Backward Orbit Propagation using simulink

Hi everyone,

In the frame of a university project I am actually running several orbit propagations using a rather complex propagator developed using Simulink (it includes J2,3.. effects, third body perturbation, solar radiation pressure effects etc.. ).

Now for some reason I need to perform backward propagation: given the state of the body at an initial time t0 I need the position and velocity at t0-Dt. I have no idea how to achieve this because Simulink doesn't allow to directly run backward integration in time.

I know from a previous post that a possible solution would be to recast the system of equations in order to account for "negative time", but I don't find this solution to be feasible due to the complexity of the simulink model.

Any advice or suggestion(?) will be appreciated,

Thanks in advance,

AF.