In the example of the International Space Station (ISS) problem, the Electrical Power System (EPS) consists of the solar arrays, the batteries, the Battery Charge-Discharge Unit (BCDU), the DC Switching Unit, and a set of DC-to-DC Conversion Units (DDCU) connected as shown in the diagram. The entire system was modeled using a NASA-developed code specific to the ISS electrical power system called SPACE. A 5-element set of input uncertainties were assigned that included one environmental variable (Earth albedo).  Since the efficiencies of the BCDU and the DDCU’s are a function of the power level, the entire curves for these variables were handled as a single uncertainty.  N&R Engineering coupled the NASA SPACE code with its own SUA code to perform the probabilistic analysis.


The results showed a mean power level (per panel) of 13.72 kwwith a 0.138 kwe standard deviation, although the power could vary between 13.2 and 14.2 kwe.  The DDCU efficiency and the spacecraft altitude error are the most important uncertainties.  This information helps mission operators plan the power allocation more effectively.

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