A Case Study in NASA-DoD - The Black Vault

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Table B-2
POWER SUMMARY
Characteristic AEM STPSS MMS
Peak array power possible, W 238 a 1200 :6600 b
Average array power available
to space vehicle during
illumination, W 133 1200 3600
Average power available over
a low altitude orbit, W 68 500-600 1200
Average spacecraft housekeeping
power, excluding experiments
and associated
telemetry, W 28 100-200 350
Continuous or average power
available for experiments
over a low altitude orbit, W 40 400 850
aThe 238 W is the peak of the power curve which
roughly resembles a positive half sine wave, since the
array is not sun-tracking.
bThe 3600 W is set by the peak power handling capability
of the PRU; actually, there is no maximum since
still higher power arrays would merely be used less
efficiently. The excess electrical power would not be
drawn from the array, which merely results in a slightly
higher array temperature.
CThis assumes that power is supplied at a constant
rate to the spacecraft loads over the entire low altitude
orbit and that the battery capacity is adequate to
store the energy required over the period the array is
occulted.
dThe power bus is rated for 1200 W maximum, limiting
the total load that can be supplied.
however, optimizing the array power output is not likely to prove necessary.
Thus, there is a clear dichotomy in emphasizing peak power tracking
for efficiency in a multipurpose vehicle.
Some of the ±7 V variation of the MMS bus must be due to series
voltage drop in the PRU.
In addition to this slow dc variation, there
is a superimposed 70 Hz ripple caused by hunting of the peak power
tracker about the optimum. While this has been measured to be about