Space PropulsionRESEARCH I/II
The following is a research project on Space Vehicle Propulsion. It shall consist of four sections, each discussing specific topics. Section One lays out the basic ideas of rocketry. Section Two compares Rocket Propulsion Systems, and shows the basis for the comparison. It also shows how each specific Rocket System works and Section Three gives a description of how Space Propulsion has evolved and contains a conclusion.
Section One is a brief description of the basic properties of Rocket Systems. It defines the key terms and shows how a basic rocket works. It also shows the State if The Art.
I have chosen to do my project on space vehicle propulsion. Basically, this means that my research shall be based primarily on rocketry. Rocketry is a way of propulsion that has developed in numerous ways since it was first used to propel fireworks in the 16th century. It has emerged into an extremely complicated science that few actually understand.
Most space rocketry in America is used in NASA (National Aeronautics and Space Association) space projects. NASA, a government association that focuses on space exploration, is the main user of rocket technology. It is used mostly to power their satellites and shuttles into space. Pushing an object that weighs as much as a space shuttle does directly vertical until escaping the Earth’s atmosphere requires a tremendous amount of power. This is why NASA uses rockets. Rockets are essentially the most powerful forms of propulsion there is today.
Space Vehicle Propulsion is based rocket engines. The basic principle of rocket engine is that when fuel is burned in the engine, the reaction mass is expelled at high speeds. As a result of Newton’s law of action and reaction this pushes the vehicle in the opposite direction of the one in which the reaction mass is moving. Thrust is the force that the engine exerts on all space behind it in order to ?push? the vehicle forward. Efficiency is the way that the quality of rocket engines is measured by. It is measured by the time it takes for one kilogram of propellant to create one kilogram of thrust. The goal of my research is to find out what makes these engines more efficient.
In rocketry, the state of the art is extremely hard to define, since there are so many different forms of rocketry ranging from liquid propellant rockets to fireworks. The state of the art though is probably nuclear powered rockets. It is much more efficient because it does not use chemical combustion like most rockets do. Instead NFRRs (Nuclear Fission Reactor Rockets) heat hydrogen in a fission reactor which expels the propellant at blistering speeds.
Much research is being done with NFRRs. They are still highly experimental because of the dangers that could be associated with them. The NERVA (Nuclear Engine for Rocket Vehicle Application) was one of the most extensive NFRR research projects, however it failed because of the inability figure out an approach to putting the research into a developmental stage.
Specific Rocket Propulsion Systems
Section One has laid the foundation for further research in the are of rocketry. Section two shall discuss properties of efficiency in more depth, it shall lay out the types of rockets in existence now. It shall also show which type of rocket is the most efficient. After this section, the next one shall describe how the reasons for these specific rockets efficiency and depending on the outcome of that report, the topic of the fourth shall be decided.
Efficiency is the most important part of my research as yet. Since the object of my research is to find out which type of rockets are the most efficient and why, the reader of this paper must have a basic understanding of efficiency. Once this is established, new definitions will come into play, all of these shall be crucial in the understanding of the paper.
Terms Needed To Understand Efficiency
G- a unit of acceleration [equal to 9.8 meters/second/second (accelerating at a pace of 9.8 meters per second every second)]
Specific Impulse (Isp)- A measurement in seconds of efficiency.
Properties of Efficiency
Efficiency is the most accurate indicator of rockets performance. As stated in the aforementioned definitions, specific impulse is the basic unit of measurement of rocket efficiency. Isp is found by dividing the exhaust velocity by g (definition also mentioned above). Since velocity is measured in m/s (meters per second) and each g is equal to 9.8 m/s/s (meters per second every second), the terms cancel to leave just a unit in seconds. The resulting figure, is the duration of time for which one kilogram of propellant can produce one kilogram of thrust. Thus, a higher number represents a better, and more efficient rocket. To give the reader an idea of the average Isp of several type of rockets, I have listed some average figures for efficiency of certain types of rockets below.
Average Efficiencies of Certain Rockets
Next, I have listed the Isp values for some basic types of rockets. After that I shall explain some of the most well known types of rockets.
Basic Rocket Types
An RPS (rocket propulsion system) is a powerplant that pushes a vehicle forward by ejecting matter that is stored within the vehicle. This matter is called propellant. The propellant is the most crucial part of moving a vehicle through space. Their energy source, the vehicles they are used on, and the type of propellant classify the specific types of systems.
