BUILD · FALCON 9 · THE ENGINE ROOM
Nine Merlin engines — eight around one — each sealed in its own structural bay, so that a failure stays the failure of one engine.
This is the real engine section, built part by part. Rotate it. Pull the Explode slider to separate the nine engines — then click one Merlin and explode it again into its combustion chamber, turbopump, pintle injector and bell nozzle. Switch to Materials to see the Inconel, titanium and aluminium the real hardware is made of. Then shut an engine down and watch what happens.
Explode it, inspect any part, then break it — shut down an engine and the other eight compensate, exactly as Falcon 9 did on CRS-1.
NASA describes each engine as “housed within its own metal bay to isolate it from neighboring engines.” That isolation is why engine-out capability is a structuralclaim, not just a software one — a failed engine can't take its neighbours with it.
On CRS-1 (October 2012), Falcon 9 lost engine 1 at T+79 seconds. The flight computer throttled up the remaining eight and burned them longer — and still delivered Dragon to the International Space Station.
Each engine is a gas-generator-cycle Merlin 1D: a turbopump feeding a regeneratively-cooled chamber, a single central pintle injector (Apollo-lunar-module heritage), and a 16:1 expansion bell — steered by two thrust-vector actuators.
Sources: NASA — Meet the Octaweb; SpaceX Falcon User's Guide (Rev 8, May 2025). Engine geometry is modelled to the Falcon 9's published 3.66 m diameter; SpaceX publishes no engine drawings, so proportions are indicative.
You've seen the engines — now assemble the entire Falcon 9, stage by stage.