SpaceX rocket engines

Since the founding of SpaceX in 2002, the company has developed four families of rocket engines — Merlin, Kestrel, Draco and SuperDraco — and since 2016 developed the Raptor methane rocket engine and after 2020, a line of methalox thrusters.

In the first ten years of SpaceX, led by engineer Tom Mueller, the company developed a variety of liquid-propellant rocket engines, with at least one more of that type under development. As of October 2012^[update], each of the engines developed to date—Kestrel, Merlin 1, Draco and Super Draco—had been developed for initial use in the SpaceX launch vehicles—Falcon 1, Falcon 9, and Falcon Heavy—or for the Dragon capsule. Each main engine developed by 2012 has been Kerosene-based, using RP-1 as the fuel with liquid oxygen (LOX) as the oxidizer, while the RCS control thruster engines have used storable hypergolic propellants.

In November 2012, at a meeting of the Royal Aeronautical Society in London, United Kingdom, SpaceX announced that they planned to develop methane-based engines for their future rockets. These engines would use staged cycle combustion, for higher efficiency similar to the system used on the former Soviet Union's NK-33 engine.^{[needs update]}

By mid-2015, SpaceX had developed a total of 9 rocket engines architectures in the first 13 years of the company's existence.

SpaceX has developed two kerosene-based engines through 2013, the Merlin 1 and Kestrel, and has publicly discussed a much larger concept engine high-level design named Merlin 2. Merlin 1 powered the first stage of the Falcon 1 launch vehicle and is used both on the first and second stages of the Falcon 9 and Falcon Heavy launch vehicles. The Falcon 1 second stage was powered by a Kestrel engine.

Merlin 1 is a family of LOX/RP-1 rocket engines developed 2003–2012. Merlin 1A and Merlin 1B utilized an ablatively-cooled carbon-fiber composite nozzle. Merlin 1A produced 340 kilonewtons (76,000 lb_f) of thrust and was used to power the first stage of the first two Falcon 1 flights in 2006 and 2007. Merlin 1B had a somewhat more powerful turbo-pump, and generated more thrust, but was never flown on a flight vehicle before SpaceX's move to the Merlin 1C.

The Merlin 1C was the first in the family to use a regeneratively-cooled nozzle and combustion chamber. It was first fired with a full mission duty firing in 2007, first flew on the third Falcon 1 mission in August 2008, powered the "first privately-developed liquid-fueled rocket to successfully reach orbit" (Falcon 1 Flight 4) in September 2008, and subsequently powered the first five Falcon 9 flights — each flown with a version 1.0 Falcon 9 launch vehicle — from 2010 through 2013.

The Merlin 1D, developed in 2011–2012 also has a regeneratively-cooled nozzle and combustion chamber. It has a vacuum thrust of 690 kN (155,000 lbf), a vacuum specific impulse (I_sp) of 310 s, an increased expansion ratio of 16 (as opposed to the previous 14.5 of the Merlin 1C) and chamber pressure of 9.7 MPa (1,410 psi). A new feature for the engine is the ability to throttle from 100% to 70%. The engine's 150:1 thrust-to-weight ratio is the highest ever achieved for a rocket engine. The first flight of the Merlin 1D engine was also the maiden Falcon 9 v1.1 flight. On September 29, 2013, the Falcon 9 Flight 6 mission successfully launched the Canadian Space Agency's CASSIOPE satellite into polar orbit, and proved that the Merlin 1D could be restarted to control the first stage's re-entry back into the atmosphere—part of the SpaceX reusable launch system flight test program—a necessary step in making the rocket reusable.