Encyclopedia
The traditional definition of a
rocket is a
vehicle,
missile or
aircraft which obtains
thrust by the reaction to the ejection of fast moving fluid from within a
rocket engine. Often the term is also used to refer to a rocket engine.
Overview
In military use, rockets generally use solid propellant and are unguided. Rockets equipped with
warheads can be fired by ground-attack
aircraft at fixed targets such as buildings, or can be launched by ground forces at other ground targets. During the Vietnam era, there were also air-launched unguided rockets that carried a nuclear payload designed to attack aircraft formations in flight. In military terminology, the word
missile is often preferred over rocket when the weapon uses either solid or liquid propellant, and has a guidance system.
In all rockets, the exhaust is formed from propellant which is carried within the rocket prior to its release. Rocket thrust is due to the fast release of exhaust gases .
There are many different types of rockets, and a comprehensive list can be found in
spacecraft propulsion- they range in size from tiny
models such as water rockets or small solid rockets that can be purchased at a hobby store, to the enormous
Saturn V used for the
Apollo program.
Rockets are used to accelerate, change orbits, de-orbit for
landing, for the whole landing if there is no atmosphere , and sometimes to soften a parachute landing immediately before touchdown .
Most current rockets are chemically powered rockets that emit an exhaust gas. A chemical
rocket engine can use solid propellant , liquid propellant , or a hybrid mixture of both. A chemical reaction is initiated between the
fuel and the
oxidizer in the combustion chamber, and the resultant hot gases accelerate out of a
nozzle at the rearward facing end of the rocket. The
acceleration of these gases through the engine exerts force on the combustion chamber and nozzle, propelling the vehicle . See
rocket engine for details.
Not all rockets use chemical reactions. Steam rockets, for example, release superheated water through a nozzle where it instantly flashes to high velocity steam, propelling the rocket. The efficiency of
steam as a rocket propellant is relatively low, but it is simple and reasonably safe, and the propellant is cheap and widely available. Most steam rockets have been used for propelling land-based vehicles but a small steam rocket was tested in 2004 on board the UK-DMC
satellite. There are proposals to use steam rockets for interplanetary transport using either nuclear or solar heating as the power source to vaporize water collected from around the
solar system.
Rockets where the heat is supplied from other than the propellant, such as steam rockets, are classed as external combustion engines. Other examples of external combustion rocket engines include most designs for nuclear powered rocket engines. Use of
hydrogen as the propellant for external combustion engines gives very high velocities.
Due to their high exhaust velocity , rockets are particularly useful when very high speeds are required, such as orbital speed . The speeds that a rocket vehicle can reach can be calculated by the rocket equation; which gives the speed difference in terms of the exhaust speed and ratio of initial mass to final mass .
Rockets must be used when there is no other substance or force that a
vehicle may employ for propulsion, such as in space. In these circumstances, it is necessary to carry all the propellant to be used.
Common mass ratios for vehicles are 20/1 for dense propellants such as liquid
oxygen and kerosene, 25/1 for dense monopropellants such as hydrogen peroxide, and 10/1 for liquid oxygen and liquid hydrogen. However, mass ratio is highly dependent on many factors such as the type of engine the vehicle uses and structural safety margins.
Often, the required velocity for a mission is unattainable by any single rocket because the propellant, structure, guidance and engines weigh so much as to prevent the mass ratio from being high enough. This problem is frequently solved by staging - the rocket sheds excess weight during launch to reduce its weight and effectively increase its mass ratio.
Typically, the acceleration of a rocket increases with time as the weight of the rocket decreases as fuel is burned. Discontinuities in acceleration will occur when stages burn out, often starting at a lower acceleration with each new stage firing.
History
Origins of rocketry
According to the writings of the Roman Aulus Gellius the first rocket engine seems to have been c.400 BC when a greek pythagorean
philosopher named
Archytas of Tarentum propelled a wooden bird along wires using steam. However, this rocket does not appear to have been powerful enough for taking off under its own steam. Only this single account exists, and if it occurred was written hundreds of years after the fact.
