Implementation-Oriented Analysis of Sliding Mode Control for Vertical Landing Rockets with Actuator Feasibility Constraints

Vertical landing rockets (VLR) impose stringent demands on guidance systems, particularly during terminal descent. While numerous control strategies exist, many implicitly assume ideal actuator behavior, failing to reflect practical hardware realities. This paper presents an implementation-oriented analysis of common control architectures-Cascaded PID, Integral Sliding Mode Control (ISMC), and Super-Twisting ISMC (STA–ISMC)-subject to strict actuator feasibility constraints. Rather than proposing a new control law, the study investigates failure modes caused by thrust saturation, gimbal limits, delay, and sensor noise using a high-fidelity planar simulation. Results indicate that when feasibility limits are violated, the PID controller remains bounded and physically consistent. In contrast, ISMC and STA–ISMC may lead to hard landings or non-physical divergence due to integral windup and loss of effective control authority. As a central contribution, a minimal feasibility-aware supervisory layer is introduced. Operating independently of the control law, this supervisor prevents runaway behavior by freezing integral action and enforcing a passive response during infeasible conditions. The results highlight that in safety-critical landing systems, feasibility awareness and system architecture are as vital as controller robustness.