Liquid Propellant Rockets
All LPRs (Liquid Propelled Rockets) contain the same basic devices. The next paragraph shall discuss these functions and examine their purpose.
The first such device is the thrust chamber. The thrust chamber contains an injector, a combustion chamber and a nozzle. The thrust chamber is the place where the propellants are injected, atomized, then mixed and finally burned to form reaction products in the form of gas. Next, the products are accelerated and ejected at extremely high velocities to create thrust.
The injector is a series of pipes that allow the liquid propellant to move into the combustion chamber chamber to be made into thrust while atomizing and mixing them. The exhaust nozzle is the last step in the releasing of thrust. It allows the hot gas to expand and then accelerates them to supersonic velocities. On some vehicles, the nozzle acts as a steering mechanism by placing it on an electronic axis for which it can be turned by an automated steering wheel.
There are two major types of feed systems used by LPRs; one uses pumps to move propellants to combustion chambers; the other, uses high pressure to expel propellants from their tanks.
On most space vehicles the engines are mounted in pairs at the perimeter of the craft. Normally to opposite facing thrust chambers are controlled automatedly to turn the ship. Generally, a minimum of 12 thrust chambers is required for turning.
Solid Propellant Rockets
Solid Propellant Rockets (SPRs) contains a huge number of types of engines. The propellant that is to be burned is held in the combustion chamber. The propellant charge (grain) contains chemical elements for complete burning. When it is ignited, it burns on all its exposed sides.
If the design of the grain is changed, then less can be exposed; the less exposed, the less fuel burned. The average burning rate is around 1.8 cc per second. The rate normally depends on the propellant ingredients. The more chamber pressure, the more propellant burnt.
The way to make an efficient SPR is to pack as much solid propellant into a chamber volume as possible. Theoretically, it would be ideal to burn the propellant like a cigar, from one end to the other. For this reason, scientists created an end-burning grain, which has proved extremely successful.
There are three types of electric propulsion systems (EPS); the three include electromagnetic, electrothermal and electrostatic. They are, in some ways more a rocket of the future then one of the present, somewhat like the NERVA project (see next section).
In the electrothermal system the propellant is heated or vaporized electric heaters. The hot gas is then expanded through a nozzle the way it is in a chemical rocket. In an electrostatic system, interacting electrostatic fields and small charged particles such as colloidal particles achieve acceleration. In an electromagnetic rocket, acceleration is achieved by placing propellant plasma (a high temperature, electrically natural gas that contains electrons, ions and neutral molecular species) in an electromagnetic field thus causing a reaction that releases thrust.
Unlike the aforementioned rockets, nuclear rockets do not generate its power through chemical combustion. The way its power is formed, is through nuclear fission. It heats a propellant like hydrogen in a fission reactor and the explosion expels the propellant at amazing speeds, which exceed twice what any other rocket can produce. Its efficiency rating is around 850, as compared to the 450 of the next best type, the cryogenic rocket. Unfortunately due to the extreme dangers of nuclear fission inside a shuttle, the main project for researching the nuclear rockets, NERVA, was scrubbed. Most likely, in the future, scientists will devise a plan to minimize the risks, whereupon research will begin again.
The third section of this report shall begin by indicating the steps in which rocketry was created, as to allow the reader of this paper to better understand the way rockets work. It shall show the works of Tsiolkovsky, Goddard, Oberth and a few others.
The report shall then end in a detailed conclusion. The conclusion will be based on the summary and discuss all that has been written. It shall end in giving opinions as to the future uses of the specific areas found in the research.
Development of Modern Rocketry
In around 1232 AD, in China, rockets were created. During the war with the Mongols, the Chinese would strap an early form of gunpowder to the shaft of an arrow. This made them fly longer and faster than any of the regular arrows that the Mongols used.
About ten years later, in Europe, another major discovery was made. An Englishman, Robert Bacon, created a more practical formula for gunpowder. He did this by mixing 41.2 parts saltpeter, 29.4 parts charcoal and 29.4 parts sulfur. He was able to distill saltpeter, which produces oxygen, to allow the rocket to burn faster.
