Everything about Rocketry totally explained
A
rocket or
rocket vehicle is a
missile,
aircraft or other
vehicle which obtains
thrust by the
reaction of the rocket to the ejection of fast moving
fluid from a
rocket engine. Chemical rockets work by the action of hot gas produced by the combustion of the
propellant against the inside of
combustion chambers and
expansion nozzles. This generates forces that accelerate the gas to
extremely high speed and exerts a large thrust on the rocket (since
every action has an equal and opposite reaction).
The history of rockets goes back to at least the 13th century. By the 20th century, they've enabled human
spaceflight to the Moon. In the 21st century, they've made commercial
space tourism possible.
Rockets are used for
fireworks and weaponry, as
launch vehicles for
artificial satellites,
human spaceflight and
exploration of other planets. While inefficient for low speed use, they are, compared to other propulsion systems, very lightweight and powerful, capable of attaining
extremely high speeds with reasonable efficiency.
Chemical rockets store a large amount of energy in an easily-released form, and can be very dangerous. However, careful design, testing, construction, and use minimises the risks.
History of rockets
In antiquity
According to the writings of the Roman
Aulus Gellius, in c.
400 BC, a
Greek Pythagorean named
Archytas propelled a wooden bird using steam. However, the only knowledge that exists of it's in Aulus's writings, which dates from 5 centuries later. No diagrams survive, and whether it was truly propelled by rocket power is unknown.
The availability of black powder (
gunpowder) to propel projectiles was a precursor to the development of the first solid rocket.
Ninth Century Chinese Taoist alchemists discovered black powder while searching for the
Elixir of life; this accidental discovery led to experiments in the form 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. There were reports of fire arrows and 'iron pots' that could be heard for 5
leagues (15 miles) when they exploded upon impact, causing devastation for a radius of 2,000 feet, apparently due to shrapnel. The lowering of the 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, the 'fire-dragon issuing from the water' (huo long chu shui), used mostly by the Chinese navy. Frank H. Winter proposed in
The Proceedings of the Twentieth and Twenty-First History Symposia of the International Academy of Astronautics that southern China and the
Laotian community
rocket festivals might have been key in the subsequent spread of rocketry in the Orient.
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 parts of Russia, Eastern, and Central Europe. The Mongolians had acquired 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. Rocket technology also spread to
Korea, with the 15th century wheeled
hwacha that would launch
singijeon rockets. These first Korean rockets had an amazingly long range at the time, and were designed and built by Byun Eee-Joong. They were just like arrows but had small explosives attached to the back, and were fired in swarms.
Additionally, the spread of rockets into Europe was also influenced by the
Ottomans at the siege of
Constantinople in 1453, although it's 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.
The name
Rocket comes from the
Italian Rocchetta (for example
little fuse), a name of a small firecracker created by the Italian artificer Muratori in
1379.
"
Artis Magnae Artilleriae pars prima" ("Great Art of Artillery, the First Part", also known as "The Complete Art of Artillery"), first printed in
Amsterdam in
1650, was translated to
French in
1651,
German in
1676,
English and
Dutch in
1729 and
Polish in
1963. For over two centuries, this work of
Polish-Lithuanian Commonwealth nobleman Kazimierz Siemienowicz 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 (for both military and civil purposes), including
multi-stage rockets, batteries of rockets, and rockets with
delta wing stabilizers (instead of the common guiding rods).
In 1792,
iron-cased rockets were successfully used militarily by
Tipu Sultan, Ruler of the
Kingdom of Mysore in
India against the larger
British East India Company forces 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.
Accuracy of early rockets
Early rockets were very inaccurate. Without the use of spinning or any
gimballing of the thrust, they'd a strong tendency to veer sharply off course. The early British
Congreve rockets
The accuracy problem was mostly solved in 1844 when
William Hale modified the rocket design so that thrust was slightly
vectored, causing 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.
