HOW IS PAPER MADE?


Paper is a dried, compressed mat of plant fibers—nothing more, nothing less. It's a bit like clothing you can write on. No, really! Clothes are made by weaving together yarns such as cotton and wool spun from natural fibers. Paper is more like the fabric we call felt, made without the weaving stage by pressing together cellulose fibers extracted from plants and trees so they knit and fuse to form a strong, solid, but still very flexible mat.



Most paper pulp is made from trees (mainly fast-growing, evergreen conifers), though it can also be made from bamboo, cotton, hemp, jute, and a wide range of other plant materials. Smooth papers used for magazines or packaging often have materials such as china clay added so they print with a more colorful, glossy finish.



Here's the basic idea: you take a plant, bash it about to release the fibers, and mix it with water to get a soggy suspension of fibers called pulp (or stock). Then spread the pulp out on a wire mesh so the fibers knit and bond together, squeeze the water away, dry out your pulp, and what you've got is paper! Paper is really easy to make by hand (try it for yourself) but people use so much of it that most is now made by giant machines. Whichever method is used, there are essentially two stages: getting the pulp ready and then forming it and drying it into finished sheets or rolls.



Papermaking by hand



The raw plant material is placed in a large vessel filled with water and literally beaten to a pulp to make a thick suspension of fibers called half-stuff. This is formed into sheets of paper using a very basic frame made of two parts: a metal mesh called a mold that sits inside a wooden frame known as a deckle (a bit like a picture frame). The mold and deckle are dipped into the half stuff and gently agitated so an even coating forms on top, with most of the water (and some of the pulp) draining through. The deckle is then removed from the mold and the soggy mat of paper is placed on a sheet of felt. This process is repeated to make a number of interleaved sheets of paper and felt, which are then placed inside a screw-operated press and squeezed under immense pressure to squash out virtually all the remaining water. After that, the sheets of paper are taken out and hung up to dry.



Papermaking by machine



Although some expensive papers are still crafted by hand, most are churned out quickly, efficiently, and automatically by gigantic machines. Pulp is prepared for papermaking machines either mechanically or chemically. The mechanical method (generally used to make lower-grades of paper) is called the ground-wood process, because the pulp was originally made by using huge stones to grind up logs. Nowadays, pulp is prepared by giant machines that cut, wash, chop, beat, and blend wood, rags, or other raw materials into a soggy mass of fibers. In the chemical method, known as the Kraft process (from the German word for "strength," because it produces strong paper), plant materials are boiled up in strong alkalis such as sodium sulfide or sodium hydroxide to produce fibers. At this point, loading materials (surface coatings such as clays), dyes (to make colored paper), and sizes (to strengthen and waterproof and prevent inks from spreading) can be added to the mixture to change the properties of the finished paper (sometimes they're added later).



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HOW ARE DIFFERENT PAPERS DESCRIBED?


There is no such thing as good or bad paper, just paper that is good or bad for a particular job. Blotting .paper needs to be able to absorb ink, for example, while paper for printing must let the ink sit on the surface, so that the printing is crisp and clear. Most paper is described firstly by weight. Paper for a children’s picture book might weigh 150 grams per square metre. It is said to be 150gsm paper.



Paper comes in different types, with different sizes, weights, thickness and finishes. Getting the right types of paper for your office printing needs may be a little complicated. However, grasping the basics of paper types will help you make the right choices while stocking up on your office supplies. Office documents serve different purposes and as such, there are different types of paper suitable for each need. Read on to find out the common types of paper and a brief description of each. Many catalogues and brochures are made from paper.



Bond Paper



This paper is more durable and is commonly used in electronic printing. The basic size is 17 inches by 22 inches and weight range is between 16 and 36 pounds. The size may also vary slightly. It is commonly used to make letterheads, envelops, invoices or most documents printed using laser and inkjet printers.



Bristol Paper



Also known as Bristol board, this paper is a heavyweight, thick and uncoated paper. The basic size is 22.5 inches by 28.5 inches with a 0.006 inch thickness. Its strength makes it perfect for use in making book covers, tickets, brochures, file folders, among others.



