References:
Expected energy generation
ISS orbit is 92.7 minutes with 36 minutes in eclipse. That is 140º out of 360 of eclipse.
Cubesat standard photovoltaic triple junction cell has a maximum electrical power of 2400 mW. Howover, MPPT has a efficient of 90%.
Se define la irradiancia como la densidad superficial de potencia: $$ B_0 = 1367 \ W/m^2 $$
Solo el 70% de la radiación solar termina por llegar al suelo y ser absorbida.
I am going to supose that we will use Triple Junction GaAs Solar Cell: $$ V_{op} = 2350 mV \\ I_{op} = 417 mA \\ \text{Effiency} = 29.5 \% \\ \text{MPPT Effiency} = 0.9 \\ \text{Absorbed Solar radiation after atmosphere} = 0.7 \\ 1350 \cdot 0.3 \cdot 0.7 \cdot 0.9 = 255.15 [W/m^2] \\ \text{End of life} = 2 \% \text{per year} \\ 255.15 \cdot 0.98 = 250 [W/m^2] \\ \text{Para generar 10W necesitarmos} = 0.04 \ m^2 \\ \text{Cell Area} = 26.51 \ cm^2 \\ \text{total cell} = 16 \\ \text{Utilizaremos } 18 \text{ cells} $$
6 x 3 celulas.
Células de 4 x 7. Nos caben dos células por cada pared.
18 celdas, 2 en cada panel… 9 paneles.
Calcular cual es la mejor forma, si desplegado o .
Diferentes disposiciones:
Diposición número 1
Un única cara con 18 celdas. Su valor máximo de potencia es de 11.9 W. Su media de potencia será de 3.68 W.
Teniendo en cuenta que tendremos aproximadamente 140º de eclipse, el peor escenario es el siguiente:
Dónde la potencia media generada con eclipse será de 2.19 W. Esto es que la mínima energía generada será de 2.19 W x 1.54 h = 3.3726 Wh.
Disposición número dos
La disposición en la que una cara siempre está mirando a tierra y 3 caras tienen 6 celdas. La potencia máxima es de 5.6 W. Su potencia media será de 3.68 W.
Con eclipse se quedaría de la siguiente forma:
En el que la potencia media en este escenario será de 2.19 W. Esto es que la mínima energía generada será de 2.19 W x 1.54 h = 3.3726 Wh.
Expected Power Consumption
| Module | Peak [mW] | Average [mW] | Normal Mode [mW] | Safe Mode [mW] | Note |
|---|---|---|---|---|---|
| EPS | 200 | 75 | 75 | 75 | 1 |
| Battery Heaters | 200 | 200 | 40 | 40 | 2 |
| ADCS | 1500 | 300 | 60 | 60 | 3 |
| Magnetorquers | 775 | 775 | 39 | 0 | 4 |
| Reaction Wheels | 1500 | 750 | 156 | 60 | 5 |
| OBC | 500 | 320 | 64 | 60 | 6 |
| COMMS RX | 400 | 300 | 60 | 30 | 7 |
| COMMS TX | 2000 | 750 | 83 | 60 | 8 |
| Payload 1 [Ka-band] | 1000 | 375 | 42 | 60 | 9 |
| Payload 2 [Ku-band] | 1000 | 375 | 42 | 60 | 10 |
| Payload 3 [Star-tracker] | 1000 | 250 | 150 | 60 | 11 |
| Total | 10075 | 4470 | 811 | 565 | 12 |
| Energy losses | 4324 | 1918 | 348 | 243 | 13 |
| Total + Losses | 14399 | 6388 | 1159 | 808 | 14 |
Notes:
- 3: Considering the peak power of the GPS.
- 2: Temporaly value. Taken from Upsat
- 4: Temporaly value. Taken from Lisboa TFM
- 6: CC3200 have several modes for power saving. I am taking a mean value.
- 10: Only emitting when there is LOS from tenerife (maximum of 60 minutes per day)
- 11: Only emitting when there is LOS from tenerife (maximum of 60 minutes per day)
- 13: Considering the 70% of the input power
Expected a minimum availabe power coming from the solar panels of 4.5W.
Energy Budget
Considering ISS Orbit of 92.5 (1.54h) minutes, where 36 minutes is eclipse.
| Energy Figures | CubeSat in Safe Mode | CubeSat in Normal Mode |
|---|---|---|
| Energy Generated / Orbit [mWh] | 3370 | 3370 |
| Consumed Energy without Losses / Orbit [mWh] | 870 | 1249 |
| Energy Losses / Orbit [mWh] | 373 | 536 |
| Consumed Energy / Orbit [mWh] | 1243 | 1785 |
Power Management during Phase
LOS Tenerife
| Module | Peak [mW] | Safe Mode [mW] | Note |
|---|---|---|---|
| EPS | 200 | 75 | 1 |
| Battery Heaters | 200 | 40 | 2 |
| ADCS | 1500 | 60 | 3 |
| Magnetorquers | 775 | 0 | 4 |
| Reaction Wheels | 1500 | 60 | 5 |
| OBC | 500 | 60 | 6 |
| COMMS RX | 0 | 30 | 7 |
| COMMS TX | 0 | 60 | 8 |
| Payload 1 [Ka-band] | 1000 | 60 | 9 |
| Payload 2 [Ku-band] | 1000 | 60 | 10 |
| Payload 3 [Star-tracker] | 1000 | 60 | 11 |
| Total | 10075 | 565 | 12 |
| Energy losses | 4324 | 243 | 13 |
| Total + Losses | 14399 | 808 | 14 |
Batteries
TODO: Revisar cálculos
Assuing we will use APR18650 batteries. That is 1.1Ah, 3.3V.
The solar panel bus is 12V. So, we need 3 18650 in series.
36 minuttes of clipse.
$$ \frac{1159 \cdot 10^{-3}}{12} = 100 \ mA $$
That is way less than 1.1 Ah.