A few basic questions

After much consideration I decided to go with depleting thrust, so that you can do things like this.

//Lay a mine
Missile m = setFireMissile(new Vector(1,0,0));
if(m != null)
	m.setThrust(m.getVelocity().scale(-1));

or this

//thrust towards center for 4 turns
setThrust(getPosition().normalize().scale(-4));

This will allow smaller robots by making the thrust system easier for robot creators to use, while not impacting those who want to change it every turn. If you set a thrust, it replaces the current thrust, just like calling setAhead(-100) replaces the previous setAhead(100) call.