# A New Orbiting Deployable System for Small Satellite Observations for Ecology and Earth Observation
## 2 Small Satellites for VIS, TIR, and MW Remote Sensing
### Evolution of Small Satellites  
The historical evolution of small satellites has been extensively presented in a number of other works (e.g., [22; 28; 29; 30; 31]); here we aim to provide only the main phases in order to contextualize our work. Small satellites were pioneered by a group of radio amateurs in California, who, in 1961, built and launched a 10 kg satellite, OSCAR-1 [32]. The first advance came in the subsequent years, with the addition of solar cells and rechargeable batteries, to allow small satellites to achieve useful lifetimes in orbit, and rudimentary attitude stabilization techniques (e.g., U.K. MoD Prospero, 66 kg, 1971). The transition to the \"modern\" small satellites occurred in 1981 with the launch of the 54 kg micro-satellite UoSAT-1 (University of Surrey Satellite), which included two in-orbit, reprogrammable microcomputers. UoSAT-1 was the first civilian satellite built to assess the feasibility of the design, construction, and launch of a scientific small satellite at a low cost. The U.S. Department of Defense started a LightSat initiative in the mid-1980s with the goal of reducing the costs and development time of satellites in the 50 to 1000 kg range [33]. During the 1980s, micro-satellites were considered of interest, but only for education and training. At the beginning of the 1990s, a number of commercial proposals were advanced for constellations of small satellites operating in low Earth orbit (LEO), in order to provide worldwide communications, focusing on services not provided by the geostationary Earth orbit (GEO) satellites. During the 1990s, micro-satellites were used for technology demonstration and the verification of new digital services, before the widespread deployment of terrestrial infrastructure, rudimentary EO, radio science, military applications, and training programs for developing space nations. A series of micro-satellites, developed at the Surrey Space Centre [34], demonstrated steadily improved EO capabilities, e.g., KITSat [35], designed for experimental satellite engineering, PoSAT [36; 37], 1 km ground sampling distance (GSD) for NIR, Thai-Phutt [22; 38], and the first multispectral imaging micro-satellite to achieve 300 m GSD NIR, Red, Green, and Blue, FASat-Bravo, that carried instruments to monitor the distribution and concentrations of the ozone [39]. Between the end of the 1990s and the beginning of the 2000s, the complexity and potential of small satellite development was encouraged by a series of international collaborations between emerging nations aiming to an affordable access to space. Modern small satellites have, therefore, become suitable for EO, especially via constellations, due to advancing technology and the lowering of costs of production. This was the case, for instance, for the Disaster Monitoring Constellation First Generation (DMC-1G), an international partnership based on a Know-How Transfer and Training program for Third Countries, featuring expense and problem sharing, and remote sensing data exchange between all the partners. The DMC-1G constellation was made up by five micro-satellites (~100 kg each), which were launched within a time window from 2002 to 2005, into a 686 km sun-synchronous orbit (SSO), and resulted in being particularly effective during the large-scale Indian Ocean Tsunami (2004) and Hurricane Katrina (2005) disasters [40]. The combination of commercial appeal and low unit cost brought small satellites to the center of attention in 2010, and stimulated proposals for new applications and business models [22]. The advent of small satellite constellations coupled to the Internet, Cloud storage, advanced processing, and distribution methods has fostered the change from science to commodity. The evolution of small satellite EO companies, e.g., RapidEye, SkyBox, BlackBridge, and Planet (Labs), has demonstrated the rapid changes and their market volatility. Specifically, RapidEye was operative since 2008 until a couple of years ago.