A spacecraft is a vehicle or machine designed to fly in outer space. Spacecraft are used for a variety of purposes, including communications, earth observation, navigation, space colonization, planetary exploration, transportation of humans and cargo. All spacecraft except single-stage-to-orbit vehicles cannot get into space on their own, require a launch vehicle. On a sub-orbital spaceflight, a space vehicle enters space and returns to the surface, without having gained sufficient energy or velocity to make a full orbit of the Earth. For orbital spaceflights, spacecraft enter closed orbits around the Earth or around other celestial bodies. Spacecraft used for human spaceflight carry people on board as crew or passengers from start or on orbit only, whereas those used for robotic space missions operate either autonomously or telerobotically. Robotic spacecraft used to support scientific research are space probes. Robotic spacecraft that remain in orbit around a planetary body are artificial satellites.
To date, only a handful of interstellar probes, such as Pioneer 10 and 11, Voyager 1 and 2, New Horizons, are on trajectories that leave the Solar System. Orbital spacecraft may be recoverable or not. Most are not. Recoverable spacecraft may be subdivided by method of reentry to Earth into non-winged space capsules and winged spaceplanes. Humanity has achieved space flight but only a few nations have the technology for orbital launches: Russia, the United States, the member states of the European Space Agency, China, Taiwan (National Chung-Shan Institute of Science and Technology, Taiwan National Space Organization, Israel and North Korea. A German V-2 became the first spacecraft when it reached an altitude of 189 km in June 1944 in Peenemünde, Germany. Sputnik 1 was the first artificial satellite, it was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957. The launch ushered in new political, military and scientific developments. Apart from its value as a technological first, Sputnik 1 helped to identify the upper atmospheric layer's density, through measuring the satellite's orbital changes.
It provided data on radio-signal distribution in the ionosphere. Pressurized nitrogen in the satellite's false body provided the first opportunity for meteoroid detection. Sputnik 1 was launched during the International Geophysical Year from Site No.1/5, at the 5th Tyuratam range, in Kazakh SSR. The satellite travelled at 29,000 kilometers per hour, taking 96.2 minutes to complete an orbit, emitted radio signals at 20.005 and 40.002 MHz While Sputnik 1 was the first spacecraft to orbit the Earth, other man-made objects had reached an altitude of 100 km, the height required by the international organization Fédération Aéronautique Internationale to count as a spaceflight. This altitude is called the Kármán line. In particular, in the 1940s there were several test launches of the V-2 rocket, some of which reached altitudes well over 100 km; as of 2016, only three nations have flown crewed spacecraft: USSR/Russia, USA, China. The first crewed spacecraft was Vostok 1, which carried Soviet cosmonaut Yuri Gagarin into space in 1961, completed a full Earth orbit.
There were five other crewed missions. The second crewed spacecraft was named Freedom 7, it performed a sub-orbital spaceflight in 1961 carrying American astronaut Alan Shepard to an altitude of just over 187 kilometers. There were five other crewed missions using Mercury spacecraft. Other Soviet crewed spacecraft include the Voskhod, flown uncrewed as Zond/L1, L3, TKS, the Salyut and Mir crewed space stations. Other American crewed spacecraft include the Gemini spacecraft, Apollo spacecraft, the Skylab space station, the Space Shuttle with undetached European Spacelab and private US Spacehab space stations-modules. China developed, but did not fly Shuguang, is using Shenzhou. Except for the Space Shuttle, all of the recoverable crewed orbital spacecraft were space capsules. Crewed space capsules The International Space Station, crewed since November 2000, is a joint venture between Russia, the United States and several other countries; some reusable vehicles have been designed only for crewed spaceflight, these are called spaceplanes.
The first example of such was the North American X-15 spaceplane, which conducted two crewed flights which reached an altitude of over 100 km in the 1960s. The first reusable spacecraft, the X-15, was air-launched on a suborbital trajectory on July 19, 1963; the first reusable orbital spacecraft, a winged non-capsule, the Space Shuttle, was launched by the USA on the 20th anniversary of Yuri Gagarin's flight, on April 12, 1981. During the Shuttle era, six orbiters were built, all of which have flown in the atmosphere and five of which have flown in space. Enterprise was used only for approach and landing tests, launching from the back of a Boeing 747 SCA and gliding to deadstick landings at Edwards AFB, California; the first Space Shuttle to fly into space was Columbia, followed by Challenger, Discovery and Endeavour. Endeavour was built to replace Challenger when it was lost in January 1986. Columbia broke up during reentry in February 2003; the first automatic reusable spacecraft was the Buran-class shuttle, launched by the USSR on November 15, 1988, although it made only one flight and this was uncrewed.
