Originally Posted by
Obidiah
To my way of thinking if you had rocket gently orbiting and the entire combuster nozzle array were suspended by tensional springs attached to the body of the rocket itself and you fired the engine the whole array would tension forward on its support springs. Thus in turn dragging the body forward with it.
That is correct. But it does not invalidate Newton's 3rd law.
You have to differentiate the external effect of the mass flow leading to the accelleration of the rocket and the mechanical effect inside the rocket. In order to achieve the mass flow you have to accelerate the exhaust flow. this happens in the Nozzle. And acceleration causes an opposing force.
It is simply the result of the static pressure created in the combustion chamber by the expansion of the hot gases that is subsequently converted to dynamic pressure in the Nozzle.