mass calculation error when computing rocket trajectory

Hello,

I have project, where I am trying to compute the trajectory of a rocket and also compute when to release a smaller rocket. The code works in general and uses Rungekutta. The main issue is computing the fuelconsumtion/remaining fuel mass. The issue seems that the mass resets after some time and I am not sure the fuel consumtion or fuel mass is computed in the correct manner.

Any help is greatly appriciated

[Torsten]

Please hardcode the user inputs to be made to run your code and to reproduce your problem.