## 2 Survey of Commercial Small Platforms  
This section presents the results of a comprehensive survey of commercial Low Earth Orbit (LEO) small platforms for EO, in order to properly select the platforms for each technology. To do this, the capabilities and limitations of the small commercial buses are taken into account. A total of forty-two commercial platforms from eighteen different companies have been identified, and their information has been compiled from company websites and conferences proceedings (Appendix A). These small platforms cover a wide range of payload mass and power. They are categorized into three groups nano-, micro-, and mini-satellites. Table 2 summarizes their typical parameters. These platforms support payload masses from 1 kg to 600 kg [9], payload powers (orbital, average) from 1 W to 1500 W [10], downlink up 15 Mbps (S-band) [11], 100 Mbps (X-band) [12], and 1.2 Gbps (K-band) [13]. In this context, the recent evolution of the capability of micro- and mini-class platforms, and the payload miniaturization have demonstrated being a true competitor of large spacecrafts for some applications. Table 3 summarizes the capabilities of CubeSat EO platforms (3U, 6U, and 27U). Nanosatellites are now becoming popular thanks to the CubeSat standard. Typical CubeSat missions can be implemented in 1 to 3 years, with typical budgets from 200 K to 1 M $ USD, including launch. On the other side, ESA has promoted the development of a generic Small Geostationary Platform [14] (SmallGEO or SGEO) industrialized by OHB [15]. This flexible and modular platform has a lifetime of up to 15 years, a payload mass of up to 400 kg, and a payload power of up to 4 kW [16]. This platform was originally proposed to help European industries in the commercial telecom satellite market. However, the Earth Observation domain can also benefit from the capability of this platform in terms of available power and payload mass. In this way, an analysis of the EO technologies that are appropriate for use in small platforms is conducted in the next section. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Classification**} & **Satellite Mass** & **Max. Payload Mass** & **Max. Payload Power** & **Max. Data Rate** \\  & **[kg]** & **[kg]** & **(average) [W]** & **(Downlink)** \\ \hline Nano & \(<\)10 & \(\leq\)3 [17] & \(\leq\)15 [11, 18] & \(\leq\)15 Mbps [19] \\ \hline Micro & 10–100 & \(\leq\)54 [20] & \(\leq\)150 [21] & \(\leq\)160 Mbps [22] \\ \hline Mini & 100–1000 & \(\leq\)600 [9] & \(\leq\)1500 [10] & \(\leq\)1.2 Gbps [13] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of survey of commercial small platforms capabilities. Figure 1: Design process to select payload and platform according to the requirements. Survey of Earth Observation Sensors and Measurements Requirements to Cover the Future Gaps on Copernicus  
EO satellites have revolutionized the study of the environment, and are contributing to a more rational use of the natural resources, and environmental protection. The applications of the data supplied by these systems are enormous: disaster monitoring, weather forecast, maritime safety, marine resources monitoring, forestry, vegetation state, water cycle, energy budget, pollution control, water quality, climate change, and security; using radars, microwave and optical/IR radiometers, optical imagers or scanners. Table 4 presents the generic classification of the remote sensors. Instruments are classified in the following four categories: active or passive, either microwave or optical. Optical sensors measure the signals received around the visible part of the spectrum, from the Ultra-Violet (UV) to the Thermal Infrared (TIR). Microwave sensors use the signals in the microwave and millimetre-wave parts of the spectrum, typically from 1 GHz to 1 THz. Passive systems are based on the collection of the electromagnetic waves that are emitted/scattered by external sources, such as the Sun or other bodies.