# Moon Sensor Station to Improve the Performance of Lunar Satellite Navigation Systems
## 7 Discussion and Conclusions  
Different solutions for a lunar local sensor were evaluated and compared. A new working principle was described for a local sensor (the ISL solution) and designed, proposing an initial version for the communication protocol. The simulation results show that there is an increase in navigation accuracy using a local sensor, with a significant improvement when the proposed ISL solution is exploited. Table 3 summarizes some final considerations. The proposed ISL performs as well as or even better than the DRS, providing a huge accuracy improvement for the vertical positioning error. For the horizontal error, the DRS performance can be further improved with the combined use of DRS+ISL. In terms of accuracy, in any case, the DRS+ISL configuration always provides the best performance. It is also important to consider that the DRS solution does not have important limitations in terms of coverage [23], and that the error reduction is huge even for a baseline of hundreds of kilometers. At the same time, the DRS does not improve the availability of the service. On the other hand, the ISL always enables the navigation service even without satellites in view. The table also reports the expected complexity and dimensions for the local sensor and the user device, considering the working principle and comments given in the previous sections. In particular, it must be recalled that the introduction of the ISL calls for additional room on the local sensor for the phased array antennas and additional complexity due to the need for AOA estimation. Moreover, the user side also requires a more complex device to interrogate the local sensor. This increases cost and can reduce the initial reliability compared to a more standard solution such as the DRS. It must be noted that other important parameters, such as power consumption, temperature management, lifetime, and environmental factors, such as lunar dust on the antennas and signal propagation, are not considered in this study and will likely be analyzed in future works. Moreover, the authors would like to emphasize that such challenges are likely common across all systems involved in the Artemis exploration era, which envisions a sustained human presence on the Moon, and it is expected that these issues will be addressed through dedicated studies beyond the scope of this work. Finally, although in the authors' opinion the proposed models are sufficient to provide an initial and reasonably accurate estimation of the expected performance, the introduction of time-correlated errors and non-Gaussian distributed models for the measurement errors could further enhance the statistical and mathematical frameworks used for system evaluation, leading to a more precise performance estimation. In conclusion, in the opinion of the authors, the exploitation of differential corrections can be an effective initial solution, delivering significant improvements with minimal effort and cost, but a second step, the addition of ISL functionalities will be mandatory to increase \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **DRS** & **PSL [+DRS]** & **ISL [+DRS]** \\ \hline Sensor Coverage & UP to 1000 km & Kilometers & Kilometers \\ Service Availability & - & ** & *** \\ Accuracy Improvement & **** & *** & *** [****] & *** [****] \\ User equip. complexity & ** & - [**] & *** [****] \\ Sensor complexity & * & ** [**] & *** [****] \\ Sensor weight and Dim. & * & [*] & *** [****] \\ Sensor cost & * & ** [**] & *** [****] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: General performance comparison for the different configurations. - = no change, * = Very Low, ** =Low, *** = Medium, **** = High. accuracy, availability, and continuity of the service, to meet the stringent requirements of Moon missions and ensure a safe, precise lunar navigation and landing. Furthermore, multiple local elements could also be considered for more demanding scenarios in the future.