## 5 Power System Design
### Power System Configuration  
The purpose of the PMAD is to manage and distribute power to all components and Sub-Systems safely, maximizing efficiency and maintaining safe operation. The PMAD can convert voltage to a suitable input for the feeding components a PMAD typical CubeSat Operation is outlined by [3]. It is assumed that the on-board computer, antenna, magnetorquer board, GPS and payload are electrically consuming power for the entire duration of the mission [3], this gives a baseline for the power consumption, Figure 39, of the system. The nominal power consumption of the electrical system is equal to the sum of the consumption of the 5 components this isustrated by Figure 39.  
\[\mathrm{P_{baseline}}\ =\ 0.175\ \mathrm{W}\ +\ 0.04\ \mathrm{W}\ +\ 0.55\ \mathrm{W}\ +\ 0.12\ \mathrm{W}\ +\ 1.9\ \mathrm{W}\ =\ 2.785\ \mathrm{W} \tag{10}\]  
Figure 39: Baseline Power Draw of the CubeSat Electrical System Hot Phase. \[\mathrm{P}_{\mathrm{data\ processing}}\;=\;0.175\,\mathrm{W}\;+\;0.04\,\mathrm{W}\;+ \;0.55\,\mathrm{W}\;+\;0.12\,\mathrm{W}\;+\;1.9\,\mathrm{W}\;+\;0.48\,\mathrm{W} \;=\;3.265\,\mathrm{W} \tag{11}\]  
The data processing electrical scenario adds the power consumption of the transceiver onto the base power draw of the CubeSat, it has been decided that data processing will only occur during the hot phase, to preserve the charge of the battery during the cold phase. The on-board computer possesses 16 GB of storage, which will allow all data to be stored safely during the cold phase generated by the payload as the payload only generates 2.5 Mb of data per day [9]. \[\mathrm{P}_{\mathrm{ac}}\;=\;0.175\,\mathrm{W}\;+\;0.04\,\mathrm{W}\;+\;0.55\, \mathrm{W}\;+\;0.12\,\mathrm{W}\;+\;1.9\,\mathrm{W}\;+\;0.04\;+\;0.6\;+\;0.54\; =\;3.965\,\mathrm{W} \tag{12}\]  
The altitude control scenario assumes simultaneous operation of the propulsion system, magnetorquer rods and reaction wheels as a worst-case AD&C scenario. The value of consumption of the propulsion system is to maintain the CubeSat's orbit, and does not factor orbital maneuvers or adjustments to altitude [4]. Figure 42: Constant Consumers Cold Case Block Diagram. Figure 43: Cold Case Altitude Control Block Diagram. During the eclipse phase, the solar panels will no longer be generating power as no solar flux is incident to the cells. This produces a baseline power draw diagram identical to the hot case, without the input of solar panels. It is, therefore, required that the battery stores enough energy during the hot phase to power the sub-systems during the cold phase. It is assumed that an instantaneous transition occurs from the hot to cold phase. It is necessary to conduct an electrical energy balance analysis upon the CubeSat's orbit to ensure enough power is available always to power each sub-system. For the hot-case scenario, the energy balance will assume that the baseline power draw is active 50% of the time, the altitude control draw is active 25% of the time as a worst-case scenario, and that the data processing scenario is active 100% of the time. Based on mission analysis the hot phase has duration of 60 min and 52 s (3652 s), and the cold phase duration of 35 min and 38 s (2138 s). Assuming a constant power generation of 7 W for the hot phase [10], the total energy generated by the panels is equal to:  
\[\mathrm{P(hot\;phase\;generated)}\ =\ 7\ \mathrm{W}\ *\ 3652\ \mathrm{s}\ =\ 25,564\ \mathrm{J} \tag{13}\]  
The power consumed during the hot phase is equal to:  
\[\mathrm{PConsumed}\ =\ (2.785\ \mathrm{W}\ *\ 1826\ \mathrm{s})\ +\ (3.265\mathrm{W}\ *\ 913\ \mathrm{s})\ +\ (3.965\ \mathrm{W}\ *\ 913\ \mathrm{s})\ =\ 12015.08\ \mathrm{J} \tag{14}\]  
Assuming a 3% loss in the charging and discharging process of the battery and a 10% loss in the PMAD system [19] the efficiency of the system can be factored into the total power generation to yield an estimation of actual power production.