Planetary bodies characterized by low gravitational acceleration, such as the Moon and near-Earth asteroids, impose unique locomotion constraints due to diminished contact forces and extended airborne intervals. Among traversal strategies, hopping locomotion offers high energy efficiency but is prone to mid-flight attitude instability caused by asymmetric thrust generation and uneven terrain interactions. This paper presents an underactuated bipedal hopping robot that employs an internal reaction wheel to regulate body posture during the ballistic flight phase. The system is modeled as a gyrostat, enabling analysis of the dynamic coupling between torso rotation and reaction wheel momentum. The locomotion cycle comprises three phases: a leg-driven propulsive jump, mid-air attitude stabilization via an active momentum exchange controller, and a shock-absorbing landing. A reduced-order model is developed to capture the critical coupling between torso rotation and reaction wheel dynamics. The proposed framework is evaluated in MuJoCo-based simulations under lunar gravity conditions (g = 1.625 m/s^2). Results demonstrate that activation of the reaction wheel controller reduces peak mid-air angular deviation by more than 65% and constrains landing attitude error to within 3.5 degrees at touchdown. Additionally, actuator saturation per hop cycle is reduced, ensuring sufficient control authority. Overall, the approach significantly mitigates in-flight attitude excursions and enables consistent upright landings, providing a practical and control-efficient solution for locomotion on irregular extraterrestrial terrains.

翻译：以月球和近地小行星为代表的低重力天体，由于接触力减弱和空中滞留时间延长，对运动施加了独特的约束条件。在各种穿越策略中，跳跃运动具有高能效的优点，但易因推力生成不对称和地形交互不均匀而导致飞行中姿态失稳。本文提出了一种欠驱动双足跳跃机器人，该机器人采用内部反作用轮在弹道飞行阶段调节机体姿态。该系统被建模为一个陀螺体，从而能够分析躯干旋转与反作用轮动量之间的动态耦合。运动周期包含三个阶段：腿部驱动的推进跳跃、通过主动动量交换控制器实现的空中姿态稳定以及具有减震作用的着陆。本文建立了一个降阶模型，以捕捉躯干旋转与反作用轮动力学之间的关键耦合关系。所提出的框架在基于MuJoCo的仿真环境中，于月球重力条件（g = 1.625 m/s^2）下进行了评估。结果表明，激活反作用轮控制器可使飞行中峰值角偏差降低超过65%，并将着陆时的姿态误差限制在3.5度以内。此外，每个跳跃周期的执行器饱和程度得以降低，确保了充足的控制能力。总体而言，该方法显著减轻了飞行中的姿态偏移，实现了稳定的直立着陆，为在不规则地外地形上的运动提供了一种实用且控制高效的解决方案。