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Solid Rocket

Solid rocket

Solid rockets are rockets with a motor that uses solid propellants (fuel/oxidizer). The Chinese or the Arabs invented solid rockets and were using them in warfare by the 13th century. All rockets used some form of solid or powdered propellant up until the 20th century. Solid rockets are considered to be safe and reliable due to the long engineering history and simple design.

Basic Concepts

20th century A simple solid rocket motor consists of a casing, nozzle, grain (propellant charge), and igniter. The grain behaves like a solid mass, burning in a predictable fashion and producing exhaust gases. The nozzle dimensions are calculated to maintain a design chamber pressure, while producing thrust from the exhaust gases. Once ignited, a solid rocket motor cannot be shut off. Modern designs may also include; steerable nozzle for guidance, avionics, recovery hardware (parachutes), self destruct mechanisms, APU's, and thermal management materials.

Design

Design begins with the total impulse required, this determines the fuel/oxidizer mass. Grain geometry and chemistry are then chosen to satisfy the required motor characteristics. The following are chosen or solved simultaneously. The results are exact dimensions for grain, nozzle and case geometries;
- The grain burns at a predictable rate, given its surface area and chamber pressure.
- The chamber pressure is determined by the nozzle orifice diameter and grain burn rate.
- Allowable chamber pressure is a function of casing design.
- The length of burn time is determined by the grain 'web thickness'. The grain may be bonded to the casing, or not. Case bonded motors are much more difficult to design, since deformation of both the case and grain, under operating conditions, must be compatible. Common modes of failure in solid rocket motors are; fracture of the grain, failure of case bonding, and air pockets in the grain. All of these produce an instantaneous increase in burn surface area, and a corresponding increase in exhaust gas and pressure, and rupture of the casing. Another failure mode is casing seal design. Seals are required in casings that have to be opened to load the grain. Once a seal fails, hot gas will erode the escape path and result in failure. This was the cause of the Space Shuttle Challenger disaster.

Grain

Solid fuel grains are usually molded from a thermoset elastomer (which doubles as fuel), additional fuel, oxidizer, and catalyst. HTPB is commonly used for this purpose. Ammonium perchlorate is the most common oxidizer used today. The fuel is cast in different forms for different purposes. Slow, long burning rockets have a cylinder shaped grain, burning from one end to the other. Most grains, however, are cast with a hollow cross section, burning from the inside out (and outside in, if not case bonded), as well as from the ends. The thrust profile over time can be controlled by grain geometry. For example, a star shaped hole down the center of the grain will have greater initial thrust because of the additional surface area. As the star points are burned up, the surface area and thrust are reduced.

Casing

The casing may be constructed from a range of materials. Cardboard is used for model engines. Steel is used for the space shuttle boosters. Filament wound graphite epoxy casings are used for high performance motors.

Nozzle

A Convergent Divergent design accelerates the exhaust gas out of the nozzle to produce thrust. Sophisticated solid rocket motors use steerable nozzles for rocket control.

Performance

Solid fuel rocket motors have a typical specific impulse of 265 lbf·s/lb (2.6 kN·s/kg). This compares to 285 lbf·s/lb (2.8 kN·s/kg) for kerosene/Lox and ~389 lbf·s/lb (3.8 kN·s/kg) for liquid hydrogen/Lox¹. For this reason solids are generally used as initial stages in a rocket, with better performing liquid engines reserved for final stages. However, the venerable Star line motors manufactured by Thiokol have a long history as the final boost stage for satellites. This is due to their simplicity, compactness and high mass fraction. The ability of solid rockets to remain in storage for long periods, and then reliably launch at a moments notice, makes them the design of choice for military applications.

Amateur rocketry

Solid fuel rockets can be bought for use in model rocketry; they are normally small cylinders of fuel with an integral nozzle and a small charge that is set off when the fuel is exhausted. This charge can be used to ignite a second stage, trigger a camera, or deploy a parachute. Designing solid rocket motors is particularly interesting to amateur rocketry enthusiasts. The design is simple, materials are inexpensive and constructions techniques are safe. Early amateur motors were gunpowder. Later, zinc/sulfur formulations were popular. Typical amateur formulations in use today are; sugar (sucrose, dextrose, and sorbitol are all common)/potassium nitrate, HTPB (a rubber like epoxy)/magnesium/ammonium nitrate, and HTPB or PBAN/aluminum/ammonium perchlorate. Most formulations also include burn rate modifiers and other additives, and also possibly additives designed to create special effects, such as colored flames, thick smoke, or sparks. Amateur rocket builders are very active in hybrid motor research.

