Most rocket engines don't throttle down well. The main reason isn't the turbopumps (although that can also be an issue) but combustion instabilities in the cham

Most rocket engines don't throttle down well. The main reason isn't the turbopumps (although that can also be an issue) but combustion instabilities in the chamber and flow separation in the nozzle. Nasa overview of liquid engine throttling: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100033271.pdf http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2010003...