Getting to grips with the mathematics of the code.
The two main routines are used to solve the equation set are;
DIVPAG - an IMSL routine used for solving the set of ODE's that drive the ship velocity and other rate dependent quantities.
DLSLRG - a second IMSL routine used for solving a set of linear equations of the form F = m x a
which work like magic - as long as you feed them the right way - out pops the answer!
Still need to check that the ODE solver is not having to deal with varying simulator inputs while it is trying to home in on a solution.