Rocket Engines Essay Example For Students

Rocket Engines Essay One of the most amazing endeavors man has ever undertaken is the exploration ofspace. A big part of the amazement is the complexity. Space exploration iscomplicated because there are so many interesting problems to solve andobstacles to overcome. You have things like: The vacuum of space Heat managementproblems The difficulty of re-entry Orbital mechanics Micrometeorites and spacedebris Cosmic and solar radiation Restroom facilities in a weightlessenvironment And so on But the biggest problem of all is harnessing enoughenergy simply to get a spaceship off the ground. That is where rocket enginescome in. Rocket engines are on the one hand so simple that you can build and flyyour own model rockets very inexpensively (see the links at the bottom of thepage for details). On the other hand, rocket engines (and their fuel systems)are so complicated that only two countries have actually ever put people inorbit. In this edition of How Stuff Works we will look at rocket engines tounderstand h ow they work, as well as to understand some of the complexity. TheBasics When most people think about motors or engines, they think aboutrotation. For example, a reciprocating gasoline engine in a car producesrotational energy to drive the wheels. An electric motor produces rotationalenergy to drive a fan or spin a disk. A steam engine is used to do the samething, as is a steam turbine and most gas turbines. Rocket engines arefundamentally different. Rocket engines are reaction engines. The basicprinciple driving a rocket engine is the famous Newtonian principle thatto every action there is an equal and opposite reaction. A rocketengine is throwing mass in one direction and benefiting from the reaction thatoccurs in the other direction as a result. This concept of throwing massand benefiting from the reaction can be hard to grasp at first, becausethat does not seem to be what is happening. Rocket engines seem to be aboutflames and noise and pressure, not throwing things. So lets loo k ata few examples to get a better picture of reality: If you have ever shot ashotgun, especially a big 12 guage shot gun, then you know that it has a lot ofkick. That is, when you shoot the gun it kicks yourshoulder back with a great deal of force. That kick is a reaction. A shotgun isshooting about an ounce of metal in one direction at about 700 miles per hour. Therefore your shoulder gets hit with the reaction. If you were wearing rollerskates or standing on a skate board when you shot the gun, then the gun would beacting like a rocket engine and you would react by rolling in the oppositedirection. If you have ever seen a big fire hose spraying water, you may havenoticed that it takes a lot of strength to hold the hose (sometimes you will seetwo or three firemen holding the hose). The hose is acting like a rocket engine. The hose is throwing water in one direction, and the firemen are using theirstrength and weight to counteract the reaction. If they were to let go of thehose, it would thrash around with tremendous force. If the firemen were allstanding on skateboards, the hose would propel them backwards at great speed!When you blow up a balloon and let it go so it flies all over the room beforerunning out of air, you have created a rocket engine. In this case, what isbeing thrown is the air molecules inside the balloon. Many people believe thatair molecules dont weigh anything, but they do (see the page on helium to get abetter picture of the weight of air). When you throw them out the nozzle of aballoon the rest of the balloon reacts in the opposite direction. Imagine thefollowing situation. Lets say that you are wearing a space suit and you arefloating in space beside the space shuttle. You happen to have in your hand abaseball. If you throw the baseball, your body will react by moving away in th eopposite direction. The thing that controls the speed at which your body movesaway is the weight of the baseball that you throw and the amount of accelerationthat you apply to it. Mass multiplied by acceleration is force (f = m * a). Whatever force you apply to the baseball will be equalized by an identicalreaction force applied to your body (m * a = m * a). So lets say that thebaseball weighs 1 pound and your body plus the space suit weighs 100 pounds. Youthrow the baseball away at a speed of 32 feet per second (21 MPH). That is tosay, you accelerate the baseball with your arm so that it obtains a velocity of21 MPH. What you had to do is accelerate the one pound baseball to 21 MPH. Yourbody reacts, but it weights 100 times more than the baseball. Therefore it movesaway at 1/100th the velocity, or 0.32 feet per second (0.21 MPH). If you want togenerate more thrust from your baseball, you have two options. You can eitherthrow a heavier baseball (increase the mass), or you can throw the baseballfaster (increasing the acceleration on it), or you can throw a number ofbaseballs one after another (which is just another way of increasing the mass). Oedipus's Crime EssayIn the case of the SRBs, it gives the engine high initial thrust and lowerthrust in the middle of the flight. Solid-fuel rocket engines have threeimportant advantages: Simplicity Low cost Safety They also have twodisadvantages: Thrust cannot be controlled Once ignited, the engine cannot bestopped or restarted The disadvantages mean that solid-fuel rockets are usefulfor short-lifetime tasks (like missiles), or for booster systems. When you needto be able to control the engine, you must use a liquid propellant system. Liquid Propellant Rockets In 1926, Robert Goddard tested the first liquidpropellant rocket engine. His engine used gasoline and liquid oxygen. He alsoworked on and solved a number of fundamental problems in rocket engine design,including pumping mechanisms, cooling strategies and steering arrangements. These problems are what make liquid propellant rockets so complicated. The basicidea is simple. In most liquid propellant rocket engines, a fuel and an oxidizer(for example, gasoline and liquid oxygen) are pumped into a combustion chamber. There they burn to create a high-pressure and high-velocity stream of hot gases. These gases flow through a nozzle which accelerates them further (5,000 to10,000 MPH exit velocities being typical), and then leave the engine. Thefollowing highly simplified diagram shows you the basic components. This diagramdoes not show the actual complexities of a typical engine (see some of the linksat the bottom of the page for good images and descriptions of real engines). Forexample, it is normal for either the fuel of the oxidizer to be a cold liquefiedgas like liquid hydrogen or liquid oxygen. One of the big problems in a liquidpropellant rocket engine is cooling the combustion chamber and nozzle, so thecryogenic liquids are first circulated around the super-heated parts to coolthem. The pumps have to generate extremely high pressures in order to overcomethe pressure that the burning fuel creates in the combustion chamber. The mainengines in the Space Shuttle actually use two pumping stages and burn fuel todrive the second stage pumps. All of this pumping and cooling makes a typicalliquid propellant engine look more like a plumbing project gone haywire thananything else look at the engines on this page to see what I mean. All kindsof fuel combinations get used in liquid propellant rocket engines. For example:Liquid hydrogen and liquid oxygen used in the Space Shuttle main enginesGasoline and liquid oxygen used in Goddards early rockets Kerosene and liquidoxygen used on the first stage of the large Saturn V boosters in the Apolloprogram Alcohol and Liquid Oxygen used in the German V2 rockets Nitrogentetroxide (NTO)/monomethyl hydrazine (MMH) used in the Cassini engines OtherPossibilities We are accustomed to seeing chemical rocket engines that burntheir fuel to generate thrust. There are many other ways to generate thrusthowever. Any system that throws mass would do. If you could figure out a way toaccelerate baseballs to extremely high speeds, you would have a viable rocketengine. The only problem with such an approach would be the baseballexha ust (high-speed baseballs at that) left streaming throughspace. This small problem causes rocket engine designers to favor gases for theexhaust product. Many rocket engines are very small. For example, attitudethrusters on satellites dont need to produce much thrust. One common enginedesign found on satellites uses no fuel at all pressurizednitrogen thrusters simply blow nitrogen gas from a tank through a nozzle. Thrusters like these kept Skylab in orbit, and are also used on the shuttlesmanned maneuvering system. New engine designs are trying to find ways toaccelerate ions or atomic particles to extremely high speeds to create thrustmore efficiently. NASAs Deep Space-1 spacecraft will be the first to use ionengines for propulsion. See this page for additional discussion of plasma andion engines. This article discusses a number of other alternatives. Science