# Advances in Remote Sensing and Propulsion Systems for Earth Observation Nanosatellites
## 6 Conclusions  
This paper presented a survey of nanosatellites' applications and a taxonomy according to the propulsion systems. We focused on EO, which included vegetation [14; 15; 16; 17; 18; 19; 20], natural disasters [21; 23; 24; 25; 26], inland water monitoring [27; 28; 29; 30; 31; 32], and oceanography [33; 34; 35; 36; 37; 38]. We also presented some special applications of nanosatellites, such as nanosatellite constlation as an IoT communications platform [43]. Finally, we presented the fundamentals of propulsion and the main systems used for propulsion.  
Nanosatellites have become essential tools for space-based remote sensing, especially for organizations with limited budgets. Their affordability, quick development cycles, and faster deployment are particularly useful in responding to dynamic situations such as disaster response and environmental monitoring. Deploying nanosatellites in constellations enhances their utility, allowing frequent revisits to specific areas on Earth for vital applications such as monitoring vegetation health [14; 15; 16; 17; 18; 19; 20], tracking maritime activities [33], and assessing urban development [40]. Despite their compact size, nanosatellites can accommodate diverse sensors and payloads, supporting precision agriculture, environmental monitoring, and testing innovative space technologies. Nanosatellites play a crucial role in disaster response by providing rapid and updated information on natural disasters, which helps assess damage and coordinate relief efforts. Collaborating nanosatellites with other satellites contributes to a more comprehensive understanding of Earth's processes, showcasing their significance in advancing space exploration and observation capabilities.  
However, while nanosatellites offer significant advantages in terms of cost-effectiveness and accessibility, it is crucial to acknowledge and address their inherent limitations. The size constraints impose restrictions on payload capacity, impacting the execution of complex scientific experiments and the quality of data collected. Additionally, limitations in power generation, storage, and communication bandwidth affect nanosatellites' operational capabilities and real-time data transfer. The vulnerability to the space environment, given their limited space for protective shielding, poses risks to reliability and mission lifespan. Furthermore, orbital restrictions and the need for advanced propulsion systems raise challenges in optimizing orbits for specific missions and avoiding collisions in an increasingly crowded orbital space.  
Numerous studies have been conducted on the functionality of nanosatellites, their payloads, and their applications in EO. However, further research is still needed to address nanosatellites' limitations and improve their effectiveness and sustainability in various scientific and EO applications. Also, further research is needed to develop propulsion systems optimized according to the characteristics and limitations of nanosatellites.  
Conceptualization, G.F. and T.L.; methodology, G.F. and T.L.; validation, T.L., V.A. and P.S.; investigation, G.F. and T.L.; resources, V.A. and P.S.; data curation, G.F.; writing-- original draft preparation, G.F.; writing--review and editing, G.F. and T.L.; visualization, G.F.; supervision, T.L., V.A. and P.S.; project administration, V.A. and P.S.; funding acquisition, V.A. and P.S. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflicts of interest.