Question

You are designing a spacecraft that will use Gallium Arsenide (GaAs) solar cells for power production for a near-Earth mission. The following parameters are given:

            Time in daylight = 68 minutes

            Time in eclipse = 22 minutes

            Power required in daylight = 330 watts

            Power required in eclipse = 100 W

            Path efficiency in daylight = 0.85

            Path efficiency in eclipse = 0.65

            a) What is the power required from the solar array during daylight periods?

            b) What is the “beginning-of-life” power per unit area of the solar array?

                        Assume worst-case Sun angle and nominal inherent degradation.

            c) What is the “end-of-life” power per unit area of the solar array?

                        Assume a 5-year mission

                        Life degradation per year = 2.75%

            d) What is the required area of the solar array?

            e) What is the required capacity of the secondary batteries pf the spacecraft?

                        Assume the following:

Limit on battery’s depth of discharge (DOD) = 20%

                                    One battery only on spacecraft

                                    Battery discharge voltage = 27.1 volts

                                    Transmission efficiency between battery and load = 90%

Answer 1

Part a)

P_{solar array} = {[100*22/0.65]+[330*68/0.85]}/78

=381.85 W

power required from the solar array during daylight periods is 381.85 W

Part b)

Given Worst case sun angle: 23° and nominal inherent degradation

We assume,

24% efficient solar cells (n)

0.95 packing factor (I_p)

0.9 temperature loss (I_temp)

No shadowing losses (I_s)

Perfectly pointed arrays

The "beginning-of-life" power per unit area of the solar array,

P_b-o-l = 1358 * n * I_p * I_s * I_temp * cos (theta)

        = 1358 * .24 * 0.95 * 1 * 0.9 * cos 23

The "beginning-of-life" power per unit area of the solar array is 256.5 W/m²