|
|
|
||||||||
|
The Science of Rocketry
|
||||||||
|
|
||||||||
|
Basic Laws
All rockets obey the same basic laws. These laws, more specifically, are Newton's
Three laws of motion. These are:
1) A body at rest remains at rest, or a body in a straight-line motion remains in
uniform motion unless acted upon by an external unbalanced force. (Inertia)
2) An object is accelerated when an external unbalanced force acts upon it. The
rate of acceleration is proportional to the mass of the object. (acceleration=Force/mass or Force=mass x acceleration)
3) For every action, their is an equal and opposite reaction.
What do these Laws Mean?
1) Newton's first law shows that the take-off thrust (upward force) must be more than gravity (downward force) or else the rocket will never leave the launch pad.
2) The second law states how much force is needed to lift and accelerate a rocket. The amount of acceleration achieved will equal the amount of unbalance force divided by the mass.
3) The third law is the acting principle of a rocket. When two liquid fuels are mixed or solid fuels burned their is a controlled explosion in the reaction chamber. An explosion is a rapid expansion of heat and gas due to a reaction. These gases are forced out the nozzle in one direction. Since their is an action downward (gases being forced out the nozzle) then their will be an equal reaction upward (a force pushing the rocket into space)
Propellants
There are three different types of rocket propellants; gas, liquid and solid
Gas
Pressurized gas is forced out of a nozzle. Creates a small amount of force and may be dangerous in an oxygen rich enviornment because it has a potentional to exploded therefore is usually used in space for maneuvering where little thrust is needed and the dangers of it igniting are minimal.
Liquid
A fuel (such as Kerosene, hydrazine and UDMH combinations, and hydrogen in liquid form) is combined with an oxidizer (Oxygen, Acids) to create a controlled reaction (a.k.a. explosion) to propell a rocket. May be hazardous because moving parts are necessary but gives more control because you can vary the amount of fuel or oxidizer entering combustion chamber. The fuel and the oxidizer react in an exothermic reaction. A real life example is when you stike a match the oxygen in the air is acting as the oxidizer and reacting with the match producing heat. In this example you need activation energy or the energy needed to start a reaction(the striking of the match) , while in rockets they tend to use substances that can react with little or no activation energy. The performance of a fuel/oxidizer combination can be measured by specific impulse (I). I=Force/ weight or since weight equals mass x gravity I=Force/ (mass x gravity). Specific impulse measure the amount of time over which a given amount of propellant produces the same amount of thrust. When calculating the Force is in pounds generated over a period of time and the weight in pounds of propellant consumed in the same amount of time. So if one pound of propellant Z produces one pound of thrust for .06 seconds thens its specific impulse is .06 seconds. The higher the specific impulse the better the performance.
Solid
A Fuel and an Oxidizer are packed together with the same relative concentration throughout. These are then burned and gases are forced out the nozzle. Safe because their are no moving parts but may be hazardous because once ignited it cannot be shut down. To vary amount of thrust produce vary pact the fuel and oxidizer closer together.
|
||||||||
|
|
||||||||
| page created with Easy Designer |