This spaceplane was designed for a crew and resembled the U
A gasket is a mechanical seal which fills the space between two or more mating surfaces to prevent leakage from or into the joined objects while under compression. Gaskets allow for "less-than-perfect" mating surfaces on machine parts where they can fill irregularities. Gaskets are produced by cutting from sheet materials. Gaskets for specific applications, such as high pressure steam systems, may contain asbestos. However, due to health hazards associated with asbestos exposure, non-asbestos gasket materials are used when practical, it is desirable that the gasket be made from a material, to some degree yielding such that it is able to deform and fill the space it is designed for, including any slight irregularities. A few gaskets require an application of sealant directly to the gasket surface to function properly; some gaskets are made of metal and rely on a seating surface to accomplish the seal. This is typical of some other metal gasket systems; these joints are known as E-con compressive type joints.
Gaskets are made from a flat material, a sheet such as paper, silicone, cork, neoprene, nitrile rubber, polytetrafluoroethylene or a plastic polymer. One of the more desirable properties of an effective gasket in industrial applications for compressed fiber gasket material is the ability to withstand high compressive loads. Most industrial gasket applications involve bolts exerting compression well into the 14 MPa range or higher. Speaking, there are several truisms that allow for better gasket performance. One of the more tried and tested is: "The more compressive load exerted on the gasket, the longer it will last". There are several ways to measure a gasket material's ability to withstand compressive loading; the "hot compression test" is the most accepted of these tests. Most manufacturers of gasket materials will publish the results of these tests. Gaskets come in many different designs based on industrial usage, chemical contact and physical parameters: When a sheet of material has the gasket shape "punched out" of it, it is a sheet gasket.
This can lead to a crude and cheap gasket. In previous times the material was compressed asbestos, but in modern times a fibrous material or matted graphite is used; these gaskets can fill various different chemical requirements based on the inertness of the material used. Non-asbestos gasket sheet is durable, of multiple materials, thick in nature. Material examples are carbon or nitrile synthetic rubber. Applications using sheet gaskets involve corrosive chemicals, steam or mild caustics. Flexibility and good recovery prevent breakage during installation of a sheet gasket; the idea behind solid material is to use metals which cannot be punched out of sheets but are still cheap to produce. These gaskets have a much higher level of quality control than sheet gaskets and can withstand much higher temperatures and pressures; the key downside is that a solid metal must be compressed in order to become flush with the flange head and prevent leakage. The material choice is more difficult. An additional downside is that the metal used must be softer than the flange — in order to ensure that the flange does not warp and thereby prevent sealing with future gaskets.
So, these gaskets have found a niche in industry. Spiral-wound gaskets comprise a mix of filler material; the gasket has a metal wound outwards in a circular spiral with the filler material wound in the same manner but starting from the opposing side. This results in alternating layers of metal; the filler material in these gaskets acts as the sealing element, with the metal providing structural support. These gaskets have proven to be reliable in most applications, allow lower clamping forces than solid gaskets, albeit with a higher cost; the constant seating stress gasket consists of two components. The sealing elements are made from a material suitable to the process fluid and application. Constant seating stress gaskets derive their name from the fact that the carrier ring profile takes flange rotation into consideration. With all other conventional gaskets, as the flange fasteners are tightened, the flange deflects radially under load, resulting in the greatest gasket compression, highest gasket stress, at the outer gasket edge.
Since the carrier ring used in constant seating stress gaskets take this deflection into account when creating the carrier ring for a given flange size, pressure class, material, the carrier ring profile can be adjusted to enable the gasket seating stress to be radially uniform across the entire sealing area. Further, because the sealing elements are confined by the flange faces in opposing channels on the carrier ring, any in-service compressive forces acting on the gasket are transmitted through the carrier ring and avoid any further compression of the sealing elements, thus maintaining a'constant' gasket seating stress while in-service. Thus, the gasket is immune t
Frequency is the number of occurrences of a repeating event per unit of time. It is referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency; the period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals, radio waves, light. For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time. In physics and engineering disciplines, such as optics and radio, frequency is denoted by a Latin letter f or by the Greek letter ν or ν; the relation between the frequency and the period T of a repeating event or oscillation is given by f = 1 T.
The SI derived unit of frequency is the hertz, named after the German physicist Heinrich Hertz. One hertz means. If a TV has a refresh rate of 1 hertz the TV's screen will change its picture once a second. A previous name for this unit was cycles per second; the SI unit for period is the second. A traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. 60 rpm equals one hertz. As a matter of convenience and slower waves, such as ocean surface waves, tend to be described by wave period rather than frequency. Short and fast waves, like audio and radio, are described by their frequency instead of period; these used conversions are listed below: Angular frequency denoted by the Greek letter ω, is defined as the rate of change of angular displacement, θ, or the rate of change of the phase of a sinusoidal waveform, or as the rate of change of the argument to the sine function: y = sin = sin = sin d θ d t = ω = 2 π f Angular frequency is measured in radians per second but, for discrete-time signals, can be expressed as radians per sampling interval, a dimensionless quantity.
