A Case Study in NASA-DoD - The Black Vault

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Appendix B
POWER SUBSYSTEM: A COMPARISON OF AEM, STPSS, AND MMS
by
N. E. Feldman and P. A. CoNine
BASIC DESCRIPTION OF THE AEM (3 1 )
The AEM spacecraft comes in two versions: Bot i have a standard
28 V power bus, a single 10 Ah rechargeable nickel cadmium (NiCd)
battery, and are powered by two fixed arrays (not .;un-tracking) with
approximately 23 sq ft of solar cells. (For further details, see
Table B-1.) The solar-cell arrays can provide a peak power of 238 W
end-of-life (EOL) when the sun angle is most favorable. Because the
arrays do not sun track, the average power produced during illumination
is about 130 W. However, to optimize power output in the orbit planned
for SAGE, the two solar arrays are driven to an angle of ±50 deg with
respect to the local horizontal. These motors are shown in the power
subsystem diagram of Fig. B-1.
Up to 50 W can be provided to the experiment module with a voltage
regulation of 28 V ±2 percent. Voltage regulation to the experiments
is relaxed for peak pulse loads above 50 W, e.g., the regulation is relaxed
to ±5 percent when the experiments require a peak pulse load of
120 W. ( 3 2 ) This peak pulse load option is used on the SAGE vehicle,
where the specification states that this 120 W load must be handled for
a maximum of 4 sec. Although the 4 sec time period is the specified
value, the spacecraft may be able to handle this amount of experiment
power for up to a few minutes.
The HCMM vehicle power budget during normal orbital operation,
i.e., standby, is:
Experiment
Telemetry
Attitude control and determination
Power circuitry
Total
22 W
4 W
12 W
12 W
50 W