Early manned rocketry
According to legend, a manned
rocket sled with 47 gunpowder-filled rockets was attempted in
China by
Wan Hu in the 16th Century. The alleged flight is said to have been interrupted by an explosion at the start, and the pilot didn't seem to have survived (he was never found). There are no known Chinese sources for this event, and the earliest known account is an unsourced reference in a book by an American,
Herbert S. Zim in
1945 The flight was accomplished as a part of celebrations performed for the birth of Ottoman Emperor Murat IV's daughter and was rewarded by the sultan. The device was composed of a large winged cage with a conical top with 7 rockets filled with 70 kg of gunpowder. The flight was estimated to have lasted about 200 seconds and the maximum height reached around 300 metres.
Theories of interplanetary rocketry
In 1903, high school mathematics teacher
Konstantin Tsiolkovsky (1857-1935) published
Исследование мировых пространств реактивными приборами (
The Exploration of Cosmic Space by Means of Reaction Devices), the first serious scientific work on space travel. The
Tsiolkovsky rocket equation—the principle that governs rocket propulsion—is named in his honor (although it had been discovered previously). His work was essentially unknown outside the Soviet Union, where it inspired further research, experimentation and the formation of the Cosmonautics Society.
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 worldwide attention and was both praised and ridiculed, particularly because of its suggestion that a rocket theoretically could reach the Moon. A New York Times editorial famously expressed disbelief that it was possible at all as it stated that:
"after the rocket quits our air and really starts on its longer journey it'll neither be accelerated nor maintained by the explosion of the charges it then might have left" and suggested that Professor Goddard actually:
"does not know of the relation of action to reaction, and the need to have something better than a vacuum against which to react" and talked of
"such things as intentional mistakes or oversights."
Goddard, the Times declared, apparently suggesting bad faith,
"only seems to lack the knowledge ladled out daily in high schools."
After these and other scathing criticisms, Goddard began working in isolation, and avoided publicity.
Nevertheless, in Russia, Tsiolkovsky's work was republished in the 1920s in response to Russian interest raised by 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.
In 1923,
Hermann Oberth (1894-1989) published
Die Rakete zu den Planetenräumen ("The Rocket into Planetary Space"), a version of his doctoral thesis, after the University of Munich rejected it.
Modern rocketry
Pre-World War II
Modern rockets were born when Goddard attached a supersonic (
de Laval) nozzle to a liquid fuelled 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 raising the engine efficiency from 2% to 64%. Early rockets had been grossly inefficient because of the thermal energy that was wasted in the exhaust gases. 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.
1927 the German car manufacturer
Opel began to reasearch with rockets together with Mark Valier and the rocket builder Friedrich Wilhelm Sander. In 1928, Fritz von Opel drove with a rocket car, the Opel RAK1 on the Opel raceway in Rüsselsheim, Germany. In 1929 von Opel started at the Frankfurt-Rebstock airport with the Opel-Sander RAK 1-airplane. This was maybe the first flight with a manned rocket-aircraft.
In 1927 and also in Germany, a team of amateur rocket engineers had formed the
Verein für Raumschiffahrt (German Rocket Society, or VfR), and in 1931 launched a liquid propellant rocket (using
oxygen and
gasoline).
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 propellant 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 work was also done by the Austrian professor
Eugen Sänger who worked on rocket powered spaceplanes such as
Silbervogel (sometimes called the 'antipodal' bomber.)
On November 12, 1932 at a farm in Stockton NJ, the American Interplanetary Society's attempt to static fire their first rocket (based on German Rocket Society designs) fails in a fire.
In 1932, the
Reichswehr (which in 1935 became the
Wehrmacht) 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 (followed by two former VfR members) 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 (initially called A4).
World War II
In 1943, production of the
V-2 rocket began. The V-2 had an operational range of 300 km (185 miles) and carried a 1000 kg (2204 lb) warhead, with an
amatol explosive charge. Highest point of altitude of its flight trajectory is 90 km. 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 couldn't be intercepted, their guidance system design and single conventional warhead meant that the V-2 was insufficiently accurate against military targets. The later versions however, were more accurate, sometimes within metres, and could be devastating. 2,754 people in England were killed, and 6,523 were wounded before the launch campaign was terminated. While the V-2 didn't significantly affect the course of the war, it provided a lethal demonstration of the potential for guided rockets as weapons.
