: An upgraded variant of the 1A with a more powerful turbine; it was never used on a flight vehicle before SpaceX shifted to regenerative cooling.

: Based on the Apollo Lunar Module landing engine, this provides excellent stability and allows for deep throttling.

: The current active version, introduced in 2013. It is designed for rapid reusability and vertical landings. Core Specifications (Merlin 1D) Sea Level (SL) Vacuum (Vac) Thrust ~845 kN (190,000 lbf) ~981 kN (220,500 lbf) Specific Impulse (Isp) Chamber Pressure 9.7 MPa (1,410 psi) 9.7 MPa (1,410 psi) Thrust-to-Weight Ratio Sources: Design Innovations

: The first to feature a regeneratively cooled nozzle and combustion chamber. It powered the first privately developed rocket to reach orbit (Falcon 1 Flight 4) and early Falcon 9 flights.

: Uses a triple-redundant flight computer system on each engine to ensure high reliability during launch.