Advanced research

- Environmentally sensitive fuel formulations
- Ramjets with solid fuel
- Variable thrust designs based on variable nozzle geometry.
- hybrid rockets that use solid fuel and throttleable liquid or gaseous oxidizer

References

External links

- [http://www.braeunig.us/space/propuls.htm Robert A. Braeunig rocket propulsion page]
- [http://www.astronautix.com/articles/comlants.htm Astronautix Composite Solid Propellants ]
- [http://www.translatorscafe.com/cafe/MegaBBS/thread-view.asp?threadid=5069&messageid=63174]
- [http://www.esa.int/SPECIALS/Launchers_Access_to_Space/ASEDYQI4HNC_0.html Ariane 5 SRB]
- [http://www.tripoli.org/ Amateur High Power Rocketry Association]
- [http://www.nakka-rocketry.net/ Nakka-Rocketry (Design Calculations and Propellent Formulations)] Category:Spacecraft propulsion Category:Rocket fuels

Fuel

:For information on the band, see Fuel (band). :For the workstation, see SGI Fuel. Fuel is material with one type of energy which can be transformed into another usable energy. A common example is potential energy being converted into kinetic energy, (as heat and mechanical work). In many cases this is just something that will burn.

Fuels

Solid fuels

burn There are many different types of fuel. Solid fuels include coal, wood and peat. All these types of fuel are combustible, they create fire and heat. Coal was burnt by steam trains to heat water into steam to move parts and provide power. Peat and wood are mainly used for domestic and industrial heating, though peat has been used for power generation, and wood-burning steam locomotives were common in times past. Steam power is becoming more and more desirable as oil and gas supplies begin to run out, this is because of the wide number of possible things that can burn to heat water.

Liquid and gas fuels

Non-solid fuels include petroleum and gas (both fuel types have myriad varieties including petrol (gasoline) and natural gas). The former is widely used in the internal combustion engine while both are used in power generation.

Nuclear fuels

In a nuclear reaction a radioactive fuel will undergo fission. This provides a useful source of energy without combustion. Also, in stars (and our sun), hydrogen (a gas) is the fuel for the nuclear fusion.

Other fuel

nuclear fusion Hydrogen also features as an upcoming fuel for automobiles with Oxygen in the Fuel Cell. This involves a reaction where the hydrogen and oxygen react to produce water (H₂O) and electrical energy, which then can supply an electrical motor in order to run a car (or a variety of other uses). In this reaction the chemical energy of the chemicals is converted into electrical energy due to redox. Carbohydrates, fats, and proteins, derived from food, are the fuels for biological systems. For instance, glucose (a simple carbohydrate) combines with oxygen to produce water, carbon-dioxide, and a release of energy. In the bodies of most animals, the released energy is used by the muscles.

Fuel values

Main article: Fuel value. The fuel value is the quantity of potential energy in a food or other substance.

Oxidizer

An oxidizing agent is a substance that oxidizes another substance in electrochemistry or redox chemical reactions in general. In doing so, the oxidizing agent, sometimes called an oxidizer, becomes reduced. Because the plum oxidizing agent receives electrons it is also known as an electron acceptor.

Common oxidizing agents

- Hypochlorite and other hypohalite compounds
- Bleach (probably the most common household oxidizer)
- Iodine and other halogens
- Chlorite, chlorate, perchlorate, and other analogous halogen compounds
- Permanganate compounds
- Cerium compounds
- Hexavalent chromium compounds such as chromic and dichromic acids and chromium trioxide and chromate/dichromate compounds
- Peroxide compounds
- Tollen's Reagent
- Swern oxidation
- Kornblum oxidation
- Ozone
- Osmium tetroxide (OsO4)
- Pyridinium chloride (PCC)

Common oxidizing agents and their products

There are many other oxidizing agents too numerous to list here.

Arabs

The Arabs ((Arabic: عرب ʻarab) are a large ethnic group widespread in the Middle East and North Africa, originating in the Arabian Peninsula of southwest Asia.

Who is an Arab?

The definition of who an Arab is has several aspects:
- Ethnic identity: someone who considers himself to be an Arab (regardless of racial or ethnic origin) and is recognized as such by others.
- Linguistic: someone whose first language is Arabic (including any of its varieties); this definition covers more than 200 million people.
- Genealogical: someone who can trace his or her ancestry back to the original inhabitants of the Arabian Peninsula.
- Political: someone who is a resident or citizen of a country where Arabic is an official or national language, or is a member of the Arab League or is part of the wider Arab world; this definition would cover more than 300 million people, but it is rather simplistic and rigid in that it excludes the entire Diaspora but includes indigenous or migrant minorities The relative importance of these factors is estimated differently by different groups. Most people who consider themselves Arabs do so on the basis of the overlap of the political and linguistic definitions. However, some members of groups which fulfill both criteria reject the identity on the basis of the genealogical definition; Lebanese Maronites, for example, may reject the Arab label in favor of a narrower Phoenecian-Lebanese national identity. Groups which use a non-Arabic liturgical language - such as Copts in Egypt - are especially likely to be considered non-Arab. Not many people consider themselves Arab on the basis of the political definition without the linguistic one—thus, Kurds or Berbers do not usually identify themselves as Arab—but some do (for instance, some Berbers do consider themselves Arabs, and Kurds were in some historical circumstances seen as Arabs or Turks or Persians). In addition, a majority of the population of Qatar and the United Arab Emirates is made up of non-citizen non-Arab immigrants and so the political definition does not apply there either. A hadith of questionable authenticity[http://www.islamtoday.com/show_detail_section.cfm?q_id=266&main_cat_id=11], related by Ibn Asakir in Târîkh Dimashq and attributed by its narrator Salmân b. `Abd Allah to Islam's prophet Muhammad, expresses a common sentiment in declaring that: :"Being an Arab is not because of your father or mother, but being an Arab is on account of your tongue. Whoever learns Arabic is an Arab." According to Habib Hassan Touma (1996, p.xviii), "An 'Arab', in the modern sense of the word, is one who is a national of an Arab state, has command of the Arabic language, and possesses a fundamental knowledge of Arabian tradition, that is, of the manners, customs, and political and social systems of the culture." On its formation in 1946, the Arab League defined an "Arab" as follows: :"An Arab is a person whose language is Arabic, who lives in an Arabic speaking country, who is in sympathy with the aspirations of the Arabic speaking peoples." As a number of the Prophet companions were of non-Arab descent, Salman the Persian, Suhaib the Roman and Bilal from Abisinia. The genealogical definition was widely used in medieval times (Ibn Khaldun, for instance, does not use the word Arab to refer to "Arabized" peoples, but only to those of originally Arabian descent), but is usually no longer considered to be particularly significant.