The origin of rockets as most people think of them dates back over 1,000 years ago when people of the
Han Dynasty in
China began experimenting with
gunpowder and
fireworks. The explosive force of such
pyrotechnics were eventually adapted for use in propelling projectiles such as
cannon and
musket balls. Such projectiles do not contain their own fuel, and thus do not meet the definition of a rocket. Therefore the use of gunpowder to propel projectiles is a precursor to the development of the first
solid rockets.
The ancient Chinese invention of gunpowder by
Taoist alchemists, and their use of it in various forms of weapons resulted in the development of the rocket. They were initially developed for religious proceedings that were related to the worship and celebration of the Chinese Gods in the ancient Chinese religion. They were the precursors to modern
fireworks, and after extensive research, were adapted for use as artillery in warfare during the
10th century to
12th century which is when the earliest documented solid rockets are found. Some of the ancient Chinese rockets were stationed at the military fortification known as the
Great Wall of China, and employed by the elite soldiers stationed there.
Spread of rocket technology
Rocket technology first became known to Europeans following their use by the Mongols
Genghis Khan and
Ögedei Khan when they conquered Russia, Eastern Europe, and parts of Central Europe . The Mongolians had stolen the Chinese technology by conquest of the northern part of China and also by the subsequent employment of Chinese rocketry experts as
mercenaries for the Mongol military. Reports of the Battle of Sejo in the year 1241 describe the use of rocket-like weapons by the Mongols against the
Magyars.
Additionally, the spread of rockets into Europe was also influenced by the
Ottomans at the siege of
Constantinople in 1453, although it is very likely that the Ottomans themselves were influenced by the Mongol invasions of the previous few centuries. They appear in literature describing the capture of Baghdad in 1258 by the Mongols.over two centuries, the work of
Polish-Lithuanian Commonwealth nobleman Kazimierz Siemienowicz, "
Artis Magnae Artilleriae pars prima" , was used in
Europe as a basic artillery manual. The book provided the standard designs for creating rockets, fireballs, and other
pyrotechnic devices. It contained a large chapter on caliber, construction, production and properties of rockets , including
multi-stage rockets, batteries of rockets, and rockets with
delta wing stabilizers .
At the end of the 18th century,
iron-cased rockets were successfully used militarily in
India against the British by
Tipu Sultan of the
Kingdom of Mysore during the
Anglo-Mysore Wars. The British then took an active interest in the technology and developed it further during the 19th century. The major figure in the field at this time was
William Congreve. From there, the use of military rockets spread throughout Europe. At the
Battle of Baltimore in 1814, the rockets fired on
Fort McHenry by the
rocket vessel HMS
Erebus were the source of the
rockets' red glare described by
Francis Scott Key in
The Star-Spangled Banner. Rockets were also used in the
Battle of Waterloo.
Early rockets were very inaccurate. Without the use of spinning or any
gimballing of the thrust, they had a strong tendency to veer sharply off course. The early British Congreve rockets reduced this somewhat by attaching a long stick to the end of a rocket to make it harder for the rocket to change course. The largest of the Congreve rockets was the 32 pound Carcass, which had a 15 foot stick. Originally, sticks were mounted on the side, but this was later changed to mounting in the center of the rocket, reducing drag and enabling the rocket to be more accurately fired from a segment of pipe.
The accuracy problem was mostly solved in 1844 when William Hale modified the rocket design so that thrust was slightly vectored to cause the rocket to spin along its axis of travel like a bullet. The Hale rocket removed the need for a rocket stick, travelled further due to reduced air resistance, and was far more accurate.
In 1903, high school mathematics teacher
Konstantin Tsiolkovsky published
???????????? ??????? ??????????? ??????????? ????????? , the first serious scientific work on space travel. The Tsiolkovsky rocket equation—the principle that governs rocket propulsion—is named in his honor. His work was essentially unknown outside the Soviet Union, where it inspired further research, experimentation, and the formation of the Cosmonautics Society. His work was republished in the 1920s in response to Russian interest in the work of Robert Goddard. Among other ideas, Tsiolkovsky accurately proposed to use liquid oxygen and liquid hydrogen as a nearly optimal propellant pair and determined that building staged and clustered rockets to increase the overall mass efficiency would dramatically increase range.
