Rocket, self-propelled device that carries its own fuel, as well as the oxygen, or other chemical agent, needed to burn its fuel. Most rockets move by burning their fuel and expelling the hot exhaust gases that result. The force of these hot gases shooting out in one direction causes the rocket to move in the opposite direction. A rocket engine is the most powerful engine for its weight. Other forms of propulsion, such as jet-powered and propeller-driven engines, cannot match its power. Rockets can operate in space, because they carry their own oxygen for burning their fuel. Rockets are presently the only vehicles that can launch into and move around in space.
A rocket can be as simple and small as a firework, which has a small amount of thrust, or as complex and powerful as the Saturn V rocket, which took humans to the Moon. British Congreve war rockets, which were used in the War of 1812, are referred to in a line of the United States national anthem: “And the rockets red glare…” Rockets have many applications both on Earth and in space. The most common and well-known use of rockets is for missiles—weapons that deliver explosive warheads through the air to specified targets. Rockets also have numerous peaceful purposes. Upper atmospheric research rockets, or sounding rockets, carry scientific instruments to high altitudes, helping scientists carry out astronomical research and learn more about the nature of the atmosphere. Jet-Assisted-Take-Off (JATO) rockets help lift heavily loaded planes from runways. Lifesaving rockets carry lifeline ropes to ships stranded offshore. Ships in distress can launch signal rockets to signal for help. Rocket ejection seats safely boost pilots out of jet planes during emergencies. Fireworks have provided entertainment for centuries, and model rockets form the basis of a popular hobby.
Monday, March 3, 2008
HISTORY
According to the writings of the Roman Aulus Gellius, in 400 BC, a Greek Pythagorean named Archytas, propelled a wooden bird using steam. However, the only knowledge that exists of it, is in Aulus's writings, from 5 centuries later, no diagrams survive, and whether it was truly propelled by rocket power is unknown.
The availability of black powder to propel projectiles was a precursor to the development of the first solid rocket. Ninth Century Chinese Taoist alchemists discovered black powder in a search for the Elixir of life; this accidental discovery led to experiments in forms of weapons like bombs, cannon, incendiary fire arrows and rocket-propelled fire arrows.
Exactly when the first flights of rockets occurred is contested, some say that the first recorded use of a rocket in battle was by the Chinese in 1232 against the Mongol hordes. Reports were of fire arrows and 'iron pots' that could be heard for 5 leagues - 15 miles - and that, upon impact, exploded causing devastation for 2,000 feet in all directions, apparently due to shrapnel. The lowering of iron pots may have been a way for a besieged army to blow up invaders. The fire arrows were either arrows with explosives attached, or arrows propelled by gunpowder, such as the Korean Hwacha.
Less controversially, one of the earliest devices recorded that used internal-combustion rocket propulsion was the 'ground-rat,' a type of firework, recorded in 1264 as having frightened the Empress-Mother Kung Sheng at a feast held in her honor by her son the Emperor Lizong.
Subsequently, one of the earliest texts to mention the use of rockets was the Huolongjing, written by the Chinese artillery officer Jiao Yu in the mid 14th century; this text also mentioned the use of the first known multistage rocket; this was the 'fire-dragon issuing from the water' (huo long chu shui), used mostly by the Chinese navy. That southern China and Laotian community rocket festivals might then have been key in the spread of rocketry in the Orient was proposed by Frank H. Winter in The Proceedings of the Twentieth and Twenty-First History Symposia of the International Academy of Astronautics.
The availability of black powder to propel projectiles was a precursor to the development of the first solid rocket. Ninth Century Chinese Taoist alchemists discovered black powder in a search for the Elixir of life; this accidental discovery led to experiments in forms of weapons like bombs, cannon, incendiary fire arrows and rocket-propelled fire arrows.
Exactly when the first flights of rockets occurred is contested, some say that the first recorded use of a rocket in battle was by the Chinese in 1232 against the Mongol hordes. Reports were of fire arrows and 'iron pots' that could be heard for 5 leagues - 15 miles - and that, upon impact, exploded causing devastation for 2,000 feet in all directions, apparently due to shrapnel. The lowering of iron pots may have been a way for a besieged army to blow up invaders. The fire arrows were either arrows with explosives attached, or arrows propelled by gunpowder, such as the Korean Hwacha.
