In case you havent seen it, here is the video called "The Engine That Came In From the Cold". The old NK-15 replacement, the NK-33 to be used on the newer version of the Soviet N-1 Moon rocket, of which 20 NK-33's were slightly altered and renamed the AJ-26.
It's too bad the AJ-26 had that failure back in 2014 during the ORB-3 CRS Cygnus/Antares-100 mission out of Wallops. 2 AJ-26's running at 108% output 734,000lb(f) at sea level and 814,000 lb(F) in vacuum. The 2 Russian RD-191 engines which are named RD-181 for Export to the USA have the advantage of an extra 100,000lb(f) over the NK-33/AJ-26 engines. This extra thrust caused Orbital to drop the Antares 100 series rocket, concentrate on the Antares 200 series rocket with the new RD-181 engines and Enhanced Cygnus cargo vehicle. Due to the fact that the Antares 200 series rocket was designed fot AJ-26 thrust levels, the new RD-181s will run underthrottled. Then once the upgraded Antares-300 series rocket comes on line, the RD-181 will be able to be run at full thrust.
Orbital/ATK was going to re-engine and update the Antares rocket, but instead of 2018 or so, they moved it up to 2016. The accident merely sped up the upgrading.
ORB-OA4 with a Cygnus atop a ULA Atlas 5 launcher was successful, OA-5 and OA-7 will fly atop the new Antares 230 with the newer RD-181 engines and OA-6 will ride up on 2nd ULA Atlas 5. The reason for the 2nd Atlas 5 launcher is that with the 2nd Atlas rocket Orbital Sciences can use the extra upmass capability to complete its payload/upmass to ISS in 3 more(2 Antares 230's and 1 Atlas-5 for missions OA6, OA-5 and OA-7)missions rather than 4 more missions using its own Antares rockets.
At least Wallops in now launching again, and the upgraded Antares 200 with 2 RD-181's(down throttled) along with the Enhanced Cygnus vehicle and the upgraded Castor XL 2nd stage. Whenever an enhanced Cygnus vehicle is launched, a Castor XL 2nd stage must be used. The Castor XL 2nd stage was launched (for the 1st time) with a Standard Cygnus in October 2014 when the 1st stage had an issue and eploded 6 seconds after liftoff.
NK-33 AJ-26 video
Orb-3 explosion and fall back to pad, this was the 5th flight of Antares
view from camera at the pad The solid propellant from the CASTOR=XL upperstage burned quite hot for many minutes after the RUD(Rapid Unepected Disassembly)