# Advances in Remote Sensing and Propulsion Systems for Earth Observation Nanosatellites
## 1 Introduction  
Nanosatellites and their subclass, CubeSats, are widely known for contributing to various applications and missions. Some of the applications are scientific research [1], education [2], Earth Observation (EO) [3], communication [4], and space exploration [5]. Nanosatellites are defined as satellites that weigh less than 10 kg. A specific category of nanosatellites, called CubeSats, come in different sizes but are all based on the standard CubeSat unit. This unit is a 10 \(\times\) 10 \(\times\) 10 cm cube that weighs between 1 and 1.33 kg. The modular unit, known as 1U, is multiplied to create larger nanosatellites, such as 2U, 3U, or 6U. Due to numerous launch and space rocket options, developing nanosatellites based on CubeSat standards is an inexpensive way to access space. According to the latest nanosats database ([[https://www.nanosats.eu/](https://www.nanosats.eu/)]([https://www.nanosats.eu/](https://www.nanosats.eu/))), accessed on 31 May 2024, the total number of nanosatellites and CubeSats launched, including launch failures, is 5000. This paper aims to thoroughly explore nanosatellite missions, explicitly focusing on their general and specialized applications, particularly in remote sensing for EO. The paper comprehensively analyzes the nanosatellite landscape by adopting a systematic review research methodology. Moreover, it discusses nanosatellites' key aspects and limitations, highlighting their abilities and restrictions. Also, we propose a comprehensive taxonomy of nanosatellites according to the propulsion systems. The ultimate objective is to contribute to the field by proposing directions for future research in nanosatellite remote sensing and propulsion systems, promoting advancements in this rapidly evolving area ofspace technology. Table 1 presents the most recent surveys regarding nanosatellites and their applications. [PERSON] and [PERSON] [6] provide a comprehensive global overview of small satellite developments over the past 50 years since the launch of Sputnik-1. They trace the evolution of satellites from the early, larger, and more complex systems, like Envisat, to the current trend of smaller, dedicated satellites designed for specific mission objectives, each carrying a single instrument. The article highlights the shift in satellite engineering, particularly the emergence of microsatellites in the early 1980s, driven by advancements such as the microprocessor. Surrey Satellite Technology Ltd. - SSTL (Guildford, UK) is credited with pioneering the design approach of using general-purpose buses and off-the-shelf components. The authors emphasize the global impact of this approach, with various companies and space agencies worldwide adopting SSTL's lead. Notably, microsatellite technology transfer programs have facilitated international collaboration, enabling engineers and scientists from different countries to participate in developing their microsatellites. The article also covers small satellite classification, initiatives in the USA and other parts of the world, technology and applications, and university-developed small satellites, including the CubeSats program. Furthermore, the authors discuss how small satellites are changing the economics of space by leveraging Commercial Off-The-Shelf (COTS) technology, enabling cost-effective and innovative observation missions despite the technical challenges involved. The article highlights the current operational and planned missions, including synthetic aperture radar (SAR) and hyperspectral imaging, underscoring the ongoing significance of small satellites in EO from space. [PERSON] et al. [7] focus on the evolution and growing significance of nanosatellites and CubeSats, initially conceived for educational purposes but now emerging as pivotal tools for EO. The authors highlight the affordability of nanosatellite constellations, their short development cycles, and the consequential increase in high-resolution Earth imagery, crucial for studying dynamic processes and monitoring the planet.