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A rocket or rocket vehicle is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction. Rocket engines push rockets forwards simply by throwing their exhaust backwards extremely fast.
Rocket innovation dates back to as early as 1200 AD. It was used in China for warfare against the Mongols. But rockets were mainly used in warfare and in fireworks. It wasn't until the 20th century that Â rockets were being experimented for spaceflight. One of the main pioneers in space flight is a Russian mathematician, Konstantin Tsiolkovsky. In his earliest manuscripts , Astronomical Drawings" he wrote about the solar system and ways of motion in free space and Â zero gravity.
Tsiolkovsky drew the primitive design of a true Space Craft, which moved in outer space with the help of reactive forces. He designed the space rocket model. He never actually built a rocket but this model he designed was a Â three level rocket Â with a control room, decompression chamber, oxygen tanks and water filled "bathtubs" to alleviate the G-loads of launch and re-entry. On the third level he installed the machinery with Â liquid oxygen and liquid hydrogen tanks and steering rudders through the exhaust at the bottom. He published "the Space train rockets" in 1929 which was about multi-stage rockets in which he mentions that multi stage rockets is the only way to reach escape velocity and fly into orbit.
His work had the mathematical formulas for space travel, space suits and even space showers for the astronauts. He suggested that liquid hydrogen and oxygen will be required to travel to space. But his work did not get any credence and was mostly ignored at that time until later when he was given the recognition in Soviet as the inventor of rocket. But Robert Goddard is credited with the liquid fuel rockets which he came up with in the 1920s. Jerome Hunsaker a rocket scientist wrote,"Every liquid-filled rocket that flies is a Goddard rocket". He is today credited as the Father of Space age.
Goddard considered October 19th as the Anniversary Day"of his Â greatest inspiration. He climbed up a cherry tree Â to cut off Â some dead branches. And as he stood there and looked at the sky he later wrote,
"as I looked toward the fields at the east, I imagined how wonderful it would be to make some device which had even theÂ possibilityÂ of ascending to Mars, and how it would look on a small scale, if sent up from the meadow at my feet. I have several photographs of the tree, taken since, with the little ladder I made to climb it, leaning against it".Â
He got dedicated to developing a rocket after his inspiring day on October 19th. He was ridiculed as the moon-rocket man by Â a local newspaper. He did not take too much interest in his schoolwork. But later on Charles Lindenbergh took interest in his work and coninced Daniel Gugenheim to give im a $50,000 grant. The Grant helped him to relcate to Roswell in New Mexico to conduct his experiments. It is here that he made Â a lot of progress in developing a gyroscope stabilizing device to get his rocket Â in a straight path into the air and also fitted it with a parachute recovery system which is used to this day. But his work was not taken seriously by the US military. On a parallel note Wernher von Braun from Germany was put in charge of rocket experimentation and he developed the "A series" rocket engines. His work was similar to Goddard's.
At the start of the 20th century i.e. in 1903, Konstantin Tsiolkovsky discussed about the multi staging rocket and also about the liquid fuels in his works. A multistage (or multi-stage) rocket is a rocket that uses two or more stages, each of which contains its own engines and propellant. A tandem or serial stage is mounted on top of another stage; a parallel stage is attached alongside another stage. The result is effectively two or more rockets stacked on top of or attached next to each other. Taken together these are sometimes called a launch vehicle. Two stage rockets are quite common, but rockets with as many as five separate stages have been successfully launched. By jettisoning stages when they run out of propellant, the mass of the remaining rocket is decreased. This staging allows the thrust of the remaining stages to more easily accelerate the rocket to its final speed and height.
In serial or tandem staging schemes, the first stage is at the bottom and is usually the largest, the second stage and subsequent upper stages are above it, usually decreasing in size. In parallel staging schemes solid or liquid rocket boosters are used to assist with lift-off. These are sometimes referred to as 'stage 0'. In the typical case, the first stage and booster engines fire to propel the entire rocket upwards. When the boosters run out of fuel, they are detached from the rest of the rocket (usually with some kind of small explosive charge) and fall away. The first stage then burns to completion and falls off. This leaves a smaller rocket, with the second stage on the bottom, which then fires. Known in rocketry circles as staging, this process is repeated until the final stage's motor burns to completion.
