Human-Graded Rocket Stage Landing via Robotic Capture, Active Landing Legs, and Translating Hydraulic Platform

Dinesh Appavoo • 2026

Abstract

This paper presents a multi-layered hydraulic attenuation system designed for the controlled vertical landing of a crewed rocket second stage (Stage 2). The proposed architecture integrates three independently controlled, actively damped subsystems—a robotic catching arm assembly mounted on a vertical tower, hydraulic landing legs affixed to the rocket structure, and a translating hydraulic landing platform—to distribute the deceleration impulse over an extended distance and time interval. By coupling three active hydraulic stroke elements with a cumulative deceleration distance of d_arm + d_leg + d_pad, peak acceleration experienced by the crew is maintained within proposed human-graded limits, referenced against NASA's established crew tolerance criteria of 3g sustained and 6g transient loading. A physics-based analysis grounded in the impulse-momentum theorem demonstrates that translating the landing surface concurrently with the descending vehicle substantially reduces the net impulsive force compared to a static landing surface. A feedback control architecture employing hydraulic utilization monitoring governs the coordinated response of all three subsystems through three distinct operational phases: powered descent to arm capture, arm-guided descent to platform contact, and fully hydraulic deceleration to rest. The three-layer redundancy provides progressive safety margins and contingency capacity for off-nominal arrival conditions. System-level force balance equations, energy dissipation models, and control laws are derived using symbolic parameters and validated against human tolerance boundaries.