Pratt & Whitney Rocketdyne and Dynetics, with a booster design known as "Pyrios", which would use two F-1B engines derived from the F-1 LOX/RP-1 engine that powered the first stage of the Saturn V vehicle in the Apollo program. In 2012, it was determined that if the dual-engined Pyrios booster was selected for the SLS Block II, the payload could be 150 metric tons (t) to Low Earth Orbit, 20 t more than the baseline 130 t to LEO for SLS Block II.[38] In 2013, it was reported that in comparison to the F-1 engine that it is derived from, the F-1B engine is to have improved efficiency, be more cost effective and have fewer engine parts.[39] Each F-1B is to produce 1,800,000 lbf (8.0 MN) of thrust at sea level, an increase over the 1,550,000 lbf (6.9 MN) of thrust of the initial F-1 engine.[40]
ATK proposed an advanced SRB named "Dark Knight" with more energetic propellant, a lighter composite case, and other design improvements to reduce costs and improve performance. ATK states it provides "capability for the SLS to achieve 130 t payload with significant margin" when combined with a Block II core stage containing five RS-25 engines. However, the advanced SRB would achieve no more than 113 t to low earth orbit with the current core stage with four RS-25 engines.[3][38][41]
Christopher Crumbly, manager of NASA’s SLS advanced development office in January 2013 commented on the booster competition, "The F-1 has great advantages because it is a gas generator and has a very simple cycle. The oxygen-rich staged combustion cycle [Aerojet’s engine] has great advantages because it has a higher specific impulse. The Russians have been flying ox[ygen]-rich for a long time. Either one can work. The solids [of ATK] can work."[42]
I guess you could just change a mesh? and have cfg for different boosters. Any one for that? Not sure what the booster mesh would look like?