Thrust must exceed weight for a rocket to climb; as propellant
burns the vehicle gets lighter so it accelerates faster for the
same thrust (the rocket equation). Staging jettisons the empty,
heavy first-stage tank so the lighter second stage can reach
orbital velocity far more efficiently.
Fuel fraction is the share of the rocket's launch mass
that is propellant rather than structure and payload. A higher
fuel fraction means more mass is shed as the engine burns, so the
same thrust produces a bigger acceleration gain by the end of the
burn â the same rocket-equation effect that makes multi-stage
designs so much more efficient than a single heavy stage.
- Throttle â sets how hard the engine fires, controlling thrust and fuel burn rate.
- Separate stage â jettisons the spent, heavy first stage once past low altitude, instantly cutting mass.
- Reset launch â restarts the simulation from the pad with the current settings.
- Fuel fraction â sets how much of the launch mass is propellant, changing how fast the rocket lightens (and accelerates) as it burns fuel.
- Presets â jump to a representative light-payload (high fuel fraction, fast burn-off) or heavy-payload (lower fuel fraction, sluggish burn-off) configuration.
In practice this is why real launchers stage: SpaceX's Falcon 9
separates its first stage a few minutes after liftoff and lets
the much lighter second stage carry the payload the rest of the
way, since dragging the empty first-stage tank to orbit would
waste huge amounts of propellant.