These were attached to the Energia core rather than the orbiter, so were not recoverable after a flight, but created a more modular design (the Energia core could be used for a variety of missions besides launching the shuttle).
Mesin tersebut melekat pada pengorbit Energia Core, sehingga tidak dapat dipulihkan setelah penerbangan, tetapi menciptakan desain yang lebih modular (Energia Core dapat digunakan untuk berbagai misi selain meluncurkan pesawat ulang-alik).