Less controversially, one of the earliest devices recorded that used internal-combustion rocket propulsion was the 'ground-rat,' a type of firework, recorded in 1264 as having frightened the Empress-Mother Kung Sheng at a feast held in her honor by her son the Emperor Lizong.
Subsequently, one of the earliest texts to mention the use of rockets was the Huolongjing, written by the Chinese artillery officer Jiao Yu in the mid 14th century; this text also mentioned the use of the first known multistage rocket; this was the 'fire-dragon issuing from the water' (huo long chu shui), used mostly by the Chinese navy. That southern China and Laotian community rocket festivals might then have been key in the spread of rocketry in the Orient was proposed by Frank H. Winter in The Proceedings of the Twentieth and Twenty-First History Symposia of the International Academy of Astronautics.
HOW ROCKET WORKS
One of the most amazing endeavors man has ever undertaken is the exploration of space. A big part of the amazement is the complexity. Space exploration is complicated because there are so many problems to solve and obstacles to overcome. You have things like:
· The vacuum of space
· Heat management problems
· The difficulty of re-entry
· Orbital mechanics
· Micrometeorites and space debris
· Cosmic and solar radiation
· The logistics of having restroom facilities in a weightless environment
But the biggest problem of all is harnessing enough energy simply to get a spaceship off the ground. That is where rocket engines come in.
Rocket engines are, on the one hand, so simple that you can build and fly your own model rockets very inexpensively. On the other hand, rocket engines (and their fuel systems) are so complicated that only three countries have actually ever put people in orbit. In this article, we will look at rocket engines to understand how they work, as well as to understand some of the complexity surrounding them.
When most people think about motors or engines, they think about rotation. For example, a reciprocating gasoline energy in a car produces rotational energy to drive the wheels. An electric motor produces rotational energy to drive a fan or spin a disk. A steam engine is used to do the same thing, as is a steam turbine and most gas turbines.
Rocket engines are fundamentally different. Rocket engines are reaction engines. The basic principle driving a rocket engine is the famous Newtonian principle that "to every action there is an equal and opposite reaction." A rocket engine is throwing mass in one direction and benefiting from the reaction that occurs in the other direction as a result.
This concept of "throwing mass and benefiting from the reaction" can be hard to grasp at first, because that does not seem to be what is happening. Rocket engines seem to be about flames and noise and pressure, not "throwing things." Let's look at a few examples to get a better picture of reality:
· If you have ever shot a shotgun, especially a big 12-gauge shotgun, then you know that it has a lot of "kick." That is, when you shoot the gun it "kicks" your shoulder back with a great deal of force. That kick is a reaction. A shotgun is shooting about an ounce of metal in one direction at about 700 miles per hour, and your shoulder gets hit with the reaction. If you were wearing roller skates or standing on a skateboard when you shot the gun, then the gun would be acting like a rocket engine and you would react by rolling in the opposite direction.
· If you have ever seen a big fire hose spraying water, you may have noticed that it takes a lot of strength to hold the hose (sometimes you will see two or three firefighters holding the hose). The hose is acting like a rocket engine. The hose is throwing water in one direction, and the firefighters are using their strength and weight to counteract the reaction. If they were to let go of the hose, it would thrash around with tremendous force. If the firefighters were all standing on skateboards, the hose would propel them backward at great speed! When you blow up a balloon and let it go so that it flies all over the room before running out of air, you have created a rocket engine. In this case, what is being thrown is the air molecules inside the balloon. Many people believe that air molecules don't weigh anything, but they do. When you throw them out the nozzle of a balloon, the rest of the balloon reacts in the opposite direction
· The vacuum of space
· Heat management problems
· The difficulty of re-entry
· Orbital mechanics
· Micrometeorites and space debris
· Cosmic and solar radiation
· The logistics of having restroom facilities in a weightless environment
But the biggest problem of all is harnessing enough energy simply to get a spaceship off the ground. That is where rocket engines come in.
Rocket engines are, on the one hand, so simple that you can build and fly your own model rockets very inexpensively. On the other hand, rocket engines (and their fuel systems) are so complicated that only three countries have actually ever put people in orbit. In this article, we will look at rocket engines to understand how they work, as well as to understand some of the complexity surrounding them.
