What is the octaweb?

The name describes the shape: eight engines in a ring around one in the centre. Falcon 9 has used it since 2013, replacing an earlier square grid that was harder to build and harder to protect.

Nine smaller engines instead of one large one buys three things. It lets the rocket keep flying if one fails, which a single-engine stage cannot. It allows deep throttling for landing, because engines can be shut down rather than merely turned down. And it means the same engine can be mass-produced for every stage of every booster, which is what makes them cheap.

The layout also matters structurally. Arranging the engines in a ring spreads their thrust into the tank wall evenly, and the frame holding them doubles as the mount the rocket sits on at the pad.

The outer eight gimbal to steer. The centre engine is the one used alone for the landing burn, because its thrust points straight through the middle of the rocket and needs no correction to keep the descent balanced.

Together they produce 7,600 kN at sea level. Individually each Merlin makes 845 kN and weighs 470 kg — the ring is nine of those bolted into one frame.