Simply, I am working on my physics thesis and I need to observe the effects of gradual change in mass of a rocket in orbit without any force being applied, namely thrust. For this I need fuel consumption, the rate of which I can modify but no thrust. The only thing that comes to my mind is using a 0 Isp engine but I don't know how to change the files. Do you have any suggestions other than a modified engine? If not, how do I change the Isp and thrust values of engines in the game? Is there a mod I can use?