Anatomy hub
Starship· guided tour
Hot-Stage Ring
the vented collar
Falcon 9 switches off, waits, then separates. Starship does something bolder: the booster keeps its three centre engines burning while the ship above lights its own engines and pushes off against the booster's exhaust. Nothing is ever coasting, so nothing is wasted.
Purpose
Vented separation ring
When it fires
Still under thrust
Compare
Falcon 9 coasts first
How it works
Falcon 9 switches its engines off, coasts, then separates. Starship stays under thrust the whole time, so nothing is ever just coasting and wasting time.
For the grown-up
The booster throttles to three centre engines while the ship ignites, then separates under thrust. This eliminates the ullage settling problem and the delta-v lost to coasting, at the cost of needing a vented hot-stage adapter ring that can survive direct plume impingement.
SpaceX Starship