition is reduced to a quartic polynomial whose real roots yield all candidate entry phases. In the second phase, the chaser maintains the PCO in the presence of external disturbances. An adaptive sliding mode controller (ASMC) and a sliding mode disturbance observer (SMDO) are employed in both phases to provide robust tracking and disturbance compensation. The observer reduces the lumped disturbance to a bounded residual, while the controller updates its adaptive gain from an estimated-state second-order sliding variable. The second-order surface tightens the ultimate tracking error bound, and a practical derivative estimation method reuses available reference velocity and acceleration signals, avoiding finite-difference noise amplification and additional differentiator tuning. Simulations demonstrate accurate tracking, effective disturbance rejection, and a smooth transition between the two phases.

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arXiv2024

Adaptive Smooth Control via Nonsingular Fast Terminal Sliding Mode for Distributed Space Telescope Demonstration Mission by CubeSat Formation Flying

This paper presents a nonsingular fast terminal sliding mode-based adaptive smooth control methodology for a distributed space telescope demonstration mission. The distributed space telescope has a flexible focal length that corresponds to the relative position in the formation flying concept. The limited specification of a CubeSat generally restricts the performance of actuators, most critically the degrees of freedom of controlled motion. This investigation leads to the development of an adaptive smooth control methodology via nonsingular fast terminal sliding modes. The adaptive smooth control algorithm that was developed for a single-input single-output system is adopted and extended to the relative orbit and attitude control systems of the distributed space telescope. The software simulation is conducted under a real mission, which means the real CubeSat structures, hardware specifications, and operational constraints. The proposed algorithm possesses only seven parameters that can be easily adjusted considering their physical meanings. Furthermore, the pre-designated error bounds are analytically derived, which enhances the applicability of the algorithm to real missions. The simulation compares the efficiency of the adaptive smooth nonsingular fast terminal sliding mode controller with the linear quadratic regulator and proportional derivative algorithms. The results verify that the adaptive smooth nonsingular fast terminal sliding mode control algorithm shows better control performance in the perspective of the alignment time and the fuel consumption for the distributed space telescope demonstration mission.

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