Religions

Before the coming of Islam, most Arabs followed a religion featuring the worship of a number of deities, including Hubal, Wadd, Al-Lat, Manat, and Uzza, while some tribes had converted to Christianity or Judaism, and a few individuals, the hanifs, had apparently rejected polytheism in favor of a vague monotheism. The most prominent Arab Christian kingdoms were the Ghassanid and Lakhmid kingdoms. With the expansion of Islam, the majority of Arabs rapidly became Muslim, and the pre-Islamic polytheistic traditions disappeared. At present, most Arabs are Muslims. Sunni Islam dominates in most areas, overwhelmingly so in North Africa; Shia Islam is prevalent in Bahrain, southern Iraq and adjacent parts of Saudi Arabia, northern Yemen, and southern Lebanon, as well as parts of Syria. The tiny Druze community, belonging to a secretive offshoot of Islam, is usually considered Arab, but sometimes considered an ethnicity in its own right. Reliable estimates of the number of Arab Christians, which in any case depends on the definition of "Arab" used, vary. According to [http://arabworld.nitle.org/texts.php?module_id=6&reading_id=63&sequence=4 Fargues 1998], "Today Christians only make up 9.2 per cent of the population of the Near East". In Lebanon they now number only about 40 per cent of the population, in Syria they make up about 10 to 15 per cent, in the Palestinian territories the figure is 3.8 per cent, and in Israel Arab Christians constitute 2.1 per cent. In Egypt, they constitute 5.9 per cent of the population, and in Iraq they presumably comprise 2.9 per cent of the populace. Most North and South American Arabs (about two-thirds) are Arab Christians, particularly from Syria, Palestine, and Lebanon. Arabic-speaking Jews - mainly Mizrahi Jews and Yemenite Jews - are today usually not categorised as Arab. Prior to the emergence of the term Mizrahi, the term "Arab Jews" (Yehudim ‘Áravim, יהודים ערבים) was used to describe Jews of Arab world. The term is rarely used today. The few remaining Jews in the Arab countries reside mostly in Morocco. Between the late 1940s and early 1960s, following the creation of the state of Israel, most Arabic-speaking Jews left their countries of birth. Most are now concentrated in Israel, but many also live in France (see Jewish exodus from Arab lands).

History

The first written attestation of the ethnonym "Arab" occurs in an Assyrian inscription of 853 BC, where Shalmaneser III lists a King Gindibu of mâtu arbâi (Arab land) as among the people he defeated at the Battle of Karkar. Some of the names given in these texts are Aramaic, while others are the first attestations of Proto-Arabic dialects. The Hebrew Bible likewise refers occasionally to peoples called `Arvi (or variants thereof), translated as "Arab" or "Arabian". The scope of the Hebrew term at this early stage is unclear, but it seems to have referred to various desert-dwelling tribes in the Syrian Desert and Arabia. Its earliest attested use referring to the southern "Qahtanite" Arabs is much later. Proto-Arabic, or Ancient North Arabian, texts give a clearer picture of the Arabs' emergence into history. The earliest such texts are written not in the modern Arabic alphabet, nor in its Nabataean ancestor, but in variants of the Epigraphic South Arabian musnad, beginning in the 8th century BC with the Hasaean inscriptions of eastern Saudi Arabia, and continuing from the 6th century BC on with the Lihyanite texts (in southeastern Saudi Arabia) and the Thamudic texts (found throughout Arabia and the Sinai, and not in reality connected with Thamud). Later come the Safaitic inscriptions (beginning in the 1st century BC) and the many Arabic personal names attested in Nabataean inscriptions (which are, however, written in Aramaic.) From about the 2nd century BC, a few inscriptions from Qaryat al-Faw (near Sulayyil) reveal a dialect which is no longer considered "Proto-Arabic", but Pre-Classical Arabic. By the fourth century AD, the Arab kingdoms of the Lakhmids in southern Iraq and Ghassanids in southern Syria had emerged just south of the Fertile Crescent and ended up allying respectively with the Sassanid and Byzantine Empires. Thus they were constantly at war with each other on behalf of their imperial patrons. However, their courts were responsible for some notable examples of pre-Islamic Arabic poetry, and for some of the few surviving pre-Islamic Arabic inscriptions in the Arabic alphabet. The Lakhmid kingdom was dissolved by the Sassanids in 602, while the Ghassanids would hold out until engulfed by the expansion of Islam. During the 8th and 9th centuries, the Arabs (specifically the Umayyads, and later Abbasids) forged an empire whose borders touched southern France in the west, China in the east, Asia Minor in the north, and the Sudan in the south. This was one of the largest land empires in history. Throughout much of this area, the Arabs spread the religion of Islam and the Arabic language (the language of the Qur'an) through conversion and assimilation. Many groups came to be known as "Arabs" not through descent but through Arabization. Thus, over time, the term Arab came to carry a broader meaning than the original ethnic term. Many Arabs in Sudan, Morocco, Algeria and elsewhere became Arab through Arabization. Arab nationalism declares that Arabs are united in a shared history, culture and language. Arab nationalists believe that Arab identity encompasses more than outward physical characteristics, race or religion. A related ideology, Pan-Arabism, calls for all Arab lands to be united as one state. Anti-Arabism is hate or prejudice against Arabs. It is usually also associated with anti-Muslim hatred.

