Musk Lists Raptor Engine Parts Removal Checklist

Elon Musk responded to how complex piping in the first generation of Raptor engines was removed or merged in the second and third generations by listing five categories of parts: secondary propellant and purge lines, power and sensor harnesses, sensors, avionics boxes, and main combustion chamber spark igniters. Many bolt flanges have been replaced with welded joints, reducing weight and leak paths, but some parts are now harder to replace individually.

He emphasized that while removing parts is theoretically simple, practical implementation requires multiple iterations to determine alternative paths, and details are not disclosed. The thrust of the Raptor 3 sea-level variant has increased from about 230 tons to about 250 tons, and the vacuum variant from about 258 tons to about 275 tons; the sea-level engine weight has decreased from about 1630 kg to about 1525 kg. Sensors and controllers are integrated into the airframe, the fairing has been removed, and a new ignition scheme has been implemented across all models, saving about one ton of weight per engine for the entire rocket.

The ignition architecture has shifted from main chamber spark plugs to preburner hot gas ignition. This means that ignition is now more sensitive to temperature and propellant timing: if the preburner does not reach the threshold, the entire system may fail to ignite. Flight 13 was automatically aborted due to some booster engines failing to ignite, and two Raptor 3 engines were subsequently replaced. Early flights also experienced rear chamber leaks and self-destruction after communication was interrupted, leading the company to modify fuel lines, propellant temperatures, ventilation, and purging systems.

The Starship 3 version is also undergoing simplification: the engine fairing has been completely removed, CO2 fire suppression has been simplified, the rear chamber cavity has been reduced, and propulsion and avionics are more tightly coupled. The flaps have been changed from dual actuators to single actuators with three motors. The avionics side has about 60 custom units, with a peak electrical power of about 9 megawatts, and includes microgravity liquid level RF sensors. These removals and welding follow the same logic: fewer interfaces, less leakage, and less disassembly.

SpaceX's long-standing design mantra has been "remove parts or processes first; if the proportion that cannot be added back is less than about 10%, it indicates that the removal was not sufficient." The Raptor 1 to 3 has applied this principle to the methane full-flow staged combustion piping. The welding replacing flanges aligns with the stainless steel rocket body approach, and the company has stopped using 301 stainless steel, opting for self-developed alloys instead.

In market mechanisms, the buyer is the engine hours needed for the deployment and reusability of Starlink 3, while the seller is the McGregor production line and Starbase test stand. Funding has shifted from replaceable maintenance parts inventory to a production rhythm of one-time welding and complete replacements. Beneficiaries are those who can reduce the weight of 33 sea-level and vacuum engines together; the pressure bearers are the traditional engine supply chains that still rely on flange replacements on-site. Event-driven factors stem from continuous flight test feedback on the ignition reliability of the third-generation engines and rear chamber leaks.

Additionally, he did not provide the weight in grams and leakage rates for each category of removed parts, nor did he explain how to recover from preburner failures in flight after the spark igniter was removed.

Source: Public Information