# A New Orbiting Deployable System for Small Satellite Observations for Ecology and Earth Observation
## 1 Introduction  
Remote sensing, from visible (VIS), through thermal infrared (TIR), up to microwaves (MW), represents a key tool to study and monitor our planet, especially when field measurements are hard to produce because of environmental coverage (e.g., oceans) and/or technical and operational issues (e.g., inaccessibility, or seasonal or annual variations). Remote sensing multispectral data are critical to monitor the results of human activities, e.g., polluting gases or industry-made products, and natural hazards, e.g., hurricanes, floods, fires, earthquakes, volcanic eruptions, sandstorms, soil erosions, and landslides [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14], whereas the availability of more frequent views over the same area allows for a better management of natural hazards and disaster e.g., [15]. These datasets allow for the development of strategies for the safeguarding of natural habitats, plants, and animal species (e.g., [16; 17; 18; 19; 20]). Although a great return is guaranteed, remote sensing performed by standard satellites is very expensive [21], and is thus affordable only to countries and large consortia able to ensure expensive, long-term operations. The high costs are due to large volumes and masses (>1 m\({}^{3}\), >500 kg) of the standard satellites, which imply the need for powerful launchers. In the late 1980s, the technological advancement of small satellites [22], classified in different classes depending on their masses (cf. Table 1), allowed for space programs to also become accessible to countries, communities, and private institutes with limited funding (e.g., [23]). Furthermore, small satellites represent ideal platforms to test and validate new, cutting-edge technologies. The limited on-board resources indeed require innovative propulsion methods (including electric propulsion and compressed gas or liquids, e.g., butane and carbon dioxide), attitude control, communication, and computation systems. Micro-satellites use innovative compact communication systems (e.g., optical transceivers, antenna arrays, and satellite-to-satellite data relay), in the VHF (very high frequency), UHF (ultra high frequency), and L-, S-, C-, and X-bands. In particular, a remote sensing payload operating in VIS, TIR, and MW onboard small satellites represents a great challenge to balance miniaturization and performance, because the achieved resolution depends on the size of the signal collector. A novel solution is offered by the deployable approach, which allows to both minimize the instrument volume at the launch phase and achieve good performances at the orbital phase (once unfolded). For Earth Observations (EO), deployable optics can become an asset to gain those accurate, precise, and frequent measurements required to keep monitoring natural and human activities [24]. Alongside any technical arrangements, the increasingly widespread data fusion techniques rely on merging data from different sensors to ameliorate the quality of the final output, as regards spatial resolution, geometry, and topography (e.g., [25]). In this paper, we reviewed several marine and atmospheric studies, as representative cases (i) to highlight the improvements in accuracy, resolution, and spatial/time coverage when using remote sensing payload onboard small satellites, and (ii) to validate the performances of a deployable telescope, currently under development, targeting ecological questions. In Section 2, we present a short introduction about \begin{table}
\begin{tabular}{c c} \hline \hline
**Small Satellite Class** & **Mass [kg]** \\ \hline Mini & 100 to 500 \\ Micro & 10 to 100 \\ Nano & 1 to 10 \\ Pico & 0.1 to 1 \\ Femto & \textless{}0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Small satellite classification according to their mass adapted from [21; 26; 27]. remote sensing payloads for EO, along with DORA, the new deployable system that is investigated in this study.