Ship.js

class Ship extends SpaceObject {
	// Degrees per second
	var turnRate:float = 90;
	
	// velocity change per second
	var thrustForce:float = 200;
	
	var thrusterPos:Vector3 = Vector3.zero;
	var thrusterPrefab:GameObject;
	private var thrusterParticleEmitter:ParticleEmitter;
	private var thrusterPeakEmission:float;
	
	
	// Init
	virtual function Start() {
		super.Start();
		
		var thrusterObject:GameObject = Instantiate(thrusterPrefab, Vector3.zero, Quaternion.identity);
		thrusterObject.transform.parent = this.transform;
		thrusterObject.transform.localPosition = thrusterPos;
		
		thrusterParticleEmitter = thrusterObject.particleEmitter;
		thrusterPeakEmission = thrusterParticleEmitter.maxEmission;
	}
	
	
	// Updates
	virtual function Update () {
		super.Update();
		
		UpdateThruster();
	}
	
	virtual function UpdateRotation() {
		super.UpdateRotation();
		
		transform.Rotate(0, turnRate * Input.GetAxis("Horizontal") * Time.deltaTime, 0);
	}
	
	virtual function UpdateAccel() {
		super.UpdateAccel();
		
		accel = transform.forward * thrustForce * Input.GetAxis("Vertical");
	}
	
	virtual function UpdateThruster() {
		var isForwardThrust = (accel.normalized - transform.forward).magnitude < 0.1;
		thrusterParticleEmitter.emit = accel.magnitude > 0 && isForwardThrust;
		
		var emission:float = accel.magnitude/thrustForce * thrusterPeakEmission;
		thrusterParticleEmitter.minEmission = emission;
		thrusterParticleEmitter.maxEmission = emission;
	}
	
	
	
	
	
	// Editor
	function OnDrawGizmosSelected() {
	    Gizmos.color = Color.yellow;
	    
	    var localThrusterPos:Vector3 = transform.position + Vector3.Scale(thrusterPos, transform.localScale);
    	    Gizmos.DrawWireCube(localThrusterPos, Vector3(1,1,1));
	}
}

SpaceObject.js

class SpaceObject extends MonoBehaviour {
	
	var mass:float = 1;
	var maxSpeed:float = 200;
	
	protected var accel:Vector3 = Vector3.zero;
	protected var vel:Vector3   = Vector3.zero;
	
	virtual function Start() {
		// Stub
	}
	
	virtual function Update () {
		UpdateRotation();
		UpdateAccel();
		UpdateVel();
		UpdatePos();
	}
	
	virtual function UpdateRotation() {
		// Stub
	}
	
	virtual function UpdateAccel() {
		// Stub
	}
	
	virtual function UpdateVel() {
		vel += accel * Time.deltaTime;
		
		if (vel.magnitude > maxSpeed) {
			vel *= maxSpeed / vel.magnitude;
		}
	}
	
	virtual function UpdatePos() {
		transform.position += vel * Time.deltaTime;
	}
	
}