Sensitivity Analysis with a Simple Charging Code

Abstract : Computer simulation techniques using codes such as NASCAP have proved very successful in tracking the spacecraft charging problem. Although a full dynamic three-dimensional code is required to model a spacecraft in orbit, simpler codes (eg MATCHG) can do much to clarify the interaction between the environment and a surface. It is difficult to obtain complete data on either the incident particle fluxes or the material properties which determine the various current components. The latter are dependent upon particle energy which is in turn a function of surface potential; therefore the resulting equilibrium and the charging time to attain this potential are controlled by a long list of input parameters. In order to assess the sensitivity of a solution to each of these inputs, a simple code (EQUIPOT) is used to calculate the net current as surface potential is stepped from zero to that required for equilibrium. The required accuracy for all the parameters is then established by successively introducing a delta of 10% on each. This sensitivity analysis is performed on the properties of a shaded kapton patch on a spherical, conducting, sunlit spacecraft subject to an ambient plasma environment which will produce large, negative potentials. Great Britain.