# Integrated Magnetic Management of Stored Angular Momentum in Autonomous Attitude Control Systems
###### Abstract
The continuous control of the stored momentum level enables spacecraft missions without the need for dedicated momentum dumping phases, increasing the system autonomy and facilitating complex and prolonged space operations to be carried out without constant ground support. Without loss of generality, the study focused on spacecraft with reaction wheels as the primary actuation system. Concerning the secondary actuators for angular momentum dumping, the spacecraft is considered to be equipped with magnetic torquers or magnetorquers. Despite the proposed method being theoretically applicable to satellites with thrusters, the low throttleability, the fuel consumption, and the spurious forces on the center of mass make them unsuitable for the proposed integrated application. Moreover, magnetic management of stored angular momentum can be easily applied to a broader group of spacecraft, from nano-satellites to very large space systems, and the magnetic momentum dumping is well established and effective in current spacecraft technologies [1]. Spacecraft attitude control has been known and studied since the early ages of space exploration. Indeed, despite the first few spacecraft only being launched into ballistic trajectories with uncontrolled or passively stabilized rotational motion, in 1959, the unmanned Luna-3 Soviet space probe had the world's first three-axis attitude control system to be activated while taking photos of the far side of the Moon [2]: spacecraft attitude dynamics are too fast or too complicated to be manually controlled, either from ground or onboard. Thus, vast literature on spacecraft attitude control systems is available and well consolidated [3; 4; 5], especially when angular momentum exchange actuators are used [6; 7; 8; 9]. Researchers have addressed the magnetic attitude control of spacecraft in low-Earth orbits (LEOs) since the late 1970s. [PERSON] and [PERSON] [10] set a milestone in this field, defining a method based on the use of averaged models that is extremely efficient in stabilizing the attitude of momentum-biased spacecraft. This work highlighted the excellent properties of magnetic attitude control in generating a dissipative action. In fact, it has been extensively and effectively applied for initial spacecraft angular rate dissipation (i.e., detumbling) or nutation damping. These applications have been deeply studied by numerous scientists [11; 12; 13; 14], and they have been successfully applied in real operative missions [15; 16]. Moreover, in recent years, with the advent of small satellite platforms and cubesats, the usage of magnetic attitude control has become even more frequent and interesting for the scientific community [17; 18; 19; 20; 21]. Among all these studies, the application of magnetic torques for angular momentum dumping was studied by [PERSON] and [PERSON] [22]; then, it was applied to a specific mission scenario [23; 24]. The problem of integrating the momentum dumping with attitude control was studied by [PERSON] [1], who proposed a controller based on periodic \(LQ\) and \(H_{\infty}\) to improve the classical cross-product control law [22] when applied to a zero-momentum inertially pointing spacecraft. Later, [PERSON] et al. [25] studied a static input allocation controller for reaction wheels' desaturation using magnetorquers. This study departs from the latter two contributions dealing with integrated magnetic momentum management and attitude control of Earth-orbiting spacecraft, and it proposes a different approach that integrates the classical cross-product control law with a proportional-integrative-derivative (PID) three-axis attitude control law. The method can be applied to nadir-pointing spacecraft and to inertially fixed platforms, but it can be easily generalized for any other pointing scenario. The system design and implementation are intended for autonomous spacecraft, which can be operated without significant ground support.