The Csat parameter determines how long it takes for the simulation to reach equilibrium. I am not sure if my current setting for Csat is correct, and I would like to use a more realistic value to accurately simulate the process of potential change on the surface of the spacecraft. I am currently mimicking the charging effects of a spacecraft with a surface area of 96 square meters in a NASA worst GEO orbital environment. Assuming a parallel-plate capacitor between the spacecraft and the ground potential of the space plasma environment, Csat = ε0*96/760, where ε0 denotes the vacuum dielectric constant, 96 is the surface area of my spacecraft, and 760 is the length of the débay (roughly). This works out to be about 1pF for Csat, but this seems a bit too small to the point where the potential changes very drastically. After all, in the NASA worst GEO simulation case Csat is set to 1μF. I’m wondering if I’m estimating Csat in this way correctly? If not, how should I estimate it?
Hi Yongshan Ba. You can allow SPIS to estimate Csat, and guarantee a realistic charging timescales, but it will slow down the simulation; just set “exactCSat” to a value above 0 (e.g. 1). However my suggestion is just to run SPIS for a brief moment until you see no real evolution in the CSat value, and then restart the simulation with that value (and exactCSat = 0)
Here’s the text on the calculation I got from SPIS documentation, but there’s probably more to it:
More precisely Gauss theorem (integral Poisson equation) is used at each time step to determine the SC potential so as to insure exact charge conservation (a variable Csat is derived from that)|
Thanks for your reply! I actually noticed exactCsat a long time ago, but hadn’t looked closely at its use, so perhaps I should take a fresh and careful look at the manual.