When most people think about motors or engines, they think about rotation. For example, a reciprocating gasoline energy in a car produces rotational energy to drive the wheels. An electric motor produces rotational energy to drive a fan or spin a disk. A steam engine is used to do the same thing, as is a steam turbine and most gas turbines.
Rocket engines are fundamentally different. Rocket engines are reaction engines. The basic principle driving a rocket engine is the famous Newtonian principle that "to every action there is an equal and opposite reaction." A rocket engine is throwing mass in one direction and benefiting from the reaction that occurs in the other direction as a result.
This concept of "throwing mass and benefiting from the reaction" can be hard to grasp at first, because that does not seem to be what is happening. Rocket engines seem to be about flames and noise and pressure, not "throwing things." Let's look at a few examples to get a better picture of reality:
· If you have ever shot a shotgun, especially a big 12-gauge shotgun, then you know that it has a lot of "kick." That is, when you shoot the gun it "kicks" your shoulder back with a great deal of force. That kick is a reaction. A shotgun is shooting about an ounce of metal in one direction at about 700 miles per hour, and your shoulder gets hit with the reaction. If you were wearing roller skates or standing on a skateboard when you shot the gun, then the gun would be acting like a rocket engine and you would react by rolling in the opposite direction.
· If you have ever seen a big fire hose spraying water, you may have noticed that it takes a lot of strength to hold the hose (sometimes you will see two or three firefighters holding the hose). The hose is acting like a rocket engine. The hose is throwing water in one direction, and the firefighters are using their strength and weight to counteract the reaction. If they were to let go of the hose, it would thrash around with tremendous force. If the firefighters were all standing on skateboards, the hose would propel them backward at great speed! When you blow up a balloon and let it go so that it flies all over the room before running out of air, you have created a rocket engine. In this case, what is being thrown is the air molecules inside the balloon. Many people believe that air molecules don't weigh anything, but they do. When you throw them out the nozzle of a balloon, the rest of the balloon reacts in the opposite direction
FORCES ACTING ON A ROCKET
The general study of the forces on a rocket or other spacecraft is called astrodynamics.
Rockets are primarily affected by the following during flight.
Thrust from the engine(s)
Gravity from celestial bodies
Drag if moving in the atmosphere
Lift; usually relatively small effect except for rocket-powered aircraft.
In addition, the inertia/centrifugal pseudo-force can be significant due to the path of the rocket around the center of a celestial body.
During a rocket launch, there is a point of maximum aerodynamic drag called Max Q. This determines the minimum aerodynamic strength of the vehicle.
These forces, with a stabilising tail present will cause the vehicle to follow a gravity turn trajectory, and this trajectory is often used during a launch
Rockets are primarily affected by the following during flight.
Thrust from the engine(s)
Gravity from celestial bodies
Drag if moving in the atmosphere
Lift; usually relatively small effect except for rocket-powered aircraft.
In addition, the inertia/centrifugal pseudo-force can be significant due to the path of the rocket around the center of a celestial body.
During a rocket launch, there is a point of maximum aerodynamic drag called Max Q. This determines the minimum aerodynamic strength of the vehicle.
These forces, with a stabilising tail present will cause the vehicle to follow a gravity turn trajectory, and this trajectory is often used during a launch
TYPES OF ROCKET PROPULSION
There are three basic types of rocket propulsion: chemical, nuclear, and electrical. Chemical rockets use chemicals, in solid or liquid form, for fuel and oxidizer, or the chemical that contains the oxygen needed to burn the fuel (together, the fuel and oxidizer are called the propellant). Nuclear rockets use the heat of nuclear reactions to heat chemical propellants for combustion. Electrical rockets use electric and magnetic fields (regions of space affected by electrical and magnetic energy) to accelerate and expel ions and elementary particles. Ions are atoms with positive or negative electrical charges, and elementary particles such as protons, neutrons, and electrons are the tiny building blocks of matter that make up atoms.
USES
People use all kinds of rockets for the same basic purpose: to carry objects through air and space. Missiles carry explosive devices to targets, while sounding rockets carry scientific instruments into the upper atmosphere. Launch vehicles boost satellites and other spacecraft into space, and smaller thruster rockets steer or stabilize spacecraft in space.
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