Marcia Smith, SpacePolicyOnline.com, on comments from VPs of Aerojet Rocketdyne and Dynetics:
If ULA retires Atlas V as planned and chooses BE-4 for Vulcan, AR1 still could be used for other customers, Cook stressed. Among them is NASA, which is currently working on the first two versions of the Space Launch System (SLS) that will be able to launch 70 metric tons (MT) and 105 MT respectively. A 130-MT version is planned for some time in the 2020s and AR1 could be used for that configuration, replacing the solid rocket strap-ons in the current design.
I’ve been asking for a while what AR1 is going to be used for once it’s built. One theory I have is that it could be used for a future, upgraded version of Antares.
If the endgame here is to be used as the engines for the SLS advanced boosters, I would not be surprised in the slightest. The Dynetics VP speaking here about AR1 is Steve Cook, the same one who managed the Ares program. He’s probably got a leg up on what the plans would be, and at this point, it seems like policy that SLS must be powered by Rocketdyne motors—RS-25, RL10, and the baseline for the advanced boosters is the F1-B.
From a technical perspective, you’d need somewhere in the ballpark of seven AR1 engines to match the power of a pair of F1-B engines. From a political perspective, this makes too much sense for how the SLS program is managed.