NK-33 and NK-43 are derived from the earlier NK-15 and NK-15V engines, respectively.
The engines are high-pressure, regeneratively cooled staged combustion cycle bipropellant rocket engines, and use oxygen-rich preburners to drive the turbopumps. The turbopumps require subcooled liquid oxygen (LOX) to cool the bearings. These kinds of burners are highly unusual, since their hot, oxygen-rich exhaust tends to attack metal, causing burn-through failures. The United States had not much investigated oxygen-rich combustion technologies until the Integrated Powerhead Demonstrator project in the early 2000s.[5] The Soviets, however, perfected the metallurgy behind this method. The nozzle was constructed from corrugated metal, brazed to an outer and inner lining, giving a simple, light, but strong structure. In addition, since the NK-33 uses subcooled LOX and kerosene, which have similar densities, a single rotating shaft could be used for both turbopumps.[6] Given its longer, heavier nozzle, the NK-43 ratio in vacuum is slightly heavier, with a thrust-to-weight ratio of about 120:1.[7]
The oxygen-rich technology lives on in the RD-170/-171 engines, their RD-180, and recently developed RD-191 derivatives."
#18