Traditional genealogy

Medieval Arab genealogists divided the Arabs into three groups:
- the "ancient Arabs", tribes that had been destroyed or vanished, such as Ad and Thamud; they are often alluded to in the Qur'an as examples of God's power to destroy wicked peoples.
- the "Pure Arabs" of South Arabia, descending from Qahtan. The Qahtanites (Qahtanis) are said to have migrated the land of Yemen following the destruction of the Ma'rib Dam (sadd Ma'rib). The Qahtanite Arabs were responsible for the ancient civilizations of Yemen, notably including that of the Sabaeans (known in the Bible as Sheba.)
- The "Arabized Arabs" (musta`ribah) of North Arabia, descending from Adnan, supposed to be a descendant of Ishmael (Ismail), the eldest son of Abraham and Hagar. The Arabic language as it is spoken today in its classical Quranic form was the result of a mix between the original Arabic tongue of Qahtan and the northern Arabic which shares a great deal with northern Semitic languages from the Levant. The Arabs take a great pride in their language and it's survival as usable and comprehendable language for over thousand years. In Jewish and Christian traditions, the identification of the Ishmaelites, described in the Bible as a people of the Arabian wilderness, with Arabs began at least by the time of Josephus, and became standard centuries prior to Islam (in which the term "Hagarenes", a pun on the Arabic muhajir and the name of Hagar, was commonly used.) Efforts to reconcile the Biblical and Arab genealogies later led to the identification of Joktan with Qahtan, probably due to his Biblical identification as the ancestor of Hazarmaveth (Hadramawt) and Sheba.