Recycled Paper



If you are looking to reduce your environmental impact, then using recycled paper may be one step in fulfilling this goal. It is important to note that recycled paper may be slightly expensive than the standard “virgin paper.” This is because it is generally produced in low quantities and hence, per unit production cost may be high. That said, the paper can be used for printing most office documents such as memos and reports.



Index Card



Index card comes in three sizes, 3 inches by 5 inches, 4 inches by 6 inches and 5 inches by 8 inches; and three weights: 90, 110, and 140 pounds. The paper is usually thin and stiff, and is perfect for making magazine inserts, postcards, and index cards. It is budget-friendly and holds ink well, making it ideal for most print projects that require durable paper.



Tag Paper



This type of paper is tough and durable, making it ideal for frequent handling. It is commonly used in making print hand-tags that can be found on consumer goods.



Text Paper



What are the different types of paper These are uncoated and can be used to satisfy a variety of office requirements such as printing office stationery, letterheads or envelops. They are economical, and with their multiple uses in the office, they make a good choice for normal office use.



Coated Paper



These types of paper usually come with a clay coating to create a gloss on the paper surface. The coating gives a shining effect and is better in holding ink as compare to uncoated paper. There are two major types of coated papers: gloss coated paper and matt-coated paper. Gloss coated paper is more shiny and hence, can be used in making brochures and flyers. On the other hand, matt-coated paper is not shiny as it is coated with matt instead of gloss. This eliminates the glare that comes from shiny paper, making it ideal for making reports or leaflets. In between gloss and matt, there is silk coated paper with a silky and smooth coating. It has multiple uses, including making magazines and books.



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HOW DO CANALS CLIMB HILLS?


Water, left to its own devices, always flows from its highest point to its lowest, until the two points are on the same level. If a canal sloped as it climbed a hill, its water would simply flow to the bottom. One solution is to bore a tunnel through the hill, so that the canal can continue on a level course, but sometimes this is too costly or geologically impossible. Building locks can solve this problem.



Canals are waterways channels, or artificial waterways, for water conveyance, or to service water transport vehicles. They may also help with irrigation. It can be thought of as an artificial version of a river.



In most cases, the engineered works will have a series of dams and locks that create reservoirs of low speed current flow. These reservoirs are referred to as slack water levels, often just called levels.



A canal is also known as a navigation when it parallels a river and shares part of its waters and drainage basin, and leverages its resources by building dams and locks to increase and lengthen its stretches of slack water levels while staying in its valley. In contrast, a canal cuts across drainage divide atop a ridge, generally requiring an external water source above the highest elevation.



Many canals have been built at elevations towering over valleys and other water ways crossing far below. Canals with sources of water at a higher level can deliver water to a destination such as a city where water is needed. The Roman Empire’s aqueducts were such water supply canals.



Caen Hill Locks are a flight of 29 locks on the Kennet and Avon Canal, between Rowde and Devizes in Wiltshire, England. The 29 locks have a rise of 237 feet in 2 miles (72 m in 3.2 km) or a 1 in 44 Gradient. The locks come in three groups: the lower seven locks, Foxhangers Wharf Lock to Foxhangers Bridge Lock, are spread over 3?4 mile (1.2 km); the next sixteen locks form a steep flight in a straight line up the hillside and are designated as a scheduled monument. Because of the steepness of the terrain, the pounds between these locks are very short. As a result, fifteen of them have unusually large sideways-extended pounds, to store the water needed to operate them. A final six locks take the canal into Devizes. The locks take 5–6 hours to traverse in a boat.



A lock consists of two gates across the canal, with mechanisms for opening them on the towpath.



To climb to a higher level of the canal, a boat enters the first lock gate, which is closed behind it.



Paddles in the second lock gate are opened so that water can flow in, gradually raising the level of water in the lock.



When the water ahead is level with that in the lock, the gates are opened and the boat can move on.



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WHEN WAS THE HEYDAY OF CANAL-BUILDING?


