What is a rocket?
The rocket is by far the coolest application of Newton’s Third Law. As you all may already know, the law states that for every action, there is an equal and opposite reaction. Some examples of this include throwing something when you are on ice (a classic example portrayed in physics problems), Baymax’s rocket fist, or perhaps even super high-speed exhaust. For the case of rocket propulsion, this can be done with a liquid propulsion system or a solid propulsion system.
Now what is a solid propulsion system?
Let’s say that you mix aluminum powder, ammonium perchlorate, HTPB, etc. to make a solid mixture of rocket propellant.
You will have this ball of propellant.
Let’s say you light the propellant on fire. What would happen?
It would probably explode like this animation right here.
We have no use for an uncontrolled explosion so let’s say you add a liner for insulation, a case, and a forward closure to seal off one side of the case… and you light it on fire. What would happen?
You see that exhaust has been directed towards a single direction, generating thrust for our makeshift rocket.
Now we want to exhaust the case at faster speeds so that we can get more thrust out of our rocket. How do we do this?
Let’s say we add a nozzle that has a converging section that pressurizes the exhaust and shoots it out of the motor with higher velocities and a diverging section in order to generate thrust expanding exhaust to ambient pressure… and you light it on fire.
This is a solid rocket motor in a nutshell. As you can see in this picture, we have all the components that we just talked about. We have the nozzle, forward closure, liner, case, and propellant. You may be asking yourself, why is there a hole in the middle of the propellant? Well, this is one example of a propellant grain, called a BATES grain. There are many more grains that alter the thrust curve of a solid rocket. You can imagine how certain grains have more surface area to burn initially and gradually mellow out over time. We can take advantage of these different grains by stacking them as well.