Under
Projekt Amerika Nazi Germany also tried to develop and use the first
submarine-launched ballistic missile (SLBMs) and the first
intercontinental ballistic missiles (ICBMs)
A9/A10 Amerika-Raketen to bomb New York and other American cities. The tests of SLBM-variants of the A4 rocket was achieved with
U-boat submarines towing launch platforms. The second stage of the A9/A10 rocket was tested a few times in January, February and March 1945.
In parallel with the guided missile programme in Nazi Germany, rockets were also being used for aircraft, either for rapid horizontal take-off (
JATO) or for powering the aircraft (
Me 163,etc) and for vertical take-off (
Bachem Ba 349 "Natter").
Post World War II
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 the most. The US captured a large number of German rocket scientists (many of whom were members of the
Nazi Party, including von Braun) and brought them to the United States as part of
Operation Paperclip. In America, 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; notably for the
Bell X-1 to break the sound barrier. 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 the chief designer
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 Mihailovich 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 important militarily in the form of modern
intercontinental ballistic missiles (ICBMs) 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.
Fueled partly by the
Cold War, the 1960s became the decade of rapid development of rocket technology particularly in the Soviet Union (
Vostok,
Soyuz,
Proton) and in the United States (for example the
X-15 and
X-20 Dyna-Soar aircraft,
Gemini). There was also significant research in other countries, such as Britain, Japan, Australia, etc. This culminated at the end of the 60s with the manned
landing on the moon via the
Saturn V, causing the New York Times to retract their earlier editorial implying that spaceflight couldn't work:
"Further investigation and experimentation have confirmed the findings of Isaac Newton in the 17th century and it's now definitely established that a rocket can function in a vacuum as well as in an atmosphere. The Times regrets the error."
Current day
Rockets remain a popular military weapon. The use of large battlefield rockets of the V-2 type has given way to guided
missiles. However 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, ending with the
AIR-2 'Genie'
nuclear rocket, but by the early
1960s these had largely been abandoned in favor of
air-to-air missiles.
Economically, rocketry is the enabler of all
space technologies particularly satellites, many of which impact people's everyday lives in almost countless ways,
satellite navigation,
communications satellites and even things as simple as
weather satellites.
Scientifically, rocketry has opened a window on our universe, allowing the launch of
space probes to explore our
solar system,
satellites to view the Earth itself, and space-based
telescopes to obtain a clearer view of the rest of the
universe.
However, in the minds of much of the public, the most important use of rockets is perhaps
manned spaceflight. Vehicles such as the
Space Shuttle for scientific research, the
Soyuz for orbital tourism and
SpaceShipOne for suborbital tourism may show a way towards greater commercialisation of rocketry, away from government funding, and towards more widespread
access to space.
Types
There are many different types of rockets, and a comprehensive list of the basic engine types can be found in
rocket engine — the vehicles themselves 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, and in many different vehicle types such as
rocket cars and
rocket planes.
Most current rockets are chemically powered rockets (usually
internal combustion engines, but some employ a decomposing
monopropellant) that emit a hot
exhaust gas. A chemical
rocket engine can use gas propellant,
solid propellant,
liquid propellant, or a
hybrid mixture of both solid and liquid. With combustive propellants 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 (or nozzles) at the rearward-facing end of the rocket. The
acceleration of these gases through the engine exerts force ("thrust") on the combustion chamber and nozzle, propelling the vehicle (in accordance with Newton's Third Law). See
rocket engine for details.
Rockets in which the heat is supplied from a source other than a propellant, such as
solar thermal rockets, can be 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 such engines gives very high exhaust velocities (around 6-10 km/s).
Steam rockets, are another example of non chemical rockets. These rockets release very hot water through a nozzle where, due to the lower pressure there, it instantly flashes to high velocity steam, propelling the rocket. The efficiency of
steam as a rocket propellant is relatively low, but it's 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, as an alternative, with higher performance, to
cold gas thrusters for attitude jets. There are even 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, at system costs that are claimed to be greatly lower than hydrogen-based systems.
cdot g_0
is the delta-v in m/s (or ft/s)
Delta-v can also be calculated for a particular manoeuvre; for example the delta-v to launch from the surface of the Earth to
Low earth orbit is about 9.7 km/s, which leaves the vehicle with a sideways speed of about 7.8 km/s at an altitude of around 200 km. In this manoeuvre about 1.9 km/s is lost in air drag, gravity drag and gaining altitude.
