Warning warning -- you are rapidly drifting into dubious simulation territory. I won't say it is completely without value, but modeling propellant slosh when the engines are only just barely characterized at a couple history-free point samples is just silly.
The engines will be characterized at some point in the near future, through a full static test program out at the ranch. Schedule is not solid yet.
Your control system won't even care much about the changing mass as propellant is depleted. If it works with a couple different masses, it will work sliding between them.
POGO's propellant tankage is far enough off the geometric center, and the mass fraction is high enough, that propellant depletion has a substantial effect on both the system mass and moments of inertia.
I do model changing propellant mass in my simulator, but I don't worry about slosh.
Point taken. I'll calculate the fundamental frequency of the slosh (using the pendulum model) and see how they compare to the lag time in the control system. If the slosh frequency is much longer, then there is no problem from that direction.
-p
"No science without fancy, no art without facts"
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