Etymology

The term "Arab" or "Arabian" (and cognates in other languages) has been used to translate several different but similar sounding words in ancient and classical texts which do not necessarily have the same meaning or origin. The etymology of the term is of course closely linked to that of the place name "Arabia". Although the term mâtu arbâi describing Gindibu in Assyrians texts is conventionally translated of Arab land, nothing is known with certainty about the exact location or extent of the land being referred to, nor what literal meaning the name had. In fact several different ethnonyms are found in Assyrian texts that are conventionally translated "Arab": Arabi, Arubu, Aribi and Urbi. The presence of Proto-Arabic names amongst those qualified by the terms arguably justifies the translation "Arab" although it is not certain if they all in fact represent the same group. In Hebrew the words `arav and `aravah literally mean "desert" or "steppe". In the Hebrew Bible the latter feminine form is used exclusively for the Arabah, a region associated with the Nabateans, who spoke Arabic. The former masculine form is used in Isaiah 21:13 and Ezekiel 27:21 for the region of the settlement of Kedar in the Syrian Desert. 2 Chronicles 9:14 contrasts “kings of `arav " with “governers of the country” when listing those who brought tribute to King Solomon. The word is typically translated Arabia and is the name for Arabia in Modern Hebrew. The New Revised Standard Version of the Bible uses instead the literal translation “desert plain” for the verse in Isaiah. The adjectival noun `aravi formed from `arav is used in Isaiah 13:20 and Jeremiah 3:2 for a desert dweller. It is typically translated Arabian or Arab and is the modern Hebrew word for Arab. The New Revised Standard Version uses the translation "nomad" for the verse in Jeremiah. In the Bible, the word `arav is closely associated with the word `erev meaning a "mix of people" which has identical spelling in unvowelled text. Jeremiah 25:24 parallels "kings of `arav " with "kings of the `erev that dwell in the wilderness". The account in 1 Kings 10:15 matching 2 Chronicles 9:14 is traditionally vowellized to read "kings of the `erev ". The people in question are understood to be the early Nabateans who do indeed appear to have been a mix of different tribes. The medieval writer Ibn an-Nadim, in Kitab al-Fihrist, derived the word from a Syriac pun by Abraham on the same root: in his account, Abraham addresses Ishmael and tells him u`rub, from Syriac `rob, "mingle". The early Nabateans are also referred to as `arvim in Nehemiah 4:7 and the singular `arvi is applied to Geshem a leader who opposed Nehemiah. This term is identical to `aravi in unvowelled text but traditionally vowelized differently. It is usually translated "Arabian" or "Arab" and was used in early 20th century Hebrew to mean Arab. However it is unclear if the term related more to `arav or to `erev. On the one hand its vowelization resembles that of the term `arvati (Arbathite) which is understood as an adjective formed from `aravah; thus it is plausibly a variant of `aravi. On the other hand it is used in 2 Chronicles 21:16 for a seemingly different people located in Africa plausibly the same Africans referred to as an `erev (mix of people) in Ezekiel 30:5. The words `aravim (plural of `aravi) and `arvim appear the same in unvowelled texts as the word `orvim meaning ravens. The occurrences of the word in 1 Kings 17:4-6 are traditionally vowellized to read `orvim. In the Talmud (Chullin 5a) a debate is recorded as to whether the passage refers to birds or to a people so named, noting a Midianite chieftain named Oreb (`orev: raven) and the place of his death, the Rock of Oreb. Jerome understood the term as the name of a people of a town which he described as being in the confines of the Arabians. (Genesis Rabba mentions a town named Orbo near Beth Shean.) One meaning of the root `-r-b in Hebrew is "exchange/trade" (la'arov: "to exchange", ma`arav: "merchandise") whence `orvim can also be understood to mean "exchangers" or "merchants", a usage attested in the construct form in Ezekiel 27:27 which speaks of `orvei ma`aravekh: "exchangers of thy merchandise". The Ferrar Fenton Bible translates the term as "Arabians" in 1 Kings 17:4-6. In Hebrew, the word `arav has the same triconsonantal root as the root meaning "west" (ma`arav) "setting sun" or "evening" (ma`ariv, `erev). The direct Arabic cognate of this is gharb ("west", etc.) rather than `arab; however, in Ugaritic, a language which normally preserves proto-Semitic gh, this root is found with `ayin, adding confusion. The Assyrian forms may plausibly be borrowings from Aramaic or Canaanite of either root, referring to land lying to the west in the latter case; the latter possibility is perhaps strengthened by the later Greek use of the term Saracen, with the parallel meaning in Arabic of "Easterners" (sharqiyyûn.) One meaning of the word Arab in Arabic is clear; clear as in comprehensible rather than as in pure. Bedouin elders still use this term with the same meaning; those whose speech they comprehend (ie Arabic-speakers) they call Arab, and those whose speech is of unknown meaning to them, they call Ajam (ajam or ajami). This is similar to how the ancient Greeks used the term Barbarian to desribe non-Greeks - Barbarian essentially meant that when they spoke their speech sounded like "Bar Bar Bar", ie. incomprehensible. In the Persian Gulf region, the term Ajam is often used to refer to the Persians. Another explanation derives the word from an old Semitic stem `.R.B., with a metathetical alternative `.B.R., both meaning travelling around the land, that is, nomadic. From that root, the terms Arab(Arabi) and Hebrew(Ebri), meaning nomads, are derived.
References

- Habib Hassan Touma (1996). The Music of the Arabs, trans. Laurie Schwartz. Portland, Oregon: Amadeus Press. ISBN 0931340888.
- Edward Lipinski, Semitic Languages: Outlines of a Comparative Grammar, 2nd ed., Orientalia Lovanensia Analecta: Leuven 2001
- [http://www.newadvent.org/cathen/01663a.htm The Catholic Encyclopedia, Robert Appleton Company, 1907, Online Edition, K. Night 2003: article Arabia]
- http://www.cia.gov/cia/publications/factbook/geos/le.html#People
See also

- Ababda
- Arabia
- Arab League
- Arab World
- Arabic alphabet
- Arabic language
- Bedouin
- Nabataeans
- Pan-Arabism
- Semitic
External links

- [http://www.aaiusa.org/arab_world.htm Maps of the Arab World]
- [http://www.albawaba.com News from Arabic countries]
- [http://www.ameinfo.com Business news from Arab countries]
- [http://www.bayt.com Jobs and Careers in the Arab World]
- [http://nabataea.net/arabia.html Arabia in ancient history] - with a discussion of the ancient usage of the word Arab
- [http://arabworld.nitle.org An Online Resource on Arab Culture and Civilization]
- [http://www.geocities.com/martinkramerorg/ArabNationalism.htm Arab Nationalism: Mistaken Identity] by Martin Kramer
- [http://www.al-islam.org/al-tawhid/arabnationalism.htm A Criticism of the Idea of Arab Nationalism] als:Araber ko:아랍인 ja:アラブ人