In some cases with serial staging, the upper stage ignites before the separation- the interstage ring is designed with this in mind, and the thrust is used to help positively separate the two vehicles.
The Taurus rocket is unusual in that its 'stage 1' ignites in flight; this designation is used because its upper three stages are identical to those of the Pegasus rocket, with the 'stage 0' booster replacing the Pegasus' carrier aircraft.
The main reason for multi-stage rockets and boosters is that once the fuel is ignited, the space and structure which contained it and the motors themselves are useless and only add weight to the vehicle which slows down its future acceleration. By dropping the stages which are no longer useful, the rocket lightens itself. The thrust of future stages is able to provide more acceleration than if the earlier stage were still attached, or a single, large rocket would be capable of. When a stage drops off, the rest of the rocket is still traveling near the speed that the whole assembly reached at burn-out time. This means that it needs less total fuel to reach a given velocity and/or altitude.
In more recent times the usefulness of the technique has come into question due to developments in technology. In the case of the Space Shuttle the costs of space launches appear to be mostly composed of the operational costs of the people involved, as opposed to fuel or equipment. Reducing these costs appears to be the best way to lower the overall launch costs. New technology that is mainly in the theoretical and developmental stages is being looked at to lower the costs of launch vehicles. More information can be found on single stage to orbit designs that do not have separate stages.
Robert Hutchings Goddard (October 5, 1882 - August 10, 1945) was an American professor, physicist and inventor who is credited with creating and building the world's first liquid-fueled rocket, which he successfully launched on March 16, 1926. Goddard and his team launched 34 rockets between 1926 and 1941, achieving altitudes as high as 2.6Â km (1.62 miles) and speeds as high as 885Â km/h (550Â mph).
As both theorist and engineer, Goddard's work anticipated many of the developments that made spaceflight possible. Two of Goddard's 214 patents - one for a multi-stage rocket design (1915), and another for a liquid-fuel rocket design (1915) - are regarded as important milestones toward spaceflight. His 1919 monograph, A Method of Reaching Extreme Altitudes, is considered one of the classic texts of 20th century rocket science. Goddard successfully applied three-axis control, gyroscopes and steerable thrust to rockets, all of which allow rockets to be controlled effectively in flight.
He came to be recognized as the father of modern rocketry. He was the first not only to recognize the scientific potential of missiles and space travel but also to bring about the design and construction of the rockets needed to implement those ideas.
A solid rocket or a solid-fuel rocket is a rocket with a motor that uses solid propellants (fuel/oxidizer). The earliest rockets were solid-fuel rockets powered by gunpowder; they were used by the Indians, Chinese, Mongols and Arabs, in warfare as early as the 13th century.
All rockets used some form of solid or powdered propellant up until the 20th century, when liquid rockets and hybrid rockets offered more efficient and controllable alternatives. Solid rockets are still used today in model rockets and on larger applications for their simplicity and reliability.
Since solid-fuel rockets can remain in storage for long periods, and then reliably launch on short notice, they have been frequently used in military applications such as missiles. The lower performance of solid propellants (as compared to liquids) does not favor their use as primary propulsion in modern medium-to-large launch vehicles customarily used to orbit commercial satellites and launch major space probes. Solids are, however, frequently used as strap-on boosters to increase payload capacity or as spin-stabilized add-on upper stages when higher-than-normal velocities are required. Solid rockets are used as light launch vehicles for low Earth orbit (LEO) payloads under 2 tons or escape payloads up to 1000 pounds.
Advantages of solid fuel.
Solid fueled rockets are much easier to store and handle than liquid fueled rockets, which makes them ideal for military applications. In the 1970s and 1980s the U.S. switched entirely to solid-fuelled ICBMs: the LGM-30 Minuteman and LG-118A Peacekeeper (MX). In the 1980s and 1990s, the USSR/Russia also deployed solid-fuelled ICBMs (RT-23, RT-2PM, and RT-2UTTH), but retains two liquid-fuelled ICBMs (R-36 and UR-100N). All solid-fuelled ICBMs on both sides have three initial solid stages and a precision maneuverable liquid-fuelled bus used to fine tune the trajectory of the reentry vehicle.
