Staging

One button fires your rocket a step at a time. The staging list is where you decide what that button does and in what order, before you ever reach the pad.

Why a rocket needs staging at all

A rocket built of several engines and separators does not know on its own which of them to fire first. Without a plan, pressing the flight's STAGE button with nothing staged fires every engine on the ship at once. That suits the simplest rocket and nothing else: it is wrong for any ship with a spent tank to drop or a chute to save for the way down. The staging list is that plan, built once in the hangar and carried into the flight.

What a stage is

Open Stages in the hangar's top bar and you get an ordered list of stages, numbered from 1. Each stage holds any number of parts, and every part in it does one named thing the moment that stage fires: an engine ignites, a decoupler lets go, a parachute opens. A part goes into a stage by selecting it on the ship and tapping the + on a stage's row, or Add stage to start a new one; − takes it back out.

A stage is not limited to one part. Put an engine and the decoupler under it in the same stage and both fire together: the old stage falls away and the new one lights in the same instant, with no dead moment of coasting between them.

The staging list with two stages: stage one holding Engine, Decoupler and Parachute set to Deploy, stage two holding Parachute set to Cut, and Deploy/Cut buttons above the list. — Stage 1 lights the engine, drops the spent tank and opens the chute. Stage 2, picked here, only cuts it away.

Order matters: the first press of the flight's STAGE button fires stage 1, the next press fires stage 2, and so on down the list. A stage you drag or nudge to a new spot with its ▲ and ▼ buttons moves in the firing order, not just on the screen.

One part, several jobs, several stages

A part that can do more than one thing offers a row of actions above the list. The Parachute offers Deploy and Cut. Whichever action is picked there is what + puts into a stage, so the same chute can sit in an early stage as Parachute · Deploy and a later one as Parachute · Cut: one stage opens it, another throws it away once you are safely down. A part can only sit in one stage per action, so it never fires the same thing twice.

Staging in flight

On the pad, the first stage is armed and everything else waits. Tapping STAGE fires the active stage and arms the next one; the flight screen names which stage is active so you always know what the button will do next. Once the last stage has fired there is nothing left to arm, and the button has nothing more to do.

The flight HUD in the middle of ascent, reading STAGE 2 · ACTIVE beside the STAGE button. — STAGE 2 is now active. The next press fires whatever that stage holds.

A dropped stage keeps flying

Firing a decoupler does not delete whatever comes off. It becomes its own piece with nobody at the controls, still obeying gravity and the air. An engine still burning when its stage is dropped keeps firing until its tank runs dry, so drop a spent stage with its engine already idle or it will chase your ship up through the flame. A piece with no command part of its own is just debris; one that does have a command part can be switched to and flown.