Rockets

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A rocket is an engine, a fuel tank, steering and fins on a body that stands on its tail. RocketSettings describes it and PhysicsRocket flies it.

There is no sandbox command for rockets yet, and I haven’t tuned the defaults in game.

Frame

A rocket’s nose is the grid’s +Y. Build it standing up. The engine pushes along +Y, and +Z is only the direction “stick forward” tips the nose toward. +X is still the left side.

Flying it

Key	Effect
Jump (Space) held	Opens the throttle at `throttleRate` per second.
V held	Closes it.
W / S	Tips the nose toward +Z / -Z.
A / D	Tips the nose left / right.

The throttle stays where you leave it. With the stick centred, the rocket stands itself back up toward vertical, as fast as it can steer. The engine only runs with a player in the seat, and getting out closes the throttle. Out of fuel it coasts and falls, tumbling if nothing steers it.

Wheels on a rocket are landing legs: they are always braked and take no input.

Fuel

The tank starts full. At full throttle it lasts burnTime seconds, and burns in proportion at less. Set burnTime to 0 for unlimited fuel; fuel() then always reports 1.

GroupVehicle.fuel(share) sets the fuel left, 0 to 1. It is saved with the group (RocketFuel) and carried over when the body is rebuilt. The dashboard shows it as a percentage.

RocketSettings

Thrust is a share of the body’s weight under normal gravity (9.81 m/s²), so a stone rocket flies like a wooden one of the same shape, and the engine still pushes where there is no gravity at all.

Field	Default	Meaning
`thrust`	2	Thrust at full throttle as a share of the weight. Above 1 it lifts off.
`burnTime`	60	Seconds of fuel at full throttle. 0 never runs out.
`terminalSpeed`	90	m/s at which air drag equals the weight, so a falling rocket tops out near it.
`steerRate`	0.8	rad/s of tilt at full stick from the engine’s gimbal at full throttle; in proportion at less, none with the engine off.
`rcsRate`	0.3	rad/s from steering thrusters that work with the engine off. 0 for none.
`stability`	1.5	How fast (1/s) the fins turn the nose into the airflow. 0 for no fins.
`finSpeed`	40	m/s at which fins reach full effect. Slower, they fade with the square of the speed.
`upright`	0.5	How fast (1/s) it stands back up with the stick centred, while it can steer. 0 for none.
`attitudeResponse`	4	How fast (1/s) the body’s spin follows what steering and fins ask.
`throttleRate`	0.5	Share of full throttle per second the keys move it.
`stickRate`	3	Share of full travel per second the stick follows the keys. 0 follows at once.

How it works

Each tick:

The throttle moves with the keys and fuel drains by throttle × dt / burnTime.
While burning, the rocket is kept awake. A rocket sitting on the pad barely moves, and Jolt would otherwise put it to sleep in the middle of a burn.
Thrust along the nose: thrust × mass × 9.81 × throttle.
Drag against the motion: weight × (speed / terminalSpeed)², never more than stops it in a step. Below 0.5 m/s there is none.
Steering. The steering rate is steerRate × throttle + rcsRate. The stick asks for that spin about the body’s left (pitch) and forward (roll) axes. Spin about the nose itself is held at zero.
Fins add a turn toward the direction of motion, stability × min(1, (speed / finSpeed)²).
Upright. With the stick centred and some steering available, a turn toward world up is added at min(upright, steering rate).
The result is blended onto the body’s spin at attitudeResponse times how much control it has (engine, thrusters and fins together, at most 1). With no gimbal, no thrusters and no airflow, nothing steers it.

PhysicsRocket

Method	Notes
`control(throttle, pitch, right)`	Throttle up +1 / down -1 while held; stick in [-1, 1]. Wakes the body.
`setEngine(boolean)`	Off closes the throttle.
`step()`	Once a tick before the physics step.
`burning()`	Engine on, throttle open and fuel left (or unlimited). For the flame and sound.
`speed()`	m/s along the nose.
`climbRate()`	m/s up, against gravity.
`throttle()`	0 to 1.
`fuel()`, `setFuel(f)`	0 to 1.
`pitch()`, `roll()`	The stick as eased.
`body()`, `settings()`, `isDestroyed()`