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This paper addresses the problem of powered descent control of a lunar lander during its final landing phase, where soft and precise landing at the target cite is required. In the literature, this problem has been solved considering a fully actuated lunar lander. Recently, landers are designed as complex systems with several onboard payloads and subsystems for completing demanding mission tasks. There are increasing constraints on mass budget and space availability onboard a lander. In order to meet these requirements, a novel controller using a single thruster is proposed. The proposed controller has three control inputs (thrust and two gimbaled angles) to control the six degrees of motion of a lander; these control inputs are non-affine. The proposed controller is designed based on variable structure control technique augmented with a high order filter, an immersion and invariance-based mass estimator and a sliding mode angular velocity observer. The stability analysis using Lyapunov theory and the results of the numerical simulations along with Monte Carlo simulations of the system show that the precise landing of the lunar lander using a single thruster is feasible. • The position and attitude control of a lunar lander using a single thruster is examined. • A novel controller along with lander mass and angular velocity observers are designed. • The proposed controller is based on variable structure control technique. • The Lyapunov theory is applied to prove the stability of the proposed control scheme. • Results of numerical simulations show the feasibility of the proposed control scheme. [ABSTRACT FROM AUTHOR]

To overcome the singularity problem of control moment gyros (CMGs) and simultaneously provide a lightweight, agile, and simple dynamical system, a CMG system called a double-gimbal scissored-pair control moment gyro (DGSPCMG) was recently proposed. The DGSPCMG is a hybrid mechanism that combines scissored-pair CMGs and a double-gimbal mechanism; further, the outer singularities in this system (saturation singularities) can be escaped by steering the scissored-pair gimbals. This system generates less perturbation torque and has almost no inner singularities except at the origin and the line along the outer gimbal axis. This paper proposes model predictive control (MPC) based steering laws for the mentioned CMG system. The proposed MPC based steering laws can directly provide the optimal gimbal rate under the nonlinear constraints in real time without using the inverse of the CMG Jacobian matrix, and hence, the singularities do not have to be considered when determining the gimbal steering rate of this system. Three objective functions are considered in the steering law design: fast maneuver-weighted type, minimum control energy type, and a hybrid of these two types. The control performances of these three MPC-based steering laws are compared via numerical simulations. Results demonstrate that the hybrid type can achieve both a short rise time of the angular velocity at the initial stage of control, and smooth stabilization to the target attitude; moreover, its settling time and control effort is between those of the other two types. • Double-gimbal scissored-pair control-moment gyros (DGSPCMG) is considered. • Model-predictive control (MPC) based steering laws are designed for this system. • Fast maneuver, minimum control energy types, and hybrid of these two are considered. • Hybrid type achieved a short rise time of angular velocity and smooth stabilization. • As setting a long receding horizon length, the settling time was shortened. [ABSTRACT FROM AUTHOR]

Abstract Solar radiation torque has a great impact on Chinese new generation geostationary meteorological satellite FengYun-4 since its single winged solar array configuration. Daily accumulation in angular momentum stored in reaction wheels may increase about 30Nms, and should be unloaded via bipropellant thrusters during a daily 15-min housekeeping period. How to prevent zero-crossing and saturation of wheels, how to reduce the operation speed range of wheels, and how to ensure the service continuity if any one of wheels fails are the problems to be faced. In addition, both the uncertainty of thruster torque and the variability of solar radiation during all the life span may go against with the automaticity of angular momentum management. In this paper, a null-space-based momentum management method is presented, upon which the angular momentum is managed by null motion control while service and dumped during the housekeeping period. In-flight and numerical simulation results demonstrate the reliability and validity of this strategy. Highlights • The angular momentum management strategy for Fengyun-4 satellite is proposed. • The dumping target is set in three-dimensional space and null space respectively. • Each momentum wheel's rotation speed range is optimized. • Quick momentum self-adjusting is realized when the wheel configuration changes. • Auto-unloading logic is specified for the uncertainty of thrust and solar radiation. [ABSTRACT FROM AUTHOR]

Spacecraft attitude control solutions typically are torque-level algorithms that simultaneously control both the attitude and angular velocity tracking errors. In contrast, robotic control solutions are kinematic steering commands where rates are treated as the control variable, and a servo-tracking control subsystem is present to achieve the desired control rates. In this paper kinematic attitude steering controls are developed where an outer control loop establishes a desired angular response history to a tracking error, and an inner control loop tracks the commanded body angular rates. The overall stability relies on the separation principle of the inner and outer control loops which must have sufficiently different response time scales. The benefit is that the outer steering law response can be readily shaped to a desired behavior, such as limiting the approach angular velocity when a large tracking error is corrected. A Modified Rodrigues Parameters implementation is presented that smoothly saturates the speed response. A robust nonlinear body rate servo loop is developed which includes integral feedback. This approach provides a convenient modular framework that makes it simple to interchange outer and inner control loops to readily setup new control implementations. Numerical simulations illustrate the expected performance for an aggressive reorientation maneuver subject to an unknown external torque. [ABSTRACT FROM AUTHOR]

This paper considers the attitude and angular velocity stabilization problem of a class of flexible spacecraft under actuator complete failure. Firstly a new model simplification strategy is put forward to weaken the coupling effects. Then an adaptive observer-based estimation method is proposed to estimate the uncertainty of flexibility, based on which a feedback fault-tolerant control scheme is further developed which guarantees the system stability and asymptotic attitude converging properties. The simulation results illustrate the efficiency of the theoretical results. [ABSTRACT FROM AUTHOR]