[Objective]This study focuses on reentry bodies that utilize momentum wheels as their actuation mechanisms,with a specific emphasis on addressing torque control deficiencies in the context of reentry-body attitude control.While concurrently preserving the symmetry of the reentry body,we propose a novel momentum-wheel layout that enhances the maximum torque output in the yaw,pitch,and roll channels.Additionally,a control scheme is introduced for the designed momentum wheel-based reentry-body system with the aim of achieving both the stability in attitude during reentry and agile attitude maneuvers.[Methods]In addressing the issue of insufficient torque output in momentum wheel-based reentry bodies,this paper introduces a symmetric layout for momentum wheels to improve the balance and maximize the torque output in individual channels.Due to the leverage of Lagrange's second-kind equations,a dynamic model for the attitude dynamics of the momentum wheel reentry body is developed.The study employs sliding mode control theory for tracking and controlling the attitude of the reentry body.For the purpose of mitigating the chattering issue associated with the sliding mode controller,a low-pass filter is incorporated with the controller to enhance system damping.Mathematical modeling is applied to characterize the reentry body with the added low-pass filter.Subsequently,in the presence of uncertain parameters and external disturbances that challenge precise estimation,we introduce a disturbance observer to compensate for uncertainties and enhance the robustness of the controller.Finally,an integral sliding mode control law is devised,and an input saturation compensation signal is introduced within the sliding mode control to reduce the impact of input saturation on the system.[Results]In this study,we employ both MATLAB simulations and a reentry-body simulation experimental platform to validate the effectiveness of the proposed momentum wheel layout,the designed controller,and the input saturation compensation strategy.Initially,during extensive maneuvering control simulations,a comparison of the maximum torque outputs for different momentum wheel layouts reveals a 60％decrease in the maximum torque output provided by the novel momentum layout proposed in this paper,compared to the traditional orthogonal layout.Subsequently,to validate the effectiveness of the designed controller,we rely on simulation examples to demonstrate the rapid and stable achievement of the desired trajectory by the reentry body.The yaw angle stabilizes within 4 s,with tracking errors in yaw and pitch angles stabilizing below 0.07°.In trajectory tracking experiments on the reentry-body experimental platform,the designed controller exhibits faster adjustment times and smaller overshoot in comparison to the traditional sliding mode controller.The spectral analysis indicates a 44.57％reduction in the maximum spectral amplitude at a stable state compared to the traditional sliding mode controller,and reaches 46.83 dB.Under parameter variations in the controlled object,the reentry-body simulation platform under the control of the traditional sliding mode controller exhibits pronounced oscillations during the balance process.In contrast,the designed controller,which incorporates filters and disturbance observers,effectively alleviates the burden on brushless motors,resulting in smoother attitude tracking curves and reduced system jitters.Finally,in the simulation verifying the effectiveness of input saturation compensation,the controller without input saturation compensation leads to significant oscillations and even instability.The introduction of input saturation compensation allows the control input to exit the saturated state more quickly,thus demonstrating the efficacy of the compensation strategy.[Conclusions]These foregoing outcomes emphasize that the suggested momentum wheel configuration,capitalizing on inter-wheel coupling,effectively mitigates the output pressures in the pitch and yaw channels.Not only do they optimize the utilization of momentum wheels but also they amplify the maximum torque output in the yaw,pitch,and roll channels.Furthermore,in contrast to conventional sliding mode control,the control strategy devised for the momentum-wheel reentry system in this study demonstrates superior performance.The approach manifests benefits including reduced vibrations,comparatively diminished overshoot,and heightened robustness.These results validate that the proposed momentum-wheel layout and control methodology perform both feasibly and efficaciously for the dynamic analysis and attitude robust control in reentry bodies,particularly in the presence of uncertainties.
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