Control laws for an integrated power/attitude control system (IPACS) for a satellite using variable-speed singlegimbal control moment gyroscopes (VSCMGs) are introduced. Whereas the wheel spin rates of the conventional CMGs are constant, the VSCMGs are allowed to have variable speeds. Therefore, VSCMGs have extra degrees of freedom and can be used to achieve additional objectives, such as energy storage, as well as attitude control. We use VSCMGs in conjunction with an IPACS system. The gimbal rates of the VSCMGs are used to provide the reference-tracking torques, whereas the wheel accelerations are used for both attitude and power reference tracking. The latter objective is achieved by storing or releasing the kinetic energy in the wheels. The control algorithms perform both the attitude and power tracking goals simultaneously. A model-based control and an indirect adaptive control for a spacecraft with uncertain inertia properties are developed. Moreover, control laws for equalization of the wheel speeds are also proposed. Wheel speed equalization distributes evenly the kinetic energy among the wheels, minimizing the possibility of wheel speed saturation and the occurrence of zero-speed singularities. Finally, a numerical example for a satellite in a low Earth, near-polar orbit is provided to test the proposed IPACS algorithm.

Single-gimbal control moment gyros (CMGs) have many advantages over other actuators for attitude control of spacecraft. For instance, they act as torque amplifiers and, thus, are suitable for slew maneuvers. However, their use as torque actuators is hindered by the presence of singularities, that, when encountered, do not allow a CMG cluster to generate torques about arbitrary directions. One method to overcome this drawback is to use variable-speed single-gimbal control moment gyros (VSCMGs). Whereas the wheel speed of a conventional CMG is constant, VSCMGs are allowed to have variable wheel speed. Therefore, VSCMGs have extra degrees of freedom that can be used to achieve additional objectives, such as singularity avoidance and/or power tracking, as well as attitude control. The singularity problem of a VSCMGs cluster is studied in detail for the cases of attitude tracking, with and without a power tracking requirement. A null motion method to avoid singularities is presented, and a criterion is developed to determine the momentum region over which this method will successfully avoid singularities. This criterion can be used to size the wheels and develop appropriate momentum damping strategies tailored to the specific mission requirements.

Abstract-A novel adaptive control law for nonlinear Hamiltonian Multi-Input Multi-Output (MIMO) systems with uncertain parameters in the actuator modeling as well as the inertia and/or the Coriolis and centrifugal terms is developed. The physical properties of the Hamiltonian systems are effectively used in the control design and the stability analysis. The number of the parameter estimates is significantly lowered as compared to the conventional adaptive control methods. A smooth projection algorithm is applied to keep the parameter estimates inside a singularity-free region. The developed control scheme is applied for attitude control of a spacecraft with both the inertia and the actuator uncertainties.

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An adaptive control algorithm for the spacecraft attitude tracking problem when the spin axis directions and/or the gains of the flywheel actuators are uncertain is developed. A smooth projection algorithm is applied to keep the parameter estimates inside a singularityfree region and avoid parameter bursting. Numerical examples show that the controller successfully deals with unknown misalignments of the axis directions as well as the unknown gains of the flywheel actuators.

Complete attitude control of a spacecraft is not possible with only one single-gimbal variable-speed control moment gyro due to the conservation of angular momentum. However, partial attitude control without violating the angular momentum conservation principle is still possible. In this paper feedback controllers using only one singlegimbal variable-speed control moment gyro are presented that drive all three components of the angular velocity of a rigid spacecraft to zero, while at the same time a spacecraft body-axis points along an arbitrary inertial direction. To solve this problem, we first introduce a pair of angles to parametrize all feasible final spacecraft orientations at rest without violating the angular momentum constraint. Based on this parametrization, an LQR control law is designed to locally achieve the control objective. Afterwards, a multistage control law is proposed to achieve the same control objective for large initial conditions.

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