**5. Conclusions**

Our study has demonstrated that small, cost-effective 1U CubeSats can be successfully used for the observation of SAA drift. Unlike the measurements introduced in Table 1, which were performed on large and heavy-payload satellites, we used a simply designed detector made of commercial off-the-shelf components that was able to operate for more than 20 months in an increased-radiation environment.

The results show that the method using the fitting of maximum fluxes is suitable for evaluating the drift rate in a large dataset. However, the centroid method normalized for the cosine-latitude effect requires less data to reach the same accuracy. Hence, the latter method is more suitable for CubeSats that have limited performance and data transfer.

We believe that a swarm of 1U CubeSats equipped with similar detectors could be used as a system for continuously monitoring the movement of the SAA. The advantage of such an approach is that individual CubeSats of the swarm can be placed in different orbits and at more suitable inclinations that would allow denser sampling in the SAA region. This would significantly improve the coverage and would allow more complex analysis of SAA drift. Such information would be beneficial for designing more accurate models of the SAA. As shown by [20], on the one hand, the drift of the SAA can change suddenly due to "geomagnetic jerks", which are not incorporated into the models. On the other hand, several studies have shown strong periodicity in SAA movement [13,21] which can be anticipated and foreseen by the models. For example, the ESA's Space Environmental Information System (SPENVIS) [8] models an average drift of the SAA of 0.3◦ in the westward direction and no movement in latitude, although a number of studies have observed slight movements in the northward or southward direction.

**Author Contributions:** P.K. developed a satellite UHF communication system ground station, the onboard computer, the satellite software, and the piNAV GPS receiver; he also processed satellite data and drew figures and prepared the parts related to the Lucky 7 satellite; M.S. prepared the introduction and interpreted the experimental results. Both authors have read and agreed to the published version of the manuscript.

**Funding:** The data processing and preparation of this document were supported by the European Regional Development Fund, Project CRREAT no. CZ.02.1.01/0.0/0.0/15 003/0000481.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data that support the findings of this study are available from the author upon reasonable request.

**Acknowledgments:** The authors would like to thank Jaroslav Laifr for building the Lucky 7 CubeSat and developing the piDOSE radiation detector.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

