Modeling solar cell degradation in space: A comparison of the NRL displacement damage dose and the JPL equivalent fluence approaches

The method for predicting solar cell degradation in space radiation environ ments developed recently at the US Naval Research Laboratory (NRL) is compa red in detail with the earlier method developed at the US Jet Propulsion La boratory (JPL), Although both methods are similar, the key difference is th at in the NRL approach, the energy dependence of the damage coefficients is determined from a calculation of the nonionizing energy loss (NIEL) and re quires relatively few experimental measurements, whereas in the JPL method the damage coefficients have to be determined using an extensive set of exp erimental measurements. The end result of the NRL approach is a determinati on of a single characteristic degradation curve for a cell technology, whic h is measured against displacement damage dose rather than fluence, The end -of-life (EOL) cell performance for a particular mission can be read from t he characteristic curve once the displacement damage dose for the mission h as been determined In the JPL method, the end result is a determination of the equivalent I MeV electron fluence, which would cause the same level of degradation as the actual space environment. The two approaches give simila r results for GaAs/Ge solar cells, for which a large database exists. Becau se the NRL method requires far less experimental data than the JPL method, it is more readily applied To emerging cell technologies for which extensiv e radiation measurements are not available. The NRL approach is being incor porated into a code named SAVANT by researchers at NASA Glenn Research Cent er. The predictions of SAVANT are shown to agree closely with actual space data for GaAs/Ge and CuInSe2 cells flown on the Equator-S mission, Publishe d in 2001 by John Wiley & Sons, Ltd.