Relative to liquid fuel rockets, solid rockets have a number of disadvantages. Solid rockets have a lower specific impulse than liquid fueled rockets. It is also difficult to build a large mass ratio solid rocket because almost the entire rocket is the combustion chamber, and must be built to withstand the high combustion pressures. If a solid rocket is used to go all the way to orbit, the payload fraction is very small. (For example, the Orbital Sciences Pegasus rocket is an air-launched three-stage solid rocket orbital booster. Launch mass is 23,130 kg, low earth orbit payload is 443 kg, for a payload fraction of 1.9%. Compare to a Delta IV Medium, 249,500 kg, payload 8600 kg, payload fraction 3.4% without air-launch assistance.)
Solid rockets can often be shut down before they run out of fuel. Essentially, the rocket is vented or an extinguishant injected so as to terminate the combustion process. In some cases termination destroys the rocket, and then this is typically only done by a Range Safety Officer if the rocket goes awry. The third stages of the Minuteman and MX rockets have precision shutdown ports which, when opened, reduce the chamber pressure so abruptly that the interior flame is blown out. This allows a more precise trajectory which improves targeting accuracy.
Finally, casting very large single-grain rocket motors has proved to be a very tricky business. Defects in the grain can cause explosions during the burn, and these explosions can increase the burning propellant surface enough to cause a runaway pressure increase, until the case fails.
Liquid Propellant Rockets
A liquid-propellant rocket or a liquid rocket is a rocket with an engine that uses propellants in liquid form. Liquids are desirable because their reasonably high density allows the volume of the propellant tanks to be relatively low, and it is possible to use lightweight pumps to pump the propellant from the tanks into the engines, which means that the propellants can be kept under low pressure. This permits the use of low mass propellant tanks, permitting a high mass ratio for the rocket.
Liquid rockets have been built as monopropellant rockets using a single type of propellant, bipropellant rockets using two types of propellant, or more exotic tripropellant rockets using three types of propellant. Bipropellant liquid rockets generally use one liquid fuel and one liquid oxidizer, such as liquid hydrogen or a hydrocarbon fuel such as RP-1, and liquid oxygen. This example also shows that liquid-propellant rockets sometimes use cryogenic rocket engines, where fuel or oxidizer are gases liquefied at very low temperatures.
Tankage efficiency: Unlike gases, a typical liquid propellant has a density similar to water, approximately 0.7-1.4g/cmÂ³ (except liquid hydrogen which has a much lower density), while requiring only relatively modest pressure to prevent vapourisation. This combination of density and low pressure permits very lightweight tankage; approximately 1% of the contents for dense propellants and around 10% for liquid hydrogen (due to its low density and the mass of the required insulation).
For injection into the combustion chamber the propellant pressure needs to be greater than the chamber pressure at the injectors; this can be achieved with a pump. Suitable pumps usually use turbopumps due to their high power and lightweight, although reciprocating pumps have been employed in the past. Turbopumps are usually extremely lightweight and can give excellent performance; with an on-Earth weight well under 1% of the thrust. Indeed, overall rocket engine thrust to weight ratios including a turbopump have been as high as 133:1 with the Soviet NK-33 rocket engine.
Alternatively, a heavy tank can be used, and the pump foregone; but the delta-v that the stage can achieve is often much lower due to the extra mass of the tankage reducing performance; but for high altitude or vacuum use the tankage mass can be acceptable.
Liquid propellant rockets can be throttled in realtime, and have good control of mixture ratio; they can also be shut down, and, with a suitable ignition system or self-igniting propellant, restarted.
A liquid rocket engine (LRE) can be tested prior to use, whereas for a solid rocket motor a rigorous quality management must be applied during manufacturing to insure high reliability. 
A LRE can be reused for several flights, like in the Space Shuttle.
Disadvantages of liquid rockets
Bipropellant liquid rockets are simple in concept but due to high temperatures and high speed moving parts, very complex in practice.
Use of liquid propellants can be associated with a number of issues:
Because the propellant is a very large proportion of the mass of the vehicle, the center of mass shifts significantly rearward as the propellant is used; one will typically lose control of the vehicle if its center mass gets too close to the center of drag.
