Took a bit of searching but I found it again. https://www.aacademica.org/hernan.emilio.tacca/9.pdf https://www.aacademica.org/hernan.emilio.tacca/9.pdf If I r

Took a bit of searching but I found it again. https://www.aacademica.org/hernan.emilio.tacca/9.pdf https://www.aacademica.org/hernan.emilio.tacca/9.pdf If I remember correctly simple turbo pump feed engines have to run using a lot of excess fuel. Simple designs just dump the turbine exhaust overboard. That represents a fair amount of wasted energy. Advanced designs feed the exhaust back into the engine. I think they also scavenge some energy from cooling the nozzle.