# Advances in Remote Sensing and Propulsion Systems for Earth Observation Nanosatellites
## 5 Discussion
### Limitations  
Besides the numerous advantages of nanosatellites, such as low-cost development and launching, there are some limitations, mainly due to size constraints, such as the limited payload capacity, which is a constraint for many types and amounts of instruments or sensors' resolution [76]. This limitation significantly impacts the ability to execute complex scientific experiments or observations. It can affect the resolution and accuracy of scientific or EO data. Also, the nanosatellites' small size may preclude including extensive fuel reserves. Once onboard resources are depleted, the satellite becomes non-operational, so the nanosatellites' mission lifespan is often short. Furthermore, there are some security issues in satellite communication systems in nanosatellite constellations, considering their characteristics [77].  
Another constraint due to their small size is the limit of power generation and storage, which can affect the operation of energy-intensive payloads or prolonged mission durations, especially in regions of space where sunlight for solar panels is scarce [78]. Also, nanosatellites typically have lower communication bandwidth, which can impact the volume and speed of data transfer. This limitation may affect real-time communication and the amount of data transmitted to Earth [79].  
The nanosatellites' vulnerability to the space environment is a constraint due to the small form factor of nanosatellites providing limited space for protective shielding, which makes them more susceptible to radiation, temperature extremes, and micrometeoroid impacts, potentially affecting their reliability and lifespan [80].  
Nanosatellites often have orbital restrictions due to being deployed as secondary payloads, which means they have limited control over their orbital parameters. This constraint may restrict their ability to choose optimal orbits for specific missions or applications. Furthermore, many nanosatellites need advanced propulsion systems, making it challenging to perform complex orbital maneuvers or adjust their orbits for specific observation requirements [81]. Also, the increasing number of nanosatellites in orbit is critical, which raises concerns about the risk of collisions and adds to the growing issue of space debris. The lack of propulsion systems in some nanosatellites makes it difficult for them to actively avoid potential collisions. Therefore, developing small propulsion systems for nanosatellites based on the main fundamentals is very important for avoiding collisions and, even more, the ability to choose and adjust their orbits according to the needs of their applications.  
As highlighted in ESA's project on 'An Inventive High-Thrust Micro-Propulsion System Compatible with Small-Satellites' Safety and Budget Requirements', integrating miniaturized propulsion systems remains a significant challenge due to thermal management and propellant storage constraints [82]. Additionally, ENPULSION's report on 'The first 100 FEEP propulsion systems in space' emphasizes the need for efficient designs to enable long-term operations in nanosatellite missions [83].  
Even more, [PERSON] and [PERSON] [84] note that small satellites face relatively stronger air drag compared to their larger counterparts. This results in accelerated orbital decay, particularly during geomagnetic storms, requiring nanosatellites to operate at higher altitudes to achieve comparable lifetimes. This trade-off has implications for propulsion requirements and mission design.