20th century

The 20th century lasted from 1901 to 2000 in the Gregorian calendar. Common usage sometimes regards it as lasting from 1900 to 1999, but this is incorrect since counting of calendar years begins with the year 1. The 20th century is also sometimes known as the nineteen hundreds (1900s). Decades are almost always considered as starting with the "0" year and named accordingly ("1960s", etc.). However, a number of arguments have been used to justify the common usage. One was advanced, erroneously, by Stephen Jay Gould. He claimed that the first decade had only nine years, thus contradicting the definition of decade equaled 10 years. Another argument is that the astronomical year numbering system for years does have a year zero, the year normally known as 1 BC. In 2000 the International Organization for Standardization clarified ISO 8601 to use the astronomical year numbering system, which could be interpreted as retrospectively endorsing all the people who had celebrated the new century a few months earlier. The term is also used to describe various periods that overlap with the calendar definition, most notably the Short twentieth century, which claims that the 20th Century spanned from 1914 to 1989, rendering the pre-WWI 1900s into the 19th Century and putting the 1990s at the beginning of the 21st Century. Indeed, the part of the 20th Century before World War I is quite identical to the late 1800s culturally and technologically and the 1990s decade pointed in many ways (such as the rise of the Internet) to the 21st Century and is seen by some as not being truly a part of the 20th Century.

Overview

The twentieth century saw a remarkable shift in the way that vast numbers of people lived, as a result of technological, medical, social, ideological, and political innovations. Terms like ideology, world war, genocide, and nuclear war entered common usage and became an influence on the lives of everyday people. War reached an unprecedented scale and level of sophistication; in the Second World War (1939-1945) alone, approximately 57 million people died, mainly due to massive improvements in weaponry. The trends of mechanization of goods and services and networks of global communication, which were begun in the 19th century, continued at an ever-increasing pace in the 20th. In spite of the terror and chaos, the 20th century saw many attempts at world peace. As the 35th President of the United States John F. Kennedy said: :What kind of peace do we seek? I am talking about a genuine peace, the kind of peace that makes life on earth worth living. Not merely peace in our time, but peace in all time. Our problems are man-made, therefore they can be solved by man. For in the final analysis, our most basic common link is that we all inhabit this small planet, we all breathe the same air, we all cherish our children's future, and we are all mortal. Virtually every aspect of life in virtually every human society changed in some fundamental way or another during the twentieth century and for the first time, any individual could influence the course of history no matter their background. Arguably, the 20th century re-shaped the face of the planet in more ways than any previous century.
- Death rates
- Infant mortality
- Infectious disease
- Life expectancy
- Maternal death rates
- Battles Scientific discoveries such as relativity and quantum physics radically changed the worldview of scientists, causing them to realize that the universe was much more complex than they had previously believed, and dashing the hopes at the end of the preceding century that the last few details of knowledge were about to be filled in. For a more coherent overview of the historical events of the century, see The 20th century in review. The 20th century has sometimes been called, both within and outside the United States, the American Century, though this is a controversial term.

Important developments, events and achievements

Science and technology

- The assembly line and mass production of motor vehicles and other goods allowed manufacturers to produce more and cheaper products. This allowed the automobile to become the most important means of transportation.
- The invention of heavier-than-air flying machines and the jet engine allowed for the world to become "smaller". Space flight increased knowledge of the rest of the universe and allowed for global real-time communications via geosynchronous satellites.
- Mass media technologies such as film, radio, and television allow the communication of political messages and entertainment with unprecedented impact
- Mass availability of the telephone and later, the computer, especially through the Internet, provides people with new opportunities for near-instantaneous communication
- Applied electronics, notably in its miniaturized form as integrated circuits, made possible the above mentioned rise of mass media, telecommunications, ubiquitous computing, and all kinds of "intelligent" appliances; as well as many advances in natural sciences such as physics, by the use of exponentially growing calculation power (see supercomputer).
- The development of Nitrogen fertilizer, pesticides and herbicides resulted in significantly higher agricultural yield.
- Advances in fundamental physics through the theory of relativity and quantum mechanics led to the development of nuclear weapons (known informally as "the Bomb" and dropped on the industrial town of Hiroshima and the historic one of Nagasaki), the nuclear reactor, and the laser. Fusion power was studied extensively but remained an experimental technology at the end of the century.
- Inventions such as the washing machine and air conditioning led to an increase in both the quantity and quality of leisure time for the middle class in Western societies.
- Most influential inventions in the 20th century: antibiotics, oral contraceptives, new plastics, transistors, Internet
- More...