When operated within an atmosphere, pressurization of the typically very thin-walled propellant tanks must guarantee positive gauge pressure at all times to avoid catastrophic collapse of the tank.
Liquid propellants are subject to slosh, which has frequently led to loss of control of the vehicle. This can be controlled with slosh baffles in the tanks as well as judicious control laws in the guidance system.
Liquid propellants often need ullage motors in zero-gravity or during staging to avoid sucking gas into engines at start up. They are also subject to vortexing within the tank, particularly towards the end of the burn, which can also result in gas being sucked into the engine or pump.
Liquid propellants can leak, especially hydrogen, possibly leading to the formation of an explosive mixture.
Turbopumps to pump liquid propellants are complex to design, and can suffer serious failure modes, such as overspeeding if they run dry or shedding fragments at high speed if metal particles from the manufacturing process enter the pump.
Cryogenic propellants, such as liquid oxygen, freezes atmospheric water vapour into very hard crystals. This can damage or block seals and valves and can cause leaks and other failures. Avoiding this problem often requires lengthy chilldown procedures which attempt to remove as much of the vapour from the system as possible. Ice can also form on the outside of the tank, and later fall and damage the vehicle. External foam insulation can cause issues as shown by the Space Shuttle Columbia disaster. Non-cryogenic propellants do not cause such problems.
Non-storable liquid rockets require considerable preparation immediately before launch. This makes them less practical than solid rockets for most weapon systems.
The injector implementation in liquid rockets determines the percentage of the theoretical performance of the nozzle that can be achieved. A poor injector performance causes unburnt propellant to leave the engine, giving extremely poor efficiency.
Additionally, injectors are also usually key in reducing thermal loads on the nozzle; by increasing the proportion of fuel around the edge of the chamber, this gives much lower temperatures on the walls of the nozzle.
 Types of injectors
Injectors can be as simple as a number of small diameter holes arranged in carefully constructed patterns through which the fuel and oxidiser travel. The speed of the flow is determined by the square root of the pressure drop across the injectors, the shape of the hole and other details such as the density of the propellant.
The first injectors used on the V-2 created parallel jets of fuel and oxidizer which then combusted in the chamber. This gave quite poor efficiency.
Injectors today classically consist of a number of small holes which aim jets of fuel and oxidiser so that they collide at a point in space a short distance away from the injector plate. This helps to break the flow up into small droplets that burn more easily.
There are a variety of uses for rockets. Ever since the begining of rocketry the main use for a rocket was for use in warfare. In the mid 1900's that all changed when the U.S. and the U.S.S.R. used them to explore space. Rockets are still a very important weapon in wars and now are more deadly than ever. The two main purposes for rockets today are in warfare and in exploring space, but there are many other uses for rockets.
Rockets in the last century and also today are used for space travel, military uses, launching satellites into space and even for entertainment purposes such as fireworks.
Military Uses: Rockets are used in many military weapons such as missiles. Rockets propel the missiles towards their targets. It was not until WWII that rockets began to be used extensively in warfare. At first, they were used as air launched powered bombs to attack ground targets. Towards the end of the war, they became more powerful, and development began on air-to-air rockets for aerial combat.
Entertainment: Rockets are most commonly used for different entertainment purposes, such as fireworks.
Space Travel: NASA uses rockets to propel space ships and satellites into space. The first successful space ship launch with rockets occurred in 1969.
Sounding rockets were used to determine the makeup of the upper atmosphere. At the time, we had no real idea of what the atmosphere above 50,000 feet was like, or even how far it extended above the surface of the planet.
The sounding rockets also carried instruments that gave us brief glimpses of the Sun. This began giving us our first clues as some of the secrets of our star.
Satellites: Satellites use rockets to launch into space. The first successful satellite launch occurred in 1951.
Disadvantages of rockets
Apart from the advantages of the rockets, there are some disadvantages too.
Rockets were extensively used in the warfare and military uses. Last century has seen a lot destruction done through rockets. It has had a severe impact on humanity and the life on earth. The last century also saw the same. Whole earth became a battlefield during the two world wars in which the maximum amount of rockets and missiles were used. Maximum use of rockets was done by the countries to destroy their enemies. The bombs were attached to the rocket and then the countries were attacked. With the invention of rockets, there is always a fear of war.