Modern rocketry
Modern rockets were born when Robert Goddard attached a supersonic nozzle to a rocket engine's combustion chamber. These nozzles turn the hot gas from the combustion chamber into a cooler,
hypersonic, highly directed jet of gas; more than doubling the thrust and enormously raising the efficiency. Early rockets had been grossly inefficient because of the heat energy that was wasted in the exhaust gases.
In 1920, Robert Goddard published
A Method of Reaching Extreme Altitudes, the first serious work on using rockets in space travel after Tsiolkovsky. The work attracted world-wide attention and was both praised and ridiculed, particularly because of its suggestion that a rocket theoretically could reach the Moon.
In 1923,
Hermann Oberth published
Die Rakete zu den Planetenräumen , a version of his doctoral thesis, after the University of Munich rejected it.
In 1926, Robert Goddard launched the world's first liquid-fueled rocket in
Auburn, Massachusetts.
During the
1920s, a number of rocket research organizations appeared in America, Austria, Britain, Czechoslovakia, France, Italy, Germany, and Russia. In the mid-
1920s,
German scientists had begun experimenting with rockets which used liquid propellants capable of reaching relatively high altitudes and distances. A team of amateur rocket engineers had formed the
Verein für Raumschiffahrt in 1927, and in 1931 launched a liquid propellant rocket .
From 1931 to 1937, the most extensive scientific work on rocket engine design occurred in Leningrad, at the Gas Dynamics Laboratory. Well funded and staffed, over 100 experimental engines were built under the direction of
Valentin Glushko. The work included regenerative cooling, hypergolic ignition, and fuel injector designs that included swirling and bi-propellant mixing injectors. However, the work was curtailed by Glushko's arrest during Stalinist purges in 1938. Similar but much less extensive work was also done by the Austrian professor Eugen Sänger.
In 1932, the
Reichswehr began to take an interest in rocketry. Artillery restrictions imposed by the
Treaty of Versailles limited Germany's access to long distance weaponry. Seeing the possibility of using rockets as long-range
artillery fire, the Wehrmacht initially funded the VfR team, but seeing that their focus was strictly scientific, created its own research team, with Hermann Oberth as a senior member. At the behest of military leaders,
Wernher von Braun, at the time a young aspiring rocket scientist, joined the military and developed long-range weapons for use in World War II by
Nazi Germany, notably the A-series of rockets, which led to the infamous
V-2 rocket .
In 1943, production of the
V-2 rocket began. The V-2 represented the biggest step forward in rocketry ever. The V-2 had an operational range of 300 km and carried a 1000 kg warhead, with an amatol explosive charge. The vehicle was only different in details from most modern rockets, with turbopumps, inertial guidance and many other features. Thousands were fired at various Allied nations, mainly England, as well as Belgium and France. While they could not be intercepted, their guidance system design and single conventional warhead meant that the V-2 was insufficiently accurate against military targets. 2,754 people in England were killed, and 6,523 were wounded before the launch campaign was terminated. While the V-2 did not significantly affect the course of the war, it provided a lethal demonstration of the potential for guided rockets as weapons.
At the end of World War II, competing Russian, British, and U.S. military and scientific crews raced to capture technology and trained personnel from the German rocket program at
Peenemünde. Russia and
Britain had some success, but the United States benefited most. The US captured a large number of German rocket scientists and brought them to the United States as part of
Operation Paperclip. There the same rockets that were designed to rain down on
Britain were used instead by scientists as research vehicles for developing the new technology further. The V-2 evolved into the American
Redstone rocket, used in the early space program.
After the war, rockets were used to study high-altitude conditions, by radio telemetry of temperature and pressure of the atmosphere, detection of
cosmic rays, and further research. This continued in the U.S. under von Braun and the others, who were destined to become part of the U.S. scientific complex.
