Lots of articles out about how Orbital Sciences is talking with three vendors for a replacement for the NK-33/AJ26 engine pair currently used on the Antares booster.
An article on SpaceNews notes three vendors and says:
Thompson told investors on April 17 that Orbital is weighing offers from three companies for the Antares first-stage engine. Two are from Russia, including the current supplier, and one is from the United States.
Orbital Sciences Corp.’s contract with startup Stratolaunch Systems on a rocket to be launched from beneath a large aircraft will produce an enhanced version of Orbital’s Antares rocket capable of handling 15-25 percent more payload, depending on the orbit, Orbital Chief Executive David W. Thompson said April 23.
So, current vendor seems to be Kuznetsov and it looks like they are considering reopening NK-33 production.
I assume the other Russian company would have to be whoever makes the RD-180. Asked in a question " How is an RD-180 engine a reasonable replacement for 2 NK-33/AJ-26 engines on Antares? it seems that the RD-180, with slightly higher thrust would likely be used to increase the payload, per my second quote snippet.
Who could be the US company? What RP1-LOX engine is out there, from a US manufacturer, since Orbital does not have time for a new engine development project, if they intend to bid on the second Cargo Resupply contract for NASA. They need engines sooner than that. Knowing Orbital, maybe it is ATK offering a solid booster (Minotaur writ large?)
So what could the three engines be? I guess new build NK-33's made in Russia, RD-180, and some unknown US engine.