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How Do Rocket Engines Work - SpacePod

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Now today, let's answer the question "What makes a rocket engine work?" To start, let's go over a few of the basics. When it comes to rockets, you generally only have two types that can get you off the Earth, solid and liquid. Once in space, we have many other options, such as solar sails, ion drives, all that fun sci-fi stuff. But today, we're going to be talking about a typical chemical reaction rocket engine. A chemical rocket generally uses a fuel source and an oxidizer. In the case of the Saturn V moon rocket, the fuel was Rocket Propellant 1 or RP-1 and the oxidizer was liquid oxygen or lox. When you combine these two elements, you get a pretty nice boom. But you can use other chemicals to achieve the same thing. The space shuttle used liquid hydrogen as the fuel and liquid oxygen as the oxidizer. Simply combining these two elements, the fuel and the oxidizer is not enough. That would create fire, but not rocket fire. There are three primary things that make up a rocket engine and with it, rocket fire. The combustion chamber, the throat, and the nozzle. The combustion chamber is where we have the fuel and the oxidizer first begin to mix. By having the fuel sources react in the combustion chamber's very specific shape, we're able to create a tremendous amount of pressure moving at low speeds. Now at the other end of the rocket engine we have the nozzle, which has gases moving at very high velocity but low pressure. And the key to the whole rocket engine is the throat. This is where we take the high pressure but slow gases of the combustion chamber and convert them to the low pressure, but very very fast gases that come out of the nozzle. This combustion chamber, throat and nozzle create thrust by the Newtonian principle that to every action there's an equal and opposite reaction. Gases leaving the rocket engine are pushing downward, which in turn forces the vehicle upward, causing it to hopefully lift off the ground. The engine is using the mass and velocity of the fuel as it burns to create thrust. Even though the fuel starts as a liquid and through the combustion turns to gas, the mass of the fuel stays the same. One pound of rocket fuel is still one pound in liquid or gas form. It's the massive acceleration of this transformation from liquid to gas that causes the momentum. Now the actual equation for this is E = MV squared or energy equals mass times velocity squared. Notice that we're multiplying the velocity or the speed of the gases squared times their mass. This means that the faster that the gases can travel, the better. However, counter-intuitively, the lighter the fuel, the better. The reason we want a lighter fuel is that we can make the lighter fuels move faster, a lot faster. So a heavier but slower fuel mixture like kerosene and liquid oxygen won't give us as much energy as a lighter but faster fuel like liquid hydrogen and liquid oxygen. The upper stage of the Saturn V was hydrogen and oxygen and they could, by varying the hydrogen to oxygen ratio, actually increase the efficiency of the engine in flight by making it more hydrogen-rich. We also have to take into account how heavy each fuel will be and what we need to lift to space. If we can take a really light fuel moving at a very high velocity, we end up creating more-efficient rockets. Using the space shuttle as an example, the orbiter itself or just the space plane portion weighs 165,000 pounds empty. The external fuel tank - 78,100 pounds empty, but holds 1.359 million pounds of liquid oxygen and 226,000 pounds of liquid hydrogen. The solid boosters on the side, they're 185,000 pounds empty, but 1.1 million pounds of fuel is held at liftoff. That vehicle, when it's all is said and done will weigh around 4.4 million pounds at liftoff, most of which is fuel to carry that 165,000 pound orbiter to space. That's a lot of fuel. That's how a basic chemical rocket works. Don't forget to check out our other SpacePods for great cosmic news and other informational videos. Now if you like this video, you probably want to also know how a solid motor works too. And don't forget to subscribe to our Youtube channel and get the latest Spacevidcast videos and live shows right on your Youtube home page.

Video Details

Duration: 4 minutes and 50 seconds
Country: United States
Language: English
Producer: Benjamin Higginbotham
Director: Benjamin Higginbotham
Views: 136
Posted by: spacevidcast on Aug 24, 2013

Fundamentally rockets are very simple designs, but incredibly complex to design, build and fly. In this SpacePod we'll take a peek at the basics of how and why a chemical rocket engine works.

Special thanks to space cadet VAXHeadroom for helping flush out

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