Wars and politics

- Democratic nations began to extend voting privileges to all adults.
- Rising nationalism and increasing national awareness were among the causes of World War I, the first of two wars to involve all the major world powers including Germany, France, Italy, Japan, the United States and the British Commonwealth. World War I led to the creation of many new countries, especially in Eastern Europe. Ironically, it was said by many to be the 'War to end all Wars'.
- The economic and political aftermath of World War I led to the rise of Fascism and Nazism in Europe, and shortly to World War II. This war also involved Asia and the Pacific, in the form of Japanese aggression against China and the United States. While the First World War mainly cost lives among soldiers, civilians suffered greatly in the Second -- from the bombing of cities on both sides, and in the unprecedented German genocide of the Jews and others, known as the Holocaust.
- During World War I, in Russia the Bolshevik putsch led to the Russian Revolution of 1917. After the Soviet Union's involvement in World War II, Communism became a major force in global politics, spreading all over the world: notably, to Eastern Europe, China, Indochina and Cuba. This led to the Cold War and proxy wars with the western world, including wars in Korea (1950-53) and Vietnam (1957 - 75).
- The "fall of Communism" in the late 1980s freed Eastern and Central Europe from Soviet supremacy. It also led to the dissolution of the Soviet Union and Yugoslavia into successor states, many rife with ethnic nationalism, and left the United States as the world's superpower.
- Through the League of Nations and, after World War II, the United Nations, international cooperation increased. Other efforts included the formation of the European Union, leading to a common currency in much of Western Europe, the euro around the turn of the millennium.
- The end of colonialism led to the independence of many African and Asian countries. During the Cold War, many of these aligned with the USA, the USSR, or China for defense.
- The creation of Israel, a Jewish state in a mostly Arab region of the world, fueled many conflicts in the region, which were also influenced by the vast oil fields in many of the Arab countries.
- The term Southeast Asia coined.

Culture and entertainment

- Movies, music and the media had a major influence on fashion and trends in all aspects of life. As many movies and music originate from the United States, American culture spread rapidly over the world.
- After gaining political rights in the United States and much of Europe in the first part of the century, and with the advent of new birth control techniques women became more independent throughout the century.
- Rock and Roll and Jazz styles of music are developed in the United States, and quickly become the dominant forms of popular music in America, and later, the world. The Beatles, a 1960s British Rock and Roll band, becomes one of the most successful acts of all time, and is credited, in their experimental later albums, with permanently changing what was thought possible in popular music.
- Modern art developed new styles such as expressionism, cubism, and surrealism.
- The automobile provided vastly increased transportation capabilities for the average member of Western societies in the early to mid-century, spreading even further later on. City design throughout most of the West became focused on transport via car. The car became a leading symbol of modern society, with styles of car suited to and symbolic of particular lifestyles.
- Sports became an important part of society, becoming an activity not only for the privileged. Watching sports, later also on television, became a popular activity.

Disease and medicine

- Although the availability and quality of medicine continued to improve, epidemic diseases continued to spread, aided by modern transportation. An influenza pandemic, the Spanish Flu, killed 25 million between 1918 and 1919, while AIDS is yet uncured and treatments remain too expensive for wide use in developing countries.
- Advances in medicine, such as the invention of antibiotics, decreased the number of people dying from diseases. Contraceptive drugs and organ transplantation were developed. The discovery of DNA molecules and the advent of molecular biology allowed for cloning and genetic engineering.

Natural resources and the environment

- The widespread use of petroleum in industry -- both as a chemical precursor to plastics and as a fuel for the automobile and airplane -- led to the vital geopolitical importance of petroleum resources. The Middle East, home to many of the world's oil deposits, became a center of geopolitical and military tension throughout the latter half of the century. (For example, oil was a factor in Japan's decision to go to war against the United States in 1941, and the oil cartel, OPEC, used an oil embargo of sorts in the wake of the Yom Kippur War in the 1970s).
- A vast increase in fossil fuel consumption leads to depletion of natural resources, while air pollution has led to the develoment of an ozone hole and, many believe, global warming and both local and global climate change. The problem is increased by world-wide deforestation, also causing a loss of biodiversity. The problem of a depletion of natural resources is decreased by advances in drilling technology which led to a net increase in the amount of fossil fuel that is readily obtainable at the end of the century, as compared with the amount considered obtainable at the beginning of the century.

Significant people

De Laval nozzle

A de Laval nozzle (or convergent-divergent nozzle, CD nozzle or con-di nozzle) is a tube that is pinched in the middle, making an hourglass-shape. It is used as a means of accelerating the flow of a gas passing through it. It is widely used in some types of steam turbine and is an essential part of the modern rocket engine. The nozzle was developed by Swedish inventor Gustaf de Laval in the 19th century. Its operation relies on the different properties of gases flowing at subsonic and supersonic speeds. The speed of a subsonic flow of gas will increase if the pipe carrying it narrows because the mass flow rate is constant (grams or pounds per second). The gas flow through a de Laval nozzle is isentropic (gas entropy is nearly constant) and adiabatic (heat loss or gain is nearly zero). At subsonic flow the gas is compressible; sound, a small pressure wave, will propagate through it. Near the nozzle "throat", where the cross sectional area is a minimum, the gas velocity locally becomes transonic (Mach number = 1.0). As the nozzle cross sectional area increases the gas continues to expand and the gas flow increases to supersonic velocities where a sound wave will not propagate through the gas (Mach number > 1.0). This expansion process accelerates the exhaust from the nozzle, improving its thrust. A de Laval nozzle using hot air at a pressure of 1,000 psi (6.9 MPa or 68 atm), temperature of 1470 K, would have a pressure of 540 psi (3.7 MPa or 37 atm), temperature of 1269 K at the throat, and 15 psi (0.1 MPa or 1 atm), temperature of 502 K at the nozzle exit. The expansion ratio, nozzle cross sectional area at exit divided by area at throat, would be 6.8. The specific impulse would be 151 s (1480 N·s/kg). This principle was used in a rocket engine by Robert Goddard. Walter Thiel's implementation of it made the V2 rocket possible. Category:Rocket engines Category:Jet engines

