The RD-173 engine is an improved modification of the engine RD-170 (and RD-171). The RD-173 used new materials, an advanced design of the turbopump and the injector head. The mass of the engine was reduced.
Chamber pressure and thrust could be increased. Further was worked for the increased reliability of the engine. Descendants of the RD-173 (the engine was not used in original) are the engines RD-172, RD-180 and RD-171M. While the RD-170 (and RD-171) had nozzles which swiveled on only one axis, the RD-171M and RD-180 swivels on two axes. The engine RD-172 was a variant for the Vulkan project. It is probably the pattern for the modern RD-191 and further variants as RD-193, RD-195 and RD-181.

RD-180F, RD-181, RD-193, RD-195 and RD-175
NPO Energomash considered the possibility of construction several new variants of RD-170 family engines. The proposed variants will be marked as:

RD-180F   for Atlas rocket
RD-181      variant for Antares rocket
RD-193      for prospective Soyuz rocket family
RD-195      for proposed MRKS rocket

RD-175      for proposed STK rocket












RD-171                                                            RD-171M

    RD-180                                                                   RD-180F and M (forced)