For thousands of years, people have transported heavy goods along waterways. The first canals were probably built to join existing navigable rivers. In the fifteenth century, the Aztec city of Tenochtitlan had a sophisticated series of canals, providing transport for goods and people. Venice, in Italy, although a smaller city, was also built on a system of canals rather than roads. However, the golden age of canal-building probably came with the Industrial Revolution, when there was an enormous need for cheap and easy ways to carry the goods made in factories to the nearest port. Canal boats, powered at first by a horse on the towpath and later by coal-fired steam engines, could carry enormous loads much more conveniently than horse drawn carts on bumpy roads.



The British canal system of water transport played a vital role in the United Kingdom’s Industrial Revolution at a time when roads were only just emerging from the medieval mud and long trains of packhorses were the only means of "mass" transit by road of raw materials and finished products. The UK was the first country to develop a nationwide canal network.



The canal system dates to Roman Britain, but was largely used for irrigation or to Link Rivers. The navigable water network in the British Isles grew as the demand for industrial transport increased. It grew rapidly at first, and became an almost completely connected network covering the south, Midlands, and parts of the North of England and Wales. There were canals in Scotland, but they were not connected to the English canals or, generally, to each other (the main exception being the Monkland Canal, the Union Canal and the Forth and Clyde Canal which connected the River Clyde and Glasgow to the River Forth and Edinburgh). As building techniques improved, older canals were improved by straightening, Embankments, cuttings, tunnels, aqueducts, inclined planes, and boat lifts, which together snipped many miles and locks, and therefore hours and cost, from journeys. However, there was often fierce opposition to the building.



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WHAT ARE THE DIFFERENT KINDS OF BRIDGES?


The earliest bridges were probably tree trunks across streams or flat slabs of rock. Gradually, people learned to span wider rivers and ravines by supporting the bridge in the middle. Since then, engineers have devised ways of spanning very wide distances.



There are many different types of bridges although typically their structures can be traced back to one of the seven main types. It is the way in which the vertical/horizontal stresses are managed which dictates the structure of different bridges. In some cases the deck area will be the load-bearing element while in others it will be the towers. There are also designs that transmit tension through bridge cables which allow a degree of flexibility for different terrains.



Beam Bridge



A beam bridge is one of the simplest types of bridge. A perfect example being a basic log bridge – something you may see while out on a country walk. The deck area traditionally consists of wood plank or stone slabs (often referred to as a clapper bridge). These are supported either side by two beams running between abutments/piers. Very often you will find other beams, positioned in between the main beams, offering additional support and stability. The area over which people or vehicles travel will be a simple decking positioned vertically across the underlying beams. This is often referred to as a “simply supported” structure. There is no transfer of stress which you see in arch structures and other types of bridges.



Truss Bridge



The truss bridge has been around for literally centuries and is a load-bearing structure which incorporates a truss in a highly efficient yet very simple design. You will notice an array of different variations of the simple truss bridge but they all incorporate triangular sections. The role of these triangular elements is important because they effectively absorb tension and compression to create a stressed structure able to accommodate dynamic loads. This mixture of tension and compression ensures the structure of the bridge is maintained and the decking area remains uncompromised even in relatively strong winds.



Cantilever Bridge



When the first cantilever bridge was designed it was seen as a major engineering breakthrough. The bridge works by using cantilevers which may be simple beams or trusses. They are made from pre-stressed concrete or structural steel when used to accommodate traffic. When you consider that the horizontal beams making up the cantilever arm are only supported from one side it does begin to sound a little dangerous. However, the two cantilever arms are connected by what is known as the “suspended span” which is effectively a centrepiece which has no direct support underneath. The bridge load is supported through diagonal bracing with horizontal beams as opposed to typical vertical bracing. Extremely safe and very secure, the design of cantilever bridges is one which still lives on today.



Suspension Bridges



The structure of a stereotypical suspension bridge looks very simple but the design is extremely effective. The deck of the suspension bridge is the load-bearing element of the structure. This is held in place by vertical suspenders which support the cables. The suspension cables extend out beyond each side of the bridge and are anchored firmly into the ground. It will depend upon the size of the bridge but a number of towers will be installed to hold up the suspension cables. Any load applied to the bridge is transformed into tension across the suspension cables which are the integral part of the structure. As there is some “give” in the suspension cables this can translate into slight, but measured, bridge movement in difficult weather conditions.



