Page 194 - Intro to Space Sciences Spacecraft Applications

Spacecraft Systems
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Several design selections must be made, such as either rigid or flexible
arrays and types of solar cells and batteries. Typical battery performance
values are shown in Table 8-6. The results of the power subsystem design
include EOL and BOL power, determination of solar panel area and mass,
number of batteries and their mass, and power control unit, regulator/con-
verter, wiring, and total subsystem mass.

Table 8-6
Spacecraft Battery Characteristics

~~~
Specific Energy Density Allowable
(SMb) Depth of
Battery Type (kglwatt hrs) Discharge (YO)
1 NiCd 0.040 22
2 NiH, 0.025 60
NiCd: Nickel-Cadmium
NiH,: Nickel-hydrogen

Power Subsystem Design Calculations. As indicated, mission and pay-
load inputs have an important influence on the power design calculation.
The final orbital altitude, inclination, and mission lifetime determine the
solar degradation rate based on established curves and sets the day/eclipse
times that will determine the amount of time the solar cells will be creat-
ing power and the amount of time that the payload and supporting systems
will rely on battery power. The power required by each element of the
payload, the payload duty cycle, and the day/eclipse profile sets the stage
for the subsequent system power estimation for the entire satellite. After
the baseline power requirements for the satellite are established, the
designer makes several important selections that will influence the system
mass based on the type of solar array and solar cell desired:

Rigid Array: Derives the mass of the solar array from
the solar cell power data base (Table 8-4).
Select the Solar Cell Vpe: Derives the size of the solar array based on
the solar cell database (Table 8-4).
SSF Silicon Single-sided fixed silicon
Thin Si Thin silicon
GaAs/Ge Gallium arsenide/germanium