Page 192 - Intro to Space Sciences Spacecraft Applications

Spacecraft Systems 179

satellite's end-of-life (EOL) power requirement, working backward to
determine the satellite's beginning-of-life (BOL) power requirement.
BOL power is higher because solar cells degrade over the mission lifetime
(influenced by solar cell type, mission altitude, and inclination), and the
solar panels must be large enough to guarantee adequate EOL power.
When the BOL power requirements are known, the next step is to size the
solar array, batteries, power regulation, control, and distribution systems.
Solar cell BOL wattdarea and wattdmass are selected from a database,
such as the example provided by Table 8-4 which lists average values for
various solar cell types and array architectures. Solar array sizing takes
into account the solar cell type sun incidence angle, battery type, eclipse
cycle, power duty cycle, stabilization method, and other related factors.
Solar eclipse cycle times versus spacecraft circular orbit altitude are illus-

c 7 -
SERIES
SERIES
I REGULATOR I I REGULATOR
- DISCHARGE
SOUR REGULATOR "zzz
ARRAY
I (FULL LOAD LOAD
OR
PARTIAL) I '
SOUR BArnRY
ARRAY LOAD

0 OPnONAL E= ELEUEMS
I
Figure 8-9. Electrical power subsystem configuration options.

Table 8-4
Solar Cell Design Characteristics

Type Rigid Array Flexible Array
Power Mass Power Mass
Name (wattdm2) (watts/kg) (wattdm2) (wattskg)
1 SSF Silicon 153 28 153 84
2 ThinSi(APSA) 153 30 153 115
3 GaAsIGE 218 39 218 110
4 CleftGaAs 223 45 223 163
5 GaAsCulnSe2 272 51 212 150