Cable stayed bridge



A cable stayed bridge is dependent upon towers/pylons which are the load-bearing element of the structure. Cables are connected from the pylons to the deck below. Either directly from the top of the tower or at different points of the column. When connected at different points of the column this creates a fan like pattern. This is the feature many people associate with cable stayed bridges. This type of structure tends to be used for distances greater than those achieved with a cantilever bridge design but less than a suspension bridge. One of the main issues with this type of bridge is that the central connection of the cables can place horizontal pressure on the deck. Therefore, the deck structure needs to be reinforced to withstand these ongoing pressures.



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WHO WERE THE FIRST GREAT ROAD-BUILDERS?


From the earliest times, humans and animals have created track ways along well-used routes, but it was the Romans who were the first to set about road-building in a systematic manner. The Roman Empire stretched from North Africa to Scotland. In order to govern successfully, the occupying forces needed to be able to reach trouble spots quickly. Roman roads were built so that armies could march rapidly for hundreds of miles.



A top level of paving stones gave a smooth surface for carts and marching armies. Roman roads were made in layers. First the route was cleared of large stones and boulders. Then the bed of the road was levelled with sand. The Romans tried to build straight roads as far as possible. Straight roads were easier to march along and reduced the risk of ambush, as the view was clear in both directions.



Roman road system outstanding transportation network of the ancient Mediterranean world, extending from Britain to the Tigris-Euphrates river system and from the Danube River to Spain and northern Africa. In all, the Romans built 50,000 miles (80,000 km) of hard-surfaced highway, primarily for military reasons.



The first of the great Roman roads, the Via Appia (Appian Way), begun by the censorAppius Claudius Caecus in 312 BCE, originally ran southeast from Rome 162 miles (261 km) to Tarentum (now Taranto) and was later extended to the Adriatic coast at Brundisium (now Brindisi). The Long Branch running through Calabria to the Straits of Messina was known as the Via Popilia. By the beginning of the 2nd century BCE, four other great roads radiated from Rome: the Via Aurelia, extending northwest to Genua (Genoa); the Via Flaminia, running north to the Adriatic, where it joined the Via Aemilia, crossed the Rubicon, and led northwest; the Via Valeria, east across the peninsula by way of Lake Fucinus (Conca del Fucino); and the Via Latina, running southeast and joining the Via Appia near Capua. Their numerous feeder roads extending far into the Roman provinces led to the proverb “All roads lead to Rome.”



The Roman roads were notable for their straightness, solid foundations, cambered surfaces facilitating drainage, and use of concrete made from pozzolana (volcanic ash) and lime. Though adapting their technique to materials locally available, the Roman engineers followed basically the same principles in building abroad as they had in Italy. In 145 BCE they began the Via Egnatia, an extension of the Via Appia beyond the Adriatic into Greece and Asia Minor, where it joined the ancient Persian Royal Road.



In northern Africa the Romans followed up their conquest of Carthage by building a road system that spanned the south shore of the Mediterranean. In Gaul they developed a system centred on Lyon, whence main roads extended to the Rhine, Bordeaux, and the English Channel. In Britain the purely strategic roads following the conquest were supplemented by a network radiating from London. In Spain, on the contrary, the topography of the country dictated a system of main roads around the periphery of the peninsula, with secondary roads developed into the central plateaus.



The Roman road system made possible Roman conquest and administration and later provided highways for the great migrations into the empire and a means for the diffusion of Christianity. Despite deterioration from neglect, it continued to serve Europe throughout the Middle Ages, and many fragments of the system survive today.



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HOW DOES A SPACESUIT WORK?


A spacesuit is all that stands between an astronaut on a space walk and the emptiness of space. It must supply all his or her needs. There is no breathable atmosphere in space, so a spacesuit supplies oxygen to the astronaut.



Most spacesuits have very specific purposes. First and foremost, they must keep the wearer alive. They serve—in actuality—as individual custom spaceships of a sort, designed for considerably differing environments.