Independently, research continued in the
Soviet Union under the leadership of
Sergei Korolev. With the help of German technicians, the V-2 was duplicated and improved as the R-1, R-2 and R-5 missiles. German designs were abandoned in the late 1940s, and the foreign workers were sent home. A new series of engines built by Glushko and based on inventions of Aleksei Isaev formed the basis of the first ICBM, the R-7. The R-7 launched the first satellite, the first man into space and the first lunar and planetary probes, and is still in use today. These events attracted the attention of top politicians, along with more money for further research.
Rockets became extremely military important in the form of
intercontinental ballistic missiles when it was realised that nuclear weapons carried on a rocket vehicle were essentially not defensible against once launched, and they became the delivery platform of choice for these weapons.
Fuelled partly by the
Cold War, the 1960s became the decade of rapid development of rocket technology in the Soviet Union and in the United States , including research in other countries, such as Britain, Japan, Australia, etc. Culminating at the end of the 60s with the manned landing on the moon via the
Saturn V.
Rockets remain a popular military weapon. The use of large battlefield rockets of the V-2 type has given way to guided
missiles, but rockets are often used by
helicopters and light aircraft for ground attack, being more powerful than
machine guns, but without the recoil of a heavy
cannon. In the
1950s there was a brief vogue for
air-to-air rockets, including the
AIR-2 'Genie'
nuclear rocket, but by the early
1960s these had largely been abandoned in favor of
air-to-air missiles.
Hezbollah, a Lebanese militant
Shia Islamic group, used rockets in its war against
Israel in 2006. These weapons, supplied by
Syria and
Iran, included the Arash, the
C-802,
Fajr-3,
Fajr-5, and the
Zelzal. Hezbollah fired some 4000 of these rockets on Israel. Only one hit a military target, killing 12 soldiers. The rest killed dozens of civilians, both Arabic and Jewish, and caused vast ecological devastation.
However in the heart of many of the public, the most important use of rockets is manned spaceflight. Vehicles such as
Soyuz for orbital tourism and
Spaceship One for suborbital tourism show the way towards greater commercialisation of rocketry, away from government funding, and towards more widespread access to space.
Net thrust
Below is an approximate equation for calculating the Gross Thrust of a rocket:
where:
exhaust gas mass flow
jet velocity at nozzle exit plane
flow area at nozzle exit plane
static pressure at nozzle exit plane
ambient pressure
Since, unlike a jet engine, a conventional rocket motor lacks an air intake, there is no Ram Drag to deduct from the Gross Thrust. Consequently the Net Thrust of a rocket motor is equal the Gross Thrust.
The term represents the momentum thrust, which remains constant at a given throttle setting, whereas the term represents the pressure thrust term. At full throttle, the net thrust of a rocket motor improves slightly with increasing altitude, because the reducing atmospheric pressure increases the pressure thrust term.
It is however very usual to rearrange the above equation slightly:
Where:
the effective exhaust velocity in a vacuum of that particular engine.
Regulation
Under international law, the nationality of the owner of a launch vehicle determines which country is responsible for any damages resulting from that vehicle. Due to this, some countries require that rocket manufacturers and launchers adhere to specific regulations to indemnify and protect the safety of people and property that may be affected by a flight.
In the US any rocket launch that is not classified as amateur, and also is not "for and by the government," must be approved by the
Federal Aviation Administration's Office of Commercial Space Transportation , located in Washington, DC.
Accidents
Because of the enormous chemical energy in all useful rocket fuels , accidents can and have happened. The number of people injured or killed is usually small because of the great care typically taken, but this record is not perfect.
See
Space disastersFuture
- Nuclear thermal rockets have also been developed, but never deployed; they are particularly promising for interplanetary use because of their high efficiency.
- - Nuclear/solar steam rockets for interplanetary use, using abundant extraterrestrial ice.
- Nuclear pulse propulsion rocket concepts give very high thrust and exhaust velocities.
- Solar thermal rockets use solar radiation to heat a propellant.
Another class of rocket-like thrusters in increasingly common use are
ion drives, which use electrical rather than chemical energy to accelerate their reaction mass.
References
See also
External links
Governing agencies
Information sites
Experimental amateur Rocketry
