Simple Rocketry: Part 1

Hello, everyone. I know rocketry and engineering are only tangentially related to true astronomy, but I wanted to throw it out there as someone else might find it interesting (and it does have relevance to space exploration, most notably NASA's plans to go back to the Moon and out to Mars).

I intend to cover three types of rockets used or considered for use in space propulsion in layman's terms: chemical rockets, nuclear thermal rockets, and the holy-grail-may-not-even-be-possible nuclear salt water rocket.

Part 1: Basic Rocketry and Chemical Rockets

Rockets are, in principle, just about the simplest way of getting around. By now you've at least heard about Newton's 3rd Law of Motion, which states that "for every action, there is an equal and opposite reaction." This is the law of the universe that is responsible for the recoil of a gun, where firing a bullet in one direction causes the gun to fly back in the other.

Well, imagine you're in space. In space, there is no friction, so flapping your arms, rolling around, or trying to walk won't get you anywhere, because there's nothing to push off of. Now imagine that you happen to be holding a reasonably heavy object like a bowling ball. If you throw that bowling ball away from you, you will find that you begin moving in the opposite direction, just like a gun flying back when it fires a bullet. That's because when you push the bowling ball away from you, you're also pushing yourself away from it.

That's all there is to rocketry. Rockets are just a way of pushing very, very hard on a lot of mass (many, many bowling balls in our example) to get going really fast.

Okay, so let's have a look at the first kind of rocket: a chemical rocket (technically a liquid chemical rocket).



There really isn't much to a chemical rocket as long as you don't worry too much about the chemistry. There are only a few simple parts:

1. Fuel Tanks:
The fuel tanks store the fuel for the rocket. In a chemical rocket, this is almost always hydrogen and oxygen. I won't go into the chemistry, but basically hydrogen gives the biggest "bang for your buck" in terms of weight. Because there is no air in space, you also have to bring your own oxygen to burn the hydrogen.

2. Pumps
The pumps are pretty straightforward. They pump fuel from the fuel tanks into the rocket engine so it can be burned just like a water pump pumps water into your house.

3. Valves
The valves in a rocket engine control how much fuel goes into the combustion chamber. The valves act as a "throttle" for the rocket. Less fuel goes in, less power comes out.

4. Combustion Chamber
This is where everything exciting happens. In the combustion chamber, the fuel (hydrogen) is mixed with the "oxidizer" (oxygen), and the whole mixture is lit with a flame or a spark, which creates a huge explosion.

There is a common misconception that explosions are powerful or deadly because of the fire they create. Although you certainly don't want to be in the path of a fireball, the real reason that explosions are powerful is that they create pressure.

When the hydrogen and oxygen explode in the combustion chamber, there is all of a sudden a huge amount of pressure in the chamber that wants to get out in any way that it can. Because the chamber is closed, it has only two ways out: back through the valves and into the fuel tanks, or out the nozzle. Because there is still fuel in the valves going into the tank, all of that pressure is directed out the nozzle.

As the gases leave the nozzle, more fuel is pumped into the combustion chamber by the pumps and let in by the valves, which is then ignited by the fireball, which then expands and leaves the nozzle, so more fuel is pumped in, and so on. This creates the continuous flame you see coming out of the back of the Space Shuttle.

5. Nozzle
The nozzle is where the gases created by the exploding hydrogen-oxygen mixture in the combustion chamber leave the rocket engine. This is where the power of the rocket, called thrust, is produced. Like our bowling ball example, hundreds of pounds of fuel are being forced out of the back of the rocket at more than 4,000 meters per second, which is more than ten times the speed of sound, which pushes against the rocket engine with an equal force, creating acceleration and speed.

That's all there is! Chemical rockets are pretty simple. If you have any questions/clarifications, don't hesitate to leave a comment. In Part 2 I'll talk about nuclear thermal rockets, a new technology that might take us to Mars.

Source: All images from HowStuffWorks.com