In the 18th century, the British encounter encountered rocket warfare with India. The Indians probably learned the secret of rocket treat from Arab traders in the 17th century. The Indians, who were led by Hyder Ali, gave thousands of men the task of throwing rockets. The rockets were first thrown, then propelled itself. They attached an eight foot long bamboo stalk to six pound iron tube filled with fuse and powder. The rockets were able to fly up to 1.5 miles.
Tsiolkovsky, a Russian teacher, established that a rocket would work in the vacuum of space, in 1883. In 1903, he wrote a book explaining how space travel was possible, using liquid propelled rockets. He created drawings of possible space ships propelled by either liquid oxygen and liquid hydrogen or liquid oxygen and kerosene. The sketches also show valves to transport the liquid propellant into a combustion chamber and showed how vanes could be created in the exhaust for steering. He also illustrated the crew lying on their backs in a pressurized cabin in order to withstand the pressure of such high speeds. Tsiolkovsky also thought of rocket staging. Rocket staging is a series of rockets that fire one after the other. When one finishes and the other fires, the useless rocket is jettisoned. He thought this was the only way to put heavy objects such as satellites into space.
Although Tsiolkovsky thought up the ideas of advanced rocketry, still more had to be considered, and it had to become reality. The next pioneer, was the father of American rocketry, Robert Goddard. He first, created a bazooka type rocket. The bazooka was fairly large solid-propellant rocket. In 1919, he wrote a text called A Method of Reaching Extreme Altitudes. Two years later, he bagan to experiment with the liquid fuels that Tsiolkovsky. In 1926, Goddard finally launched the first liquid propelled rocket. It was fueled by gasoline and liquid oxygen. It rose to a height of 41 feet and traveled at 60 miles per hour. It only traveled 56 meters but it set the foundation for the future of rocketry. In May 1935, he released a rocket that featured gyro controlled exhaust vanes which pushed it to travel 1.5 miles above the ground at a totally unprecedented 700 miles per hour.
GERMAN ROCKET SCIENTISTS
In 1923 a German rocket scientist Hermann Oberth published The Rocket Into Planetary Space. He favored liquid propellants, as Goddard, because of their power. His experimentation inspired the creation of the Society for Space Travel. The society passionately experimented with ways to improve the liquid propellant rocket.
On February 21, 1931, a member of The Society for Space Travel, Johannes Winkler, launched the second liquid fuel rocket. Winkler’s rocket was propelled by liquid methane and liquid oxygen. It failed totally, going a mere ten feet forward. Three weeks later another rocket ascended to about 2000 feet. The entire Society for Space Travel began working on two rocket series, the Mirak and Repulsor. The late model Repulsors could reach an altitude of 1 mile.
When The Society for Space Travel ran out of money, they made a demonstration of the Repulsor for the German Army. A member, Werner Von Braun compiled some statistics for the army who gave it to Hitler. They realized that this did not violate the treaty which did not allow them to build airplanes. Hitler started the Army Weapons Department. Von Braun was placed in charge of rocket development. Within a few years Von Braun was experimenting with highly developed rockets and was firing them in secret at the island of Birkum. In 1934 he created two rockets, that could ascend to over 1.5 miles. After that, The Society for Space Travel fell apart due to financial problems.
In 1937, a rocket research station was constructed on the Baltic coast. Here the Germans created such rockets as the famous V-1 Buzz Bombs, and the mammoth V-2 which were really rocket-powered flying bombs.
In this research, it has been demonstrated how all rocket engines work. It illustrates how propellants are moved into a combustion chamber, and expelled at extremely high speeds. It shows the properties of efficiency, the basic measure by which all rockets are compared. It shows how efficiency is measure by specific impulse, which is calculated by the propellants exhaust velocity divided by g. It has given a basic comparison as to the efficiency of various rockets and has shown the reasons for being at their respective ranks. Also shown, is the pioneering of rocketry starting in the mid 1200s. All this has shown the basic properties of space propulsion
– the Rocket Engine Specifications page from the Artemis Project
(http://www.asi.org/ ) Data Book
-the Orbital Report News Agency’s Launch Vehicle database
– JPL’s Mission ; Spacecraft Library
– Mark Wade’s Encyclopedia Astronautica
– The Space Shuttle Reference Manual
– Solar electric propulsion on the Deep Space 1 probe
?Rockets? Sutton, George P Groliers Online Encyclopedia