Firefly vyvija motor Reaven 1: LOX / RP-1 736.1 kN (4ks v 1.stupni /Alpha r.)
Aerojet vyvija motor AR-1 :LOX / RP-1 2200 kN
a asi pre neho nema pouzitie ( a vecsinu nakladov hradila US vlada).
".... the companies made clear that the centerpiece of the agreement was the potential use of the AR1 on Firefly’s Beta rocket, giving Aerojet a customer for the engine while allowing Firefly to increase the performance of the medium-class rocket."
" Beta is now a single-core vehicle with an AR1 engine in its first stage."