## 2 Materials and Methods
### Preliminary Concepts and Simulation Configuration
#### 2.3.3 Scheduler  
The scheduler handles the activity of the different subsystems and decides if the subsystems can be powered on, for how long, and over which regions. Scheduler activity has been defined as a combination of Target Areas (TAs) to be observed and Ground Stations (GSs) to contact the satellite. When the satellite flows over them, different subsystems are turned on: either the payloads to acquire  
Figure 2: Accumulated radiation dose (rad) as a function of the shielding thickness. The main contributors to the Total Ionizing Dose (TID) include trapped protons and electrons and Bremsstrahlung protons. The total dose accumulated is efficiently reduced up to a 5 mm shielding thickness. data or the communication system to download data. The definition of these areas has a strong influence over the state of the satellite and the duty cycle of the different subsystems. In order to show representative simulation results, three TAs and three GSs have been considered in this mission analysis (Figure 3). The TA and GS over Europe overlap purposely because the UPC has a ground station located in the Observatori del Montsec [24], close to Barcelona. The scheduler decides which subsystem is active over which area, for how long, and under which budget conditions to achieve payload data fusion. In Figure 4, the data acquired by both payloads is depicted. The possibility to perform the data fusion with the optical payload on-board does not only depend on the simultaneous acquisition of data from both payloads. There are external factors, such as the meteorological conditions (i.e., clouds, fog) and the local time, that can disable the acquisition of optical data. Also, the specular reflection points can be located outside the optical swath of the camera, and therefore make data fusion impossible. To resolve this scenario, the track of the Sentinel 2A (equipped with a Multi-Spectral Imager) is also depicted to give an example of the possible use of another satellite's data to achieve the final product of the 3 Cat-3. Different scenarios can be dictated by the satellite's internal state, as well as by external factors that should be approached by a different set of rules. The scheduler's planning can never jeopardize the survival of the mission. The scheduler controls the activity and duty cycle of the different subsystems as sketched in Figure 5. The simulations presented in this report consider the following guidelines presented by priority-check order:  
Figure 4: Simulation of the 3 Cat-3 track (red), the swath of the optic instrument (red blurred), possible specular reflection points (green), the Sentinel 2A/B pass closer to the Catalan territory (cyan), and the swath of the optic instrument of the Sentinel 2A/B (cyan blurred). Figure 3: Target areas (TA) in red and ground stations (GS) in green considered for the simulation. The radii of the TAs (from left to right) are set to 3000 km, 3500 km, and 2000 km, respectively. The ground stations have a minimum elevation angle over the horizon of 10\({}^{\circ}\). 1. The thermal tolerance of all devices and materials on-board the satellite. The scheduler takes into consideration the energy dissipated in the form of heat by all devices on-board, as well as the Sun-eclipse periods experienced by the satellite. The heater will turn on if the temperature drops under a threshold and will not power off until the temperature reaches a certain level (5 \({}^{\circ}\)C and 8 \({}^{\circ}\)C, respectively). The batteries have the most restrictive temperature working range (between 0 \({}^{\circ}\)C and 45 \({}^{\circ}\)C); therefore, the hysteresis cycle that controls the heater prevents it from turning on/off constantly. 2. The impossibility to recharge the batteries in case of a total discharge as well as the maximum number of cycles of charge and discharge under different Depth of Discharge (DoD) levels as specified by the manufacturer (e.g., [25]). 3. The amount of data stored in the on-board memory.