What Is a Rocket?
Do-It-Yourself Podcast Rocket Science Videos Transcript
(Curry) A rocket is a launch vehicle. It can also be a space capsule, usually in the form of a cylinder or a tubelike structure that launches from the Earth. And it can be used to carry humans into space. It can also be used to carry supplies such as cargo, food, materials or anything that can be carried to the International Space Station (because we do have astronauts that live on the space station, and they need supplies and everything to live and to work up there.) It can also be used as something to launch satellites into the orbit that the military may use or that NASA may use, or it can even be a satellite.
The Parts of a Rocket
(Curry) All rockets need to have some form of a body or structure to house all the components of it. And most of them are usually in the shape of a tube or a cylinderlike structure. They also need to have a form of a propellant system, which is the fuel system that ignites and produces thrust to get it off the ground. They also need to have aerodynamic components, which are components of the rocket such as a nose cone or fins or wings. It needs to have all of those to be able to make sure that it gets to its desired target in the most efficient and quickest way possible.
What Is a Propellant System?
(Curry) [The] propellant system ... is one the most important parts of the rocket. That's going to house your fuel system, your engines, and it's going to produce ... thrust and ... velocity to actually get off the ground.
The Rocket's Body
(Curry) First of all, you have (the) body of your rocket, which is your main structure, and it's going to be used to house all the components of the rocket. And it's going to carry your cargo, if you're going to use it for cargo. It's going to carry ... humans, if you're intending to carry humans into space. It's going to house all the wires and the computer system and everything. It's going to be your main structure of the rocket.
The Nose Cone
(Curry) [The] nose cone is going to function as a part of the rocket that is going to reduce your air resistance. An example of that is if you're in a swimming pool and you're swimming across the top of it, and you move your hand across the top of it. You're going to incur a lot of resistance from the water. Which if a rocket had a nose cone on top of it built like this, it would incur a lot of air resistance. But if you move your hand through the water like this, you hardly incur any resistance at all. So a nose cone on the rocket is made to reduce air resistance. Because if you have high air resistance on the front of your rocket, you're going to have to have larger engines and more power to get it to where it's intended to go.
(Curry) The fins help maintain the stability of the rocket as it flies. If you don't have any fins, it's liable to bobble and everything as it flies through the air, So (the fins are) definitely going to help reach its intended target.
What Is Thrust?
(Curry) Thrust is actually the force that gets you off the ground that is produced from the fuels mixing in the engine and combusting and flowing out the nozzle out a high velocity. And that force that pushes back down on the ground is the thrust that you need for the rocket to actually get off the ground and launch into orbit.
Gravity and Rockets
(Curry) You're always going to try to overcome gravity to move against that force that is holding us down on the Earth.
(Curry) Isaac Newton came up with three laws of motion. The first one is that an object will remain at rest unless acted on by an outside force. The second one is force equals mass times acceleration. And then the third one is for every action, there is an equal and opposite reaction.
Newton's First Law
(Curry) With the first one, an object such as a rocket will remain on the Earth until acted on by an outside force, such as the force from the engines that are going to push it off of the Earth.
Newton's Second Law
(Curry) For force equals mass times acceleration, you need to calculate the amount of force that’s needed to accelerate the rocket off of the Earth's surface also due to its mass.
Newton's Third Law
(Curry) Then for the third one, for every action there is an equal and opposite reaction. The forces are going to equal out that it's going to need to lift the rocket off the Earth compared to the amount of thrust that's needed. So as the rocket launches, the amount of thrust that's pushing down on the Earth is what is going to be pushing back up, up under it to get it off the Earth's surface.
(Curry) Don't ever go out and build a model rocket or paper rocket and especially (don't) launch it without an adult present, such as a teacher, a parent or an older sibling, there to help you out to make sure that you are following all the safety procedures that need to be followed.
Where to Launch
(Curry) Consider the environment that you are going to be launching it in. If you're going to have a rocket that is intended to go extremely far ... probably wouldn't be the best thing to launch it in your neighborhood. Go out to an open field or something that is far away from other people or anything that it can endanger once it falls back to Earth.
Materials for Rockets
(Curry) Consider the materials that you are going to use. If you are going to use an engine that ignites, it probably wouldn't be a good idea to have a lot of paper components on the rocket such as your body, your wings, your nose cone or your fins because your rocket won't go very far because it could also, as soon as it ignites, catch on fire.
(Curry) Always remember to keep weight at a minimum. You're always going to get to go a lot further if you're carrying less weight. So always try to research a way to decrease the amount of weight that your rocket is going to carry.
Building a Stable Rocket
(Kepner) I am here to teach you about the stability of a rocket, which relies on two factors: the center of pressure and the center of gravity.
(The) first one we're going to calculate is the center of gravity. This is a basic rocket Alpha III from Estes, and to determine the center of gravity we can do that in one very easy step. First of all, I would like to point out that the rocket should be ready for flight when you determine the center of gravity. So you want to make sure that the motor is in there. The weight of the motor is going to affect the center of gravity, and the parachute and all the internals are installed.
To find the center of gravity, all you need to do is take the rocket and balance it on one finger. And wherever the rocket will balance and stay is your center of gravity. On our rocket, it is approximately right here. We are going to mark that with a sticker. That is our center of gravity. Mark that as CG and an X.
The center of pressure is a little bit harder concept to understand, but the center of pressure is the relationship between the drag on the rocket, mainly on the nose cone, and the drag on the fins of the rocket. If you think about a rocket flying through the air, the majority of the aerodynamics, the majority of the wind and air is going to be felt on the nose cone of the rocket and on the fins of the rocket. So the center of pressure is going to be somewhere between the two.
The larger the fins, the more it is going to be pushed back. The smaller the fins, the more it is going to be towards the front. Now the center of pressure is really difficult to calculate accurately, but there is a very simple method that I am going to show you.
The simple method involves taking the rocket and putting it on a piece of cardboard, then actually tracing the shape of the rocket on the cardboard. Once you do that, you should end up with something that looks kind of like your rocket. What we are going to do is actually take this drawing and cut it out. So you should need a pair of scissors. You will end up with a two-dimensional rough copy of your rocket.
The way to determine the center of pressure is actually the same method we did for the center of gravity, except now we have a two-dimensional rocket and we are going to balance that on our finger. And that point is our center of pressure, CP. We can compare that with our rocket and determine that the center of pressure is slightly in front of the center of gravity. That's exactly what you want in a stable rocket.
A good rocket will have the center of pressure slightly in front of the center of gravity.
You want to have that center of pressure exactly one to two body diameters in front of the center of gravity. So this rocket is one inch in diameter, which means the center of pressure should be somewhere between one and two inches in front of the center of gravity.
This particular rocket, the way we measured it, is about three quarters of an inch. So it is slightly unstable. But again, this method for the center of pressure is not very accurate.
The best method would be to use a computer program and calculate it. As you see, we've got center of gravity behind the center of pressure. The center of pressure is about three quarters of an inch. So that is going to be a stable rocket.
The reason you want a stable rocket is because if the rocket's unstable it will not fly straight. And it is actually bad for a rocket to be too stable. If we were to make these fins extremely large, say as big as this, then we're going to a rocket that is very, very stable. The problem with that is the rocket won’t go straight when there is any kind of wind. Because as the rocket's going up, the wind is going to push against the fins and cause the rocket to turn and go about 90 degrees off to the side. So stability-wise, to determine the stability of a rocket you need to calculate the center of gravity and the center of pressure.
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