# RMCSat: An F10.7 Solar Flux Index CubeSat Mission
## 4 Satellite Architecture and Subsystems
### Power Budget  
There are four different power modes in which the satellite operates: Solar Observations, Solar Cruise, Eclipse Cruise, and Communication. Table 10 shows the power budget for the different modes. The peak power usage occurs during Communication, consuming up to 13.7 W.  
Communication occurs during one daylight passes of the ground station per day. As shown in Table 11, the average orbital power necessary is 9.4 W, for which the solar panels are designed to meet. Additional power can be drawn from the batteries during eclipse and peak power operations. \begin{table}
\begin{tabular}{l c c c c} \hline \hline  & \multicolumn{5}{c}{**Operation Mode (W)**} \\ \cline{2-5}
**Component** & \begin{tabular}{c} **Solar Ob-** \\ **servations** \\ \end{tabular} & \begin{tabular}{c} **Solar** \\ **Cruise** \\ \end{tabular} & \
\begin{tabular}{c} **Eclipse** \\ **Cruise** \\ \end{tabular} &
\begin{tabular}{c} **Communi-ctions** \\ \end{tabular} \\ \hline Primary payload antenna & 0.15 & 0.15 & 0.15 & 0.15 \\ Secondary payload antenna & 0.05 & 0.05 & 0.05 & 0.05 \\ Payload receiver & 2.50 & 2.50 & 2.50 & 2.50 \\ Electrical power system & 0.90 & 0.09 & 0.09 & 0.09 \\ \(\mathrm{S}\)-band communication patch & 0.05 & 0.05 & 0.05 & 0.05 \\ \(\mathrm{S}\)-band transmitter & 0.42 & 0.42 & 0.42 & 7.50 \\ UHF antenna & 0.04 & 0.04 & 0.04 & 0.04 \\ UHF transceiver & 0.00 & 0.00 & 0.00 & 0.48 \({}^{*}\) \\ Onboard Computer & 0.40 & 0.40 & 0.40 & 0.40 \\ ADCS & 2.05 & 1.10 & 1.10 & 1.10 \\ GNSS antenna & 0.05 & 0.05 & 0.05 & 0.05 \\ GNSS receiver & 1.30 & 1.30 & 1.30 & 1.30 \\ Integrated battery heater & 0.00 & 0.00 & 1.40 & 0.00 \\ Battery Charge (when in daylight) & 0.00 & 5.00 & 0.00 & 0.00 \\ \hline TOTAL & 7.9 & 11.2 & 7.6 & 13.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Power budget for RMCSat. Power consumption for the UHF is for the receiver only. 4W are consumed during UHF transmission, but this value would replace S-band transmitter consumption. \begin{table}
\begin{tabular}{l c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \begin{tabular}{c} **Downlink** \\ **S-Band (dB)** \\ \end{tabular} & \
\begin{tabular}{c} **Uplink VHF** \\ **(dB)** \\ \end{tabular} &
\begin{tabular}{c} **Downlink UHF** \\ **(dB)** \\ \end{tabular} \\ \hline Effective isotropic radiated power & 26.60 & 10.30 & \(-\)0.40 \\ Space loss & 168.14 & 144.37 & 153.89 \\ Receiver antenna gain & 34.5 & 0 & 10.7 \\ Receiver system noise temperature & 28.45 & 28.45 & 28.45 \\ Data Rate & 66.34 & 30.79 & 35.44 \\ Attenuation loss (1 degree elevation) & 1.72 & 0.02 & 0.16 \\ Calculated \(\mathrm{E_{b}}/\mathrm{N_{o}}\) & 25.06 & 35.27 & 20.38 \\ Required \(\mathrm{E_{b}}/\mathrm{N_{o}}\) & 9.6 & 16.4 & 16.4 \\ Polarization mismatch & 0.3 & 0.3 & 0.3 \\ Antenna pointing & 0.2 & 0.2 & 0.2 \\ System implementation & 1 & 1 & 1 \\ System losses & 1.5 & 1.5 & 1.5 \\ Link Margin & & & \\ (Calculated \(\mathrm{E_{b}}/\mathrm{N_{o}}\)-Required & 13.960 & 17.37 & 3.06 \\ \(\mathrm{E_{b}}/\mathrm{N_{o}}\)-System Losses) & & & \\ \hline \end{tabular}
\end{table} 
Table 9: RMCSat Communications Link Margin. The margin is determined using the calculated \(\mathrm{E_{b}}/\mathrm{N_{o}}\) less the required \(\mathrm{E_{b}}/\mathrm{N_{o}}\) and System Losses. Gallium Arsenide (GaA) triple-junction solar cells offer a production efficiency of 30% and performance degradation of 0.5% per year [28]. Based on these solar cells, the design orbital parameters, and an average solar incident angle of 45\({}^{\circ}\), the solar array power required is 18.0 W, or an array area of 864 cm\({}^{2}\). Using a cell size of 26 cm\({}^{2}\) and two cells per 1U, 17 1U panels would be required. While the deployable arrays and body-mounted cells provide 28U of the area and the capacity to generate 30.3 W, only 18U of cells is exposed to the Sun at any one time. The 18.0 W design provides a 20% power margin which allows for poor solar angles such as those at the terrestrial poles and for any cell failures.