Mass ratios
Mass ratio is the ratio between the initial fuelled mass and the mass after the 'burn'. Everything else being equal, a high mass ratio is desirable for good performance, since it indicates that the rocket is lightweight and hence performs better, for essentially the same reasons that low weight is desirable in sports cars.
Rockets as a group have the highest
thrust-to-weight ratio of any type of engine; and this helps vehicles achieve high
mass ratios, which improves the performance of flights. The higher this ratio, the less engine mass is needed to be carried and permits the carrying of even more propellant, this enormously improves performance.
Achievable mass ratios are highly dependent on many factors such as propellant type, the design of engine the vehicle uses, structural safety margins and construction techniques.
Staging
Often, the required velocity (delta-v) for a mission is unattainable by any single rocket because the
propellant, tankage, structure,
guidance, valves and engines and so on, take a particular minimum percentage of take-off mass.
The mass ratios that can be achieved with a single set of fixed rocket engines and tankage varies depends on acceleration required, construction materials, tank layout, engine type and propellants used, but for example the first stage of the Saturn V, carrying the weight of the upper stages, was able to achieve a mass ratio of about 10.
This problem is frequently solved by
staging — the rocket sheds excess weight (usually empty tankage and associated engines) during launch to reduce its weight and effectively increase its
mass ratio. Staging is either
serial where the rockets light after the previous stage has fallen away, or
parallel, where rockets are burning together and then detach when they burn out.
Typically, the acceleration of a rocket increases with time (if the thrust stays the same) as the weight of the rocket decreases as propellant is burned. Discontinuities in acceleration will occur when stages burn out, often starting at a lower acceleration with each new stage firing.
Energy efficiency
Rocket launch vehicles take-off with a great deal of flames, noise and drama, and it might seem obvious that they're grievously inefficient. However while they're far from perfect, their energy efficiency isn't as bad as might be supposed.
The energy density of rocket propellant is around 1/3 that of conventional hydrocarbon fuels; the bulk of the mass is in the form of (often relatively inexpensive) oxidiser. Nevertheless, at take-off the rocket has a great deal of energy in the form of fuel and oxidiser stored within the vehicle, and it's of course desirable that as much of the energy stored in the propellant ends up as
kinetic or
potential energy of the body of the rocket as possible.
Energy from the fuel is lost in air drag and
gravity drag and is used to gain altitude. However, much of the lost energy ends up in the exhaust.
And the overall energy efficiency
is:
»
Since the energy ultimately comes from fuel, these joint considerations mean that rockets are mainly useful when a very high speed is required, such as
ICBMs or
orbital launch, and they're rarely if ever used for general aviation. For example, from the equation, with an
of 0.7, a rocket flying at Mach 0.85 (which most aircraft cruise at) with an exhaust velocity of Mach 10, would have a predicted overall energy efficiency of 5.9%, whereas a conventional, modern, air breathing jet engine achieves closer to 30% or more efficiency. Thus a rocket would need about 5x more energy; and allowing for the ~3x lower specific energy of rocket propellant than conventional air fuel, roughly 15x more mass of propellant would need to be carried for the same journey.
Thus jet engines which have a better match between speed and jet exhaust speed such as
turbofans (in spite of their worse
) dominate for subsonic and supersonic atmospheric use while rockets work best at hypersonic speeds. On the other hand rockets do also see many short-range
relatively low speed military applications where their low-speed inefficiency is outweighed by their extremely high thrust and hence high accelerations.
Safety, reliability and accidents
Rockets are not inherently highly dangerous. In military usage quite adequate reliability is obtained.
Because of the enormous chemical energy in all useful
rocket propellants (greater energy per weight than explosives, but lower than
gasoline), 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 isn't perfect.
Further Information
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