Impulse

:This article is about the physical quantity of impulse. For other meanings of the term "" please see Impulse (disambiguation) In classical mechanics, an impulse changes the momentum of an object, and has the same units and dimensions as momentum. The SI unit of impulse is the same as for momentum, and is kilogram metres per second (kg m /s ). An impulse is calculated as the integral of force with respect to time. :

\mathbf = \int \mathbf\, dt

where :I is the impulse, measured in kilogram metres per second :F is the force, measured in newtons :t is the time duration, measured in seconds In the presence of a constant force, impulse is often written using the formula :

\mathbf = \mathbf\Delta t

where :

\Delta t

is the time interval over which the force (F) is applied. Using the definition of force yields: :

\mathbf = \int \frac\, dt

\mathbf = \int d\mathbf

\mathbf = \Delta \mathbf

It is therefore common to define impulse as a change in momentum.

Hydroxy-terminated polybutadiene

Hydroxy-terminated polybutadiene (HTPB), a polymer of butadiene, is a stable and easily stored synthetic rubber, often used in tire manufacturing. HTPB is sold as one part of a two part thermoset elastomer, with a diisocyanate as the other component, which is mixed prior to molding. The diisocyante serves to cross-link the molecules of polybutadiene between the ends where the -OH (hydroxyl) sites are found. HTPB is used to bind the fuel and oxidizer into a solid mass for solid rocket motors. It is also used as a hybrid rocket fuel. Together with N₂O (nitrous oxide, or "laughing gas") as the oxidizer, it is used to power the SpaceShipOne hybrid rocket motor. It also powers all 3/4 stages of the Japanese M-V-5 satellite launchers. JAXA describe the fuel as "HTPB/AP/Al=12/68/20" which means, proportioned by mass, HTPB 12% (binder and fuel), Ammonium Perchlorate 68% (oxidiser), and Aluminium powder, 20% (fuel). Category:Organic polymers Category:Rocket fuels

Ammonium perchlorate

Properties
General
Name	Ammonium perchlorate
Chemical formula	NH₄ ClO₄
Appearance	White solid
Physical
Formula weight	117.5 amu
Melting point	Decomposes at 45785 K (240 °C)
Density	2.0 ×10³ kg/m³
Crystal structure	?
Solubility	?
Thermochemistry
Δ_fH⁰_solid	-295.77 kJ/mol
S⁰_solid	184.18 J/mol·K
Safety
NFPA 704	100px
DOT Classes	100px 100px
Ingestion	Gastrointestinal irritation can occur.
Inhalation	May cause respiratory tract irritation or pulmonary edema.
Skin	May cause irritation.
Eyes	Irritation, chance of more serious problems.
More info	[http://ull.chemistry.uakron.edu/erd/chemicals/7/6025.html Hazardous Chemical Database]
SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references

Ammonium perchlorate is a chemical compound with the formula N H₄Cl O₄. It is the salt of ammonia and perchloric acid. Like other perchlorates, it is a powerful oxidizer. This salt is used as an explosive in mining, due to the low temperature elevation that follows its decomposition. It is produced by reaction between ammonia and perchloric acid, or by double decomposition between an ammonium salt and sodium perchlorate. It crystallises in colorless rhombohedra with a relative density of 1.95. It is the least soluble of all ammonia salts with 20 g in 100g water at 0°C. It decomposes before fusion. It is an important oxidizer used in solid rocket propellants, such as the Space Shuttle Solid Rocket Boosters, as well as many other solid rockets including some fireworks, amateur and hobby high power rockets, and larger rockets used for space launch and military purposes. The PEPCON disaster happened at an ammonium perchlorate manufacturing plant. The resulting explosions measured 3.5 on the Richter scale. Category:Ammonium compounds Category:Perchlorates Category:Pyrotechnic chemicals Category:Rocket fuels ja:過塩素酸アンモニウム

Graphite-Epoxy Motor

The Graphite-Epoxy motor is a type of rocket engine used as a booster in the Delta II rocket, among others. Category:Rocketry

Solid rocket

Basic Concepts

Design

Grain

Casing

Nozzle

Performance

Amateur rocketry

Advanced research

References

See also

External links

Fuel

Fuels

Solid fuels

Liquid and gas fuels

Nuclear fuels

Other fuel

Fuel values

See also

Oxidizer

Common oxidizing agents

Common oxidizing agents and their products

See also

Arabs

Who is an Arab?

Religions

History

Traditional genealogy

Etymology

References

See also

External links

20th century

Overview

Important developments, events and achievements

Science and technology

Wars and politics

Culture and entertainment

Disease and medicine

Natural resources and the environment

Significant people

World leaders

Scientists

Humanities

Business

Aerospace pioneers

Military leaders

Spiritual figures

Artists

Music

De Laval nozzle

Impulse

See also

Hydroxy-terminated polybutadiene

Ammonium perchlorate

Graphite-Epoxy Motor

De Laval nozzle