## 4 Case Studies  
### SBSS Scenario  
Globally, the UAE is classified as a country with a high vulnerability to climate change, adversely affecting the infrastructure, human health, and natural habitat, which in turn impacts various sectors and policies including socioeconomic, health, and environment [79]. Adding on to the problem of climate change are intermittent events of oil spills that have a long term effect on eco-systems and economies. An Earth observation constellation comprising 40 satellites evenly spaced across four orbital planes with RAAN distributed between 0 degrees and 360 degrees (i.e., 0, 90, 180, 360) as illustrated in Figure 5 is hypothesized to detect oil spills, monitor climate change, and track RSOs simultaneously for SA and CA. The spacecraft in the DSS constellation are assumed to be placed in nearly circular arrangement (eccentricity = 0.001) at an altitude of 500 km at an inclination of 99 degrees, and are equipped with a hyperspectral payload with artificial intelligence (AI) to process the data on-board of the satellite for oil spill detection and climate change analysis [80; 81; 82]. The characteristics of the on-board payload are listed in Table 2. To ensure the safety of DSS assets, the DSS constellation performs RSO tracking and establishes a collaborative exchange of tracking information through inter-satellite links to accomplish AN (AN) for CA [83; 84]. The DSS constellation also acts as a service provider for other operational satellites or sub-orbital vehicles by establishing a data exchange using inter-satellite links so that they can perform AN for CA, as illustrated in Figure 6.  
In recent studies, star trackers have been investigated as an alternative sensor for debris surveillance [85]. The participating spacecraft in the constellation are equipped with star trackers for attitude determination and RSO tracking. The spacecraft are assumed to simultaneously perform Earth observation operations along with AN for CA. RSO tracking and detection are performed using optical sensors and star trackers due to [86]:  
* The passage of the RSO across the sensor's field of view [10]. * The exploitation of brightness, angular velocity, and other threshold parameters for RSO travelling across the FOV of the sensor [87]. The major focus is to come up with a suitable mission architecture that accomplishes Earth observation and SSA mission objectives expeditiously. The requirements of the mission architecture are as follows:  
* The system configuration must be feasible for multiple applications. For instance, AN for CA (current interest), SBSS for STM, multi-domain traffic management (MDTM) [88], and point-to-point sub orbital space transport, which are envisioned in the longer term. * The satellites in the DSS architecture should complement each other and form ad-hoc or optional teams to make autonomous decisions and maximize mission objectives without involving the ground control segment, making them distinct compared to conventional satellite systems. \begin{table}
\begin{tabular}{c c} \hline \hline
**Payload** & **HyperScout-2** \\ \hline Field Of View (FOV) & channel 1: 31\({}^{\circ}\)\(\times\) 16\({}^{\circ}\) \\  & channel 2: 31\({}^{\circ}\)\(\times\) 16\({}^{\circ}\) \\ \hline Ground Sample Distance (GSD) & channel 1: 75 m \\  & channel 2: 490 m \\ \hline Swath & 310 \(\times\) 150 km \\ \hline Active Pixels & channel 1: 4000 \(\times\) 1850 px \\  & channel 2: 1024 \(\times\) 768 px \\ \hline Spectral Range & channel 1: 400–1000 nm \\  & channel 2: 8000–14,000 nm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Hyperspectral payload specifications. Figure 5: (**a**) Proposed DSS constellation with 4 orbital planes (not to scale); (**b**) Simplified DSS system architecture for a single orbital plane.