# _remote sensing_
## 4 Satellite Architecture and System Budgets
### Power Budget  
The power generation is evaluated considering the satellite in an SSO orbit with 10.30 a.m. orbit node local time. In this orbit, the angle between the Sun direction and the orbital plane has a slight seasonal variation with a worst-case maximum value of 25 degrees. Furthermore, since the deployed solar panels are oriented opposite to the HORUS payload, the power generation follows the orbital motion of the nadir-pointed payload, leading to a useful illumination only in half of the orbit. Whenever the payload is not nadir pointing, a sun pointing attitude is commanded, to improve the electrical energy generation. The optical payload remains activated when the combination of payload view angle and sun-angle is favorable, which can be conservatively assumed a range of \(\pm\)80 degrees from the subsolar point. Most of the on-board components are steadily activated, except for the UHF transmitter, which is active for about 15 min per day, the X-band transmitter, which is active for about two hours per day (see link budget and data budget discussion in Sections 4.3 and 4.4, the electric thruster, which is active on an average less than 5 min per day, as discussed in Section 4.5. The power budget is reported in Table 11, showing a positive margin of 2.11 W (about 6% of the average per-orbit power generation). The 2.11 W of margin gives confidence of maintaining all the subsystems operational in all the operating conditions. The reported power budget already presents worst case estimations for the operational power consumptions of each component, both in terms of peak power consumption and duty cycle. As an example, the AODCS systems report a peak power consumption of 4 W with 100% duty cycle, while the actual operations will very likely consider lower consumption values for the majority of the operational \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Subsystem** & **Mass (kg)** & **Margin** & **Mass with Margin (kg)** \\ \hline Structures and mechanisms & 1.700 & 10\% & 1.870 \\ OBDH & 0.200 & 5\% & 0.210 \\ EPS & 2.300 & 10\% & 2.530 \\ TT\&C & 0.600 & 5\% & 0.63 \\ ADCS & 1.300 & 10\% & 1.430 \\ ODCS & 1.000 & 10\% & 1.100 \\ Payload optical systems & 1.400 & 10\% & 1.540 \\ Payload data handling systems & 0.200 & 10\% & 0.220 \\ Harness & 0.400 & 20\% & 0.480 \\
**Total** & **9.100** & & **10.010** \\ \hline \hline \end{tabular}
\end{table} 
Table 10: HORUS nano-satellite indicative mass budget. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **Peak Power (W)** & **Duty Cycle** & **Average Power (W)** \\ \hline Solar panels’ generation & 75.4 & 0.44 & 33.20 \\ Main OBDH & \(-\)0.9 & 1 & \(-\)0.90 \\ TT\&C on board UHF transmitter & \(-\)3.0 & 0.01 & \(-\)0.03 \\ TT\&C on board UHF receiver & \(-\)0.4 & 1 & \(-\)0.40 \\ X-Band transmitter & \(-\)28.5 & 0.08 & \(-\)2.30 \\ ADCS + GPS & \(-\)4.0 & 1 & \(-\)4.00 \\ Thruster & \(-\)40.0 & 0.006 & \(-\)0.24 \\ HORUS camera system & \(-\)51.2 & 0.45 & \(-\)23.04 \\ Image acquisition system & \(-\)2.0 & 0.45 & \(-\)0.90 \\
**Margin** & & & **2.11** \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Power budget for average daily power consumption. time. Therefore, a similar power margin is considered reassuring with regards to the actual spacecraft operations in-orbit for the management of all subsystems. In some cases, commanded operations can consider a negative power margin (thus consuming the battery charge to continue the operations) for short amounts of time (one or few orbits). This can be done by extending the down link time to down link more data, when in visibility of more ground stations operating in coordination with the satellite or when performing longer orbit control maneuvers. The significant energy storage onboard the satellite batteries supports these operations, if relatively infrequent.