## 5 Discussion  
Models are widely used in different areas of spacecraft design, whereas simulation is a key element in supporting the engineering and operational activities of space systems. In this regard, System Modeling and Simulation (M&S) is considered a system-level support discipline. This discipline encompasses the simulation models and infrastructure to support specification, design, and the entire Verification and Validation (V&V) process. Given the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Simulation Approach** & **Angular Velocity Norm, Mean Value** &
\begin{tabular}{c} **Angular Velocity Norm,** \\ **Standard Deviation** \\ \end{tabular} \\ \hline SIL & 0.0022 & \(1.2858\times 10^{-4}\) \\ MIL & 0.0022 & \(1.3972\times 10^{-4}\) \\ PIL & 0.0022 & \(1.3705\times 10^{-4}\) \\ HIL & 0.0024 & \(1.4217\times 10^{-4}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Model-based performance results for Bdot (calculated after 2 orbits). Figure 21: Pointing error comparison: SIL vs MIL vs. PIL vs. HIL with nadir controller. Eclipse periods are highlighted in gray. Figure 20: Norm of the angular velocity of SIL, MIL, PIL, and HIL using Bdot. importance of maximizing the benefits of their use, the European Space Agency (ESA) has established a Technical Memorandum to cover the modeling and simulation facilities required to support all these system-level activities: ECSS-E-ST-10-21A. Standard \"Systems Engineering: System modelling and simulation\". In this research, this analysis is further explored, not only at the system level related to the space segment or ground segment, but also at the module and component level. This approach introduces early-stage testing for initial phases of development specifically for the ADCS module, specifying details on facilities and interfaces. During the development process, models are also supposed to mature in order to support system-engineering trade-offs. In the first stage of the project, as seen in [25], a System Concept Simulator (SCS) was developed for fast evaluation and system design concepts since it was not running in real time. Nevertheless, this research went a step further into a Functional Engineering Simulator (FES) that allows us to verify critical elements of the baseline system proposed, reusing mathematical models of the SCS and adding details to it as seen in the MIL approach. Finally, these simulators prepared the basis for the Functional Validation Testbench (FVT) to support the analysis of the system performance and the V&V process of critical components as seen in SIL, PIL, and HIL. Additionally, this paper introduces a methodology based on V-cycle for project development at a module level for the ADCS. Since no uniform methodology is established in the ECSS-E-ST-10-21A for this level of development at early stages, this research complements a standard methodology for the design process that could be characterized by the designer's necessities based on the model-based design. Delving into the contribution of each simulation environment to the design and V&V process, this process started with the extension of the SCS previously developed. Detailed models of the space environment and also of the sensors and actuators were included in order to obtain more realistic results considering jitter, noise, and data handling between the space environment and the controller as seen in MIL. These models were included in all the simulation environments which allowed us to analyze not only the controller performance in each environment but also the effects of the embedded capabilities and computational resources in the performance of the controller. In this sense, it could be seen that the controller executed on board in real time never exceeded 24.06% of the memory capacity and 19.44% of the RAM capacity executed in PIL and HIL environments.