[X] My Assistant

[helvick]

I've been trying to reconcile various crumbs of data regarding the Solar power systems on the MER's and have come to a point where I'm more or less stumped.

I've found the following papers that are repeatedly referenced in the many documents on the Web that evaluate solar power for martian exploration:
"Photovoltaic Array for Martian Surface Power" J. Applebaum, G.A. Landis, 43rd Congress of The International Astronautic Federation August 28-Sep 5 1992.
"Solar Radiation on Mars - Update 1991" J. Applebaum, G.A. Landis. NASA Technical Memorandum 105216

These provide a model for predicting insolation on the Martian surface taking into account Latitude, Tau and Mars orbit (ie LS, declination and distance from the Sun). The latter also gives some a pair of useful models for Tau by date and latitude during a major global storm.

Michael Allisons "Telling Time on Mars" Geophysical Research Letters Vol 24 No 16, Pages 1967-1970, August 15 1997. Gives some handy formulas for calculating time and the relevant orbital elements.

Between the lot I have a model that can replicate the examples provided in a bunch of MER documents (in particular the MER Environmental Requirements Document) and plots out nice daily\annual insolation data for any chosen site.

In order to be a bit more accurate I included the MER-A and MER-B actual Tau values for Sols 1-360 from the MER Analyst Notebook site.

What I want to do is establish what the initial theoretical power output from the panels should have been (to see how accurate the theoretical model is) and for that I need to know the actual surface area of the cells. Rupert Scammels site MER Technical Data says they consist of 55 strings of 20 cells, each measuring 4x2cm (ie 0.88m^2). If the cells are GaInP/GaAs/Ge triple junction cells at ~23.8% efficiency things look a bit low but pretty good (see the chart below). If I look at the rover self portraits though I count 501-505 individual cells and they look bigger than 4x2 to me. I reckon they are 4x6cm which gives a cell area of 1.2m^2, which is a number often listed on NASA sites. Unfortunately that value leads to power values that are waay to high - initial power ~ 1200wHr/sol for Opportunity.

Can anyone give me some definitive data on the efficiency of the cells used and their physical dimensions. Or give me some other explanation for the difference between what my calculations yield and reality.

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