[18] Raptor is designed for extreme reliability, aiming to support the airline-level safety required by the point-to-point Earth transportation market.

[19] Gwynne Shotwell claimed that Raptor would be able to deliver "long life... and more benign turbine environments".

FFSC is a departure from the more common "open-cycle" gas generator system and LOX/kerosene propellants used by its predecessor Merlin.

Both oxidizer and fuel streams are converted completely to the gas phase before they enter the combustion chamber.

Raptor 2's main combustion chamber uses an undisclosed ignition method that is allegedly less complex, lighter, cheaper, and more reliable than Merlin's.

Specific impulse is increased, and the risk of cavitation at inputs to the turbopumps is reduced due to the higher propellant fuel mass flow rate per unit of power generated.

[21] Cavitation (bubbles) reduces fuel flow/pressure and can starve the engine, while eroding turbine blades.

Liquid methane and oxygen propellants have been adopted by many companies, such as Blue Origin with its BE-4 engine, as well as Chinese startup Space Epoch's Longyun-70.

[33] Many components of early Raptor prototypes were manufactured using 3D printing, including turbopumps and injectors, increasing the speed of development and testing.

[21] In 2019, engine manifolds were cast from SpaceX's in-house developed SX300 Inconel superalloy, later changed to SX500.

[35] SpaceX's Merlin and Kestrel rocket engines use a RP-1 and liquid oxygen ("kerolox") combination.

[39] In November 2012, Musk announced that SpaceX was working on methane-fueled rocket engines, that Raptor would be methane-based,[40] and that methane would fuel Mars colonization.

[53] Initial development testing[54] of Raptor components was done at NASA's Stennis Space Center,[17][55] beginning in April 2014.

Multiple engines were out before the flight termination system (FTS) destroyed the booster and ship.

[64] In November 2016, Raptor was projected to power the proposed Interplanetary Transport System (ITS), in the early 2020s.

[21] Musk discussed two engines: a sea-level variant (expansion ratio 40:1) with thrust of 3,050 kN (690,000 lbf) at sea level for the first stage/booster, and a vacuum variant (expansion ratio 200:1) with thrust of 3,285 kN (738,000 lbf) in space.

[67] The redesign was aimed at Earth-orbit and cislunar missions so that the new system might pay for itself, in part, through economic spaceflight activities in the near-Earth space zone.

[69][21] By mid-2018, SpaceX was publicly stating that the sea-level Raptor was expected to have 1,700 kN (380,000 lbf) thrust at sea level with a specific impulse of 330 s (3,200 m/s), with a nozzle exit diameter of 1.3 m (4.3 ft).

[...] approximately a 200 (metric) tons engine aiming for roughly 300 bar chamber pressure.

[47][71] Engine testing was planned for NASA's Stennis Space Center in Mississippi under US Air Force supervision.

[47] In October 2017 USAF awarded a US$40.8 million modification contract for a Raptor prototype for the Evolved Expendable Launch Vehicle program.

Each version of the engine has a corresponding Raptor Vacuum (RVac) variant[78] with an extended, regeneratively-cooled nozzle for higher specific impulse in space.

[82] By November 2022, SpaceX produced more than one Raptor a day and had created a stockpile for future launches.

[86] The reduction in externally visible components was so extreme that initial pictures were accused of being incomplete.

[89]: 42:19–45:50 In October 2021, SpaceX initiated an effort to develop a conceptual design for a new rocket engine with the goal of keeping cost below US$1,000 per ton of thrust.

[83] Although the initial design effort was halted in late 2021, the project helped define an ideal engine, and likely generated ideas that were incorporated into Raptor 3.

"[83] In June 2024, the LEET concept was clarified as a total tearup of the Raptor 3 design, with Musk stating that SpaceX will "probably do that at some point.