Today, the United States “sports” two specific space suits. One, the Assured Crew Escape System (ACES) suit, is the bright orange contraption familiar to many through viewing shuttle launches on television. Visible during the crew’s “waving walkout” to the Astros Van and their subsequent trip to the launch pad, they are no longer needed with the ending of the space shuttle program (boo hiss!). The suits are now being evaluated for use with future programs—including NASA ’s Orion capsule development—and modified capability to perform spacewalks in the event of a capsule emergency need (e.g., a solar panel that won’t deploy).



Designed to protect the crew only during the ascent (liftoff) and entry (coming back to earth) phases of flight, the ACES suit’s essence was to provide an oxygen source (although a brief one of about 10 minutes) and helmet-suited pressurization for a relatively short period of time, in hopes of enabling the crew to parachute to safety in the event of a bailout emergency. Note that this very purpose went unfulfilled during the Columbia (2003) tragedy and was not even available during Challenger (1986). In fact, the Challenger disaster was one of the key reasons for the original development of this type of spacesuit.



The spacewalking suit, also known as the Extra-Vehicular Activity (EVA) suit, is easily recognizable to even the most casual space buff. Bright white, with identifying stripes of solid, dashed, and angled/hashed red and white, this suit truly was an astronaut’s spaceship. Worn outside of a vehicle while working in the vacuum of outer space, this suit’s design was a bit more extravagant than that of the ACES.



Within the helmet, headphones and a microphone enable the astronaut to communicate with crew members and mission control. All the joins in the spacesuit must be absolutely airtight. Inside, the spacesuit is pressurized, like a deep-sea diver’s suit. A specially treated dark visor protects the astronaut’s eyes from the glare of the Sun, while lights can illuminate dark areas.



A camera may be fixed to the astronaut’s shoulder, so that other crew members and the ground crew can watch what is being done. The temperature, pressure and oxygen levels inside the suit are monitored by a control pack on the astronaut’s front or back. Under the outer suit, a body suit contains pipes through which cool liquid flows to protect the astronaut from the heat of the Sun. The visor and outer layer of the spacesuit must be tough enough not to be torn or cracked by tiny meteorites that may bounce off the astronaut.



Suits are made of artificial materials that offer maximum protection, such as nylon, Kevlar and Dacron. The astronaut is completely sealed within his or her suit, so urine is collected inside for disposal later! On Earth, a spacesuit can be as difficult to walk in as a suit of armour, but in the weightlessness of space, the pull of gravity is not a consideration.



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WHAT IS THE SPACE SHUTTLE USED FOR?


The space shuttle has many uses and, because it is reusable, has made it possible to pursue some space activities that would otherwise have been too expensive. It is used to launch satellites and to make repairs to existing satellites. The shuttle can also be used as a laboratory, in which to carry out experiments that are only possible in zero gravity.



The space shuttle was NASA’s space transportation system. It carried astronauts and cargo to and from Earth orbit. The first space shuttle flight took place April 12, 1981. The shuttle made its final landing July 21, 2011. During those 30 years, the space shuttle launched on 135 missions.



The space shuttle carried as many as seven astronauts at a time to and from space. In all, 355 people flew on the shuttle. Some of them flew more than one time. During its history, the space shuttle flew many different types of missions. It launched satellites and served as an orbiting science laboratory. Its crews repaired and improved other spacecraft, such as the Hubble Space Telescope. The shuttle also flew missions for the military. On its later missions, the space shuttle was mostly used to work on the International Space Station.



The space shuttle had three main parts. The first part was the orbiter. The orbiter was the large, white space plane where the crew lived and worked. It was the only part of the shuttle that flew into orbit. The orbiter also had a payload bay for carrying cargo into orbit. Five different orbiters took turns flying into space. The second part of the shuttle was the external tank. This was the large orange fuel tank that was attached to the bottom of the orbiter for launch. The third part was actually two pieces. A pair of white solid rocket boosters provided most of the thrust for the first two minutes of a shuttle launch. The solid rocket boosters were long and thin.



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HOW DO ASTRONAUTS MOVE OUTSIDE THE SHUTTLE?


Astronauts outside the shuttle are encumbered by a heavy spacesuit, but this is not really a problem in weightless conditions. Controlled movement is more difficult, however. Astronauts wear a unit called a manned maneuvering unit (MMU) on their backs. This is fuelled by nitrogen and is rechargeable in the shuttle. Several small thrusters allow the astronaut to move in all directions.



