## 5 Discussion  
The paper presented an attitude determination and control subsystem (ADCS) to align the solar arrays of a spacecraft to the Sun, exploiting only solar arrays and angular rates measurements with no information of the three-dimensional direction of the Sun. In fact, the system only exploits the Sun angle with respect to the unique solar arrays' normal direction to orient the solar cells. This ADCS control method is not designed to provide support to a nominal phase of a space system, but to guarantee a positive electric power generation even after multiple failures have occurred. The power consumption to support the control effort is largely satisfied by the produced power, which can be only generated if the spacecraft attitude is controlled. The end-to-end process to achieve the pointing of the solar arrays with the imposed limited measurements is new, conceived, and developed as presented in this research work. The proposed determination and control algorithms guarantee the acquisition of the Sun in front of the solar arrays and a stable Sun pointing. This has been proven by extensive numerical simulation campaigns, which have been briefly summarized in this paper. The numerical verification of the ADCS performance with momentum exchange actuation has been conducted according to the international verification standards. In this case, the proposed ADCS is fully capable to satisfy its design requirements. This can be applied to any actuation method that guarantees full controllability on at least two body axes orthogonal to the solar arrays normal. For example, similar results can be obtained by exploiting thrusters in pairs. Whenever full controllability is not continuously available along the prescribed axes, such as with magnetic actuators, the ADCS does not achieve a stable Sun pointing. However, it is capable to improve the electric power generation capacity with respect to a non-controlled system. Even this claim has been verified with numerical simulations, executed according to international standards. The implementation of the presented algorithms is computationally efficient, and it does not impose demanding requirements on the computational resources to be available onboard. Thus, any class of spacecraft may exploit these control methods. The inherent discrete-time formulation of the algorithms allows an easy implementation on hardware working at various sampling frequencies. The presented results are valid for an ADCS working at 10 Hz, with a sampling time of 0.1 s. Positive results have been achieved with a maximum sampling time up to 2 s. Future works can be directed to assess the performance of the proposed methods with other actuation technologies or to theoretically demonstrate the properties of the control modulation. Anyhow, it shall be noted that the proposed attitude determination and control algorithms for solar array pointing are based on proportional-derivative control schemes, and they preserve their peculiar closed-loop features.  
Figure 12: Solar arrays power Monte Carlo analysis, with no control action.  
**Author Contributions:** Conceptualization, A.C.; methodology, A.C.; software, A.C.; validation, A.C.; formal analysis, A.C.; writing--original draft preparation, A.C.; writing--review and editing, A.C.; funding acquisition, M.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.