The process leading up to a spacewalk takes almost an entire day, and it's not because of the many items that make up an astronaut’s suit. The main reason for this is because astronauts need time to go through decompression, the same procedure cave divers use when returning from the depths of the ocean to the surface of the water.



To allow maximum mobility and maximum protection from the lack of pressure in space, a spacesuit is pressurized at 29.6 kilopascals during a spacewalk, about one third of the pressure experienced by the crew inside the spacecraft. Astronauts also have to breathe in pure oxygen, because the amount of oxygen in air at such a low pressure isn't enough.



Now, if an astronaut simply donned a space suit in 15 minutes and promptly exited an airlock, he or she would go through decompression sickness, or "the bends" -- the same thing scuba divers experience if they're exposed to a rapid drop in external pressure by ascending too quickly. The bends causes expanded nitrogen gas bubbles in the bloodstream to escape too quickly, and joint pain, dizziness, cramps, paralysis and even death can follow.



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CAN ANY HUMAN STRUCTURE BE SEEN FROM SPACE?


The Great Wall, which stretches for over 3640km (2150 miles) across China, is the only human structure that can be seen from space.



It has become a space-based myth. The Great Wall of China, frequently billed as the only man-made object visible from space, generally isn't, at least to the unaided eye in low Earth orbit. It certainly isn't visible from the Moon. You can, though, see a lot of other results of human activity.



Expedition 10 photo showing Great Wall of ChinaThe visible wall theory was shaken after China's own astronaut, Yang Liwei, said he couldn’t see the historic structure. There was even talk about rewriting textbooks that espouse the theory, a formidable task in the Earth’s most populous nation. The issue surfaced again after photos taken by Leroy Chiao from the International Space Station were determined to show small sections of the wall in Inner Mongolia about 200 miles north of Beijing.



Taken with a 180mm lens and a digital camera last Nov. 24, it was the first confirmed photo of the wall. A subsequent Chiao photo, taken Feb. 20 with a 400mm lens, may also show the wall.



The photos by Chiao, commander and NASA ISS science officer of the 10th Station crew, were greeted with relief and rejoicing by the Chinese. One was displayed prominently in the nation's newspapers.




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WHY DOES A ROCKET HAVE STAGES?


A rocket needs enormous power to escape from the Earth’s gravity. The velocity required to achieve this is called the escape velocity, which is about 49,000km/h (29,000mph). The rocket’s power comes from burning liquid hydrogen and oxygen. Each stage of a rocket is a fuel tank, which is jettisoned when its fuel is used up. After all, carrying an empty fuel tank will only use up more fuel? Only the top stage of the rocket, called the payload, makes the whole journey and brings the crew back to Earth.



The study of rockets is an excellent way for students to learn the basics of forces and the response of an object to external forces. All rockets use the thrust generated by a propulsion system to overcome the weight of the rocket. For full scale satellite launchers, the weight of the payload is only a small portion of the lift-off weight. Most of the weight of the rocket is the weight of the propellants. As the propellants are burned off during powered ascent, a larger proportion of the weight of the vehicle becomes the near-empty tankage and structure that was required when the vehicle was fully loaded. In order to lighten the weight of the vehicle to achieve orbital velocity, most launchers discard a portion of the vehicle in a process called staging. There are two types of rocket staging, serial and parallel.



In serial staging, there is a small, second stage rocket that is placed on top of a larger first stage rocket. The first stage is ignited at launch and burns through the powered ascent until its propellants are exhausted. The first stage engine is then extinguished, the second stage separates from the first stage, and the second stage engine is ignited. The payload is carried atop the second stage into orbit. Serial staging was used on the Saturn V moon rockets. The Saturn V was a three stage rocket, which performed two staging maneuvers on its way to earth orbit. The discarded stages of the Saturn V were never retrieved. The other type of staging is called parallel staging.



In parallel staging, several small first stages are strapped onto to a central sustainer rocket. At launch, all of the engines are ignited. When the propellants in the strap-ons are extinguished, the strap-on rockets are discarded. The sustainer engine continues burning and the payload is carried atop the sustainer rocket into orbit. Parallel staging is used on the Space Shuttle. The discarded solid rocket boosters are retrieved from the ocean, re-filled with propellant, and used again on the Shuttle.



Some launchers, like the Titan III's and Delta II's, use both serial and parallel staging. The Titan III has a liquid-powered; two stage Titan II for a sustainer and two solid rocket strap-ons at launch. After the solids are discarded, the sustainer engine of the Titan II burns until its fuel is exhausted. Then the second stage of the Titan II is burned, carrying the payload to orbit. The Titan III is another example of a three stage rocket. "Serial" brings the rocket back to its original serial configuration and "Parallel" brings back a parallel configuration.



While they cannot fly all the way to orbit, there are two stage model rocket kits available. You can study the flight characteristics of a two stage model rocket by using the Rocket-Modeler II simulation program. And you can use the Circular Orbit simulation program to investigate the velocity and altitude requirements for specific orbit.




HOW CAN THE SPACE SHUTTLE BE USED OVER AND OVER AGAIN?


At lift-off, the space shuttle has two rocket boosters. These are jettisoned when the shuttle reaches a height of 43km (27 miles). The shuttle usually remains in orbit around the Earth for about seven days, although it can continue for 30 days. When it returns to Earth, the shuttle lands on a runway, in a similar way to an ordinary aircraft. The rocket boosters are reattached to it, so that it is ready for another mission.



Space shuttle, also called Space Transportation System, partially reusable rocket-launched vehicle designed to go into orbit around Earth, to transport people and cargo to and from orbiting spacecraft, and to glide to a runway landing on its return to Earth’s surface that was developed by the U.S. National Aeronautics and Space Administration (NASA). Formally called the Space Transportation System (STS), it lifted off into space for the first time on April 12, 1981, and made 135 flights until the program ended in 2011.



The U.S. space shuttle consisted of three major components: a winged orbiter that carried both crew and cargo; an external tank containing liquid hydrogen (fuel) and liquid oxygen (oxidizer) for the orbiter’s three main rocket engines; and a pair of large, solid-propellant, strap-on booster rockets. At liftoff the entire system weighed 2 million kilograms (4.4 million pounds) and stood 56 metres (184 feet) high. During launch the boosters and the orbiter’s main engines fired together, producing about 31,000 kilonewtons (7 million pounds) of thrust. The boosters were jettisoned about two minutes after liftoff and were returned to Earth by parachute for reuse. After attaining 99 percent of its orbital velocity, the orbiter had exhausted the propellants in the external tank. It released the tank, which disintegrated on reentering the atmosphere. Although the orbiter lifted off vertically like an expendable rocket launcher, it made an unpowered descent and landing similar to a glider.



The space shuttle could transport satellites and other craft in the orbiter’s cargo bay for deployment in space. It also could rendezvous with orbiting spacecraft to allow astronauts to service, resupply, or board them or to retrieve them for return to Earth. Moreover, the orbiter could serve as a space platform for conducting experiments and making observations of Earth and cosmic objects for as long as about two weeks. On some missions it carried a European-built pressurized facility called Spacelab, in which shuttle crew members conducted biological and physical research in weightless conditions.



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WHICH PLANES CAN LAND ON WATER?


Seaplanes and flying boats have floats instead of wheels, so that they can land on water. In the 1930s, flying boats were often larger and more luxurious than ordinary aircraft, as they could be made larger without the expense of creating longer runways at airports around the world. Instead, they took off and landed at sea, taxiing in and out of existing harbours.



In aviation, a water landing is, in the broadest sense, an aircraft landing on a body of water. Some aircraft such as floatplanes land on water as a matter of course. The phrase “water landing” is also used as a euphemism for crash-landing into water an aircraft not designed for the purpose, an event formally termed ditching. In this case, the flight crew knowingly makes a controlled emergency landing on water. Ditching of commercial aircraft is a rare occurrence.



Seaplanes, flying boats, and amphibious aircraft are designed to take off and alight on water. Alighting can be supported by a hull-shaped fuselage and/or pontoons. The availability of a long effective runway was historically important on lifting size restrictions on aircraft, and their freedom from constructed strips remains useful for transportation to lakes and other remote areas. The ability to loiter on water is also important for marine rescue operations and fire-fighting. One disadvantage of water alighting is that it is dangerous in the presence of waves. Furthermore, the necessary equipment compromises the craft's aerodynamic efficiency and speed.



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WHAT IS AN AIRSHIP?


An airship is a cigar-shaped balloon, filled with a gas. Nowadays, this is usually helium, as it cannot catch fire, unlike the hydrogen used in earlier airships. Beneath the balloon, a cabin (often called a gondola) and engines are suspended. In the 1930s, the Germans developed airships called Zeppelins, although the tragic crash of the Hindenburg in the USA in 1937 really spelled the end of the age of the airship.



Airship, also called dirigible or dirigible balloon, a self-propelled lighter-than-air craft. Three main types of airships, or dirigibles (from French diriger, “to steer”), have been built: nonrigids (blimps), semirigids, and rigids. All three types have four principal parts: a cigar-shaped bag, or balloon, that is filled with a lighter-than-air gas; a car or gondola that is slung beneath the balloon and holds the crew and passengers; engines that drive propellers; and horizontal and vertical rudders to steer the craft. Nonrigids are simply balloons with cars attached by cables; if the gas escapes, the balloon collapses. Semirigids likewise depend on the internal gas to maintain the balloon’s shape, but they also have a structural metal keel that extends longitudinally along the balloon’s base and supports the car. Rigids consist of a light framework of aluminum-alloy girders that is covered with fabric but is not airtight. Inside this framework is a number of gas-filled balloons, each of which can be filled or emptied separately; rigids keep their shape whether they are filled with gas or not.



The usual gases used for lifting airships are hydrogen and helium. Hydrogen is the lightest known gas and thus has great lifting capacity, but it is also highly flammable and has caused many fatal airship disasters. Helium is not as buoyant but is far safer than hydrogen because it does not burn. The gas-containing envelopes of early airships used cotton fabric impregnated with rubber, a combination that was eventually superseded by synthetic fabrics such as neoprene and Dacron.



The first successful airship was constructed by Henri Giffard of France in 1852. Giffard built a 160-kilogram (350-pound) stem engine capable of developing 3 horsepower, sufficient to turn a large propeller at 110 revolutions per minute. To carry the engine weight, he filled a bag 44 metres (144 feet) long with hydrogen and, ascending from the Paris Hippodrome, flew at a speed of 10 km (6 miles) per hour to cover a distance of about 30 km (20 miles).



In 1872 a German engineer, Paul Haenlein, first used an internal-combustion engine for flight in an airship that used lifting gas from the bag as fuel. In 1883 Albert and Gaston Tissandier of France became the first to successfully power an airship using an electric motor. The first rigid airship, with a hull of aluminum sheeting, was built in Germany in 1897. Alberto Santos-Dumont, a Brazilian living in Paris, set a number of records in a series of 14 nonrigid gasoline-powered airships that he built from 1898 to 1905.




Picture Credit : Google



HOW DO AIR TRAFFIC CONTROLLERS COMMUNICATE WITH PILOTS?


Air traffic controllers have screens on which they can see the planes in their sector. It is their job to see that planes are kept safely apart and guided appropriately during take-off and landing. When aeroplanes are near enough, the air traffic controllers can speak to them directly, but they cannot be expected to speak all the languages of international pilots. For this reason, to make communications as safe and clear as possible, all instructions and discussions take place in English all over the world.



Air traffic controllers use an aircraft’s registration mark when calling it by radio. As one letter can sound rather like another, words are used instead, each one standing for the letter that begins it.



Until controller-pilot data link communication (CPDLC) comes into widespread use, air traffic control (ATC) will depend upon voice communications that are affected by various factors. Aircraft operators and air traffic management (ATM) providers, like pilots and controllers, are close partners in terms of “productivity” for enhancing the airport and airspace flow capacity; operators and ATM should also be close partners in terms of “safety” or risk management.



Communication between controllers and pilots can be improved by the mutual understanding of each other’s operating environment. This briefing note provides an overview of various factors that may affect pilot-controller communication. It may be used to develop a company awareness program for enhancing pilot-controller communications.



Picture Credit : Google