Angular frequency is larger than regular frequency by a factor of 2π. Spatial frequency is analogous to temporal frequency, but the time axis is replaced by one or more spatial displacement axes. E.g.: y = sin = sin d θ d x = k Wavenumber, k, is the spatial frequency analogue of angular temporal frequency and is measured in radians per meter. In the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has an inverse relationship to the wavelength, λ. In dispersive media, the frequency f of a sinusoidal wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave: f = v λ. In the special case of electromagnetic waves moving through a vacuum v = c, where c is the speed of light in a vacuum, this expression becomes: f = c λ; when waves from a monochrome source travel from one medium to another, their frequency remains the same—only their wavelength and speed change. Measurement of frequency can done in the following ways, Calculating the frequency of a repeating event is accomplished by counting the number of times that event occurs within a specific time period dividing the count by the length of the time period.
For example, if 71 events occur within 15 seconds the frequency is: f = 71 15 s ≈ 4.73 Hz If the number of counts is not large, it is more accurate to measure the time interval for a predetermined number of occurrences, rather than the number of occurrences within a specified time. The latter method introduces a random error into the count of between zero and one count, so on average half a count; this is called gating error and causes an average error in the calculated frequency of Δ f = 1 2 T
Packaging and labeling
Packaging is the science and technology of enclosing or protecting products for distribution, storage and use. Packaging refers to the process of designing and producing packages. Packaging can be described as a coordinated system of preparing goods for transport, logistics and end use. Packaging contains, preserves, transports and sells. In many countries it is integrated into government, institutional and personal use. Package labeling or labelling is any written, electronic, or graphic communication on the package or on a separate but associated label; the first packages used the natural materials available at the time: baskets of reeds, wooden boxes, pottery vases, ceramic amphorae, wooden barrels, woven bags, etc. Processed materials were used to form packages as they were developed: for example, early glass and bronze vessels; the study of old packages is an important aspect of archaeology. The earliest recorded use of paper for packaging dates back to 1035, when a Persian traveler visiting markets in Cairo noted that vegetables and hardware were wrapped in paper for the customers after they were sold.
The use of tinplate for packaging dates back to the 18th century. The manufacturing of tinplate was the monopoly of Bohemia for a long time. By 1697, John Hanbury had a rolling mill at Pontypool for making "Pontypoole Plates"; the method pioneered there of rolling iron plates by means of cylinders enabled more uniform black plates to be produced than was possible with the former practice of hammering. Tinplate boxes first began to be sold from ports in the Bristol Channel in 1725; the tinplate was shipped from Monmouthshire. By 1805, 80,000 boxes were made and 50,000 exported. Tobacconists in London began packaging snuff in metal-plated canisters from the 1760s onwards. With the discovery of the importance of airtight containers for food preservation by French inventor Nicholas Appert, the tin canning process was patented by British merchant Peter Durand in 1810. After receiving the patent, Durand did, he sold his patent in 1812 to two other Englishmen, Bryan Donkin and John Hall, who refined the process and product and set up the world's first commercial canning factory on Southwark Park Road, London.
By 1813, they were producing the first canned goods for the Royal Navy. The progressive improvement in canning stimulated the 1855 invention of the can opener. Robert Yeates, a cutlery and surgical instrument maker of Trafalgar Place West, Hackney Road, Middlesex, UK, devised a claw-ended can opener with a hand-operated tool that haggled its way around the top of metal cans. In 1858, another lever-type opener of a more complex shape was patented in the United States by Ezra Warner of Waterbury, Connecticut. Set-up boxes were first used in the 16th century and modern folding cartons date back to 1839; the first corrugated box was produced commercially in 1817 in England. Corrugated paper was used as a liner for tall hats. Scottish-born Robert Gair invented the pre-cut paperboard box in 1890—flat pieces manufactured in bulk that folded into boxes. Gair's invention came about as a result of an accident: as a Brooklyn printer and paper-bag maker during the 1870s, he was once printing an order of seed bags, the metal ruler used to crease bags, shifted in position and cut them.
Gair discovered that by cutting and creasing in one operation he could make prefabricated paperboard boxes. Commercial paper bags were first manufactured in Bristol, England, in 1844, the American Francis Wolle patented a machine for automated bag-making in 1852. Packaging advancements in the early 20th century included Bakelite closures on bottles, transparent cellophane overwraps and panels on cartons; these innovations increased improved food safety. As additional materials such as aluminum and several types of plastic were developed, they were incorporated into packages to improve performance and functionality. In 1952, Michigan State University became the first university in the world to offer a degree in Packaging Engineering. In-plant recycling has long been common for producing packaging materials. Post-consumer recycling of aluminum and paper-based products has been economical for many years: since the 1980s, post-consumer recycling has increased due to curbside recycling, consumer awareness, regulatory pressure.
Many prominent innovations in the packaging industry were developed first for military use. Some military supplies are packaged in the same commercial packaging used for general industry. Other military packaging must transport materiel, foods, etc. under severe distribution and storage conditions. Packaging problems encountered in World War II led to Military Standard or "mil spec" regulations being applied to packaging, designated "military specification packaging"; as a prominent concept in the military, mil spec packaging came into being around 1941, due to operations in Iceland experiencing critical losses attributed to bad packaging. In most cases, mil spec packaging solutions are similar to commercial grade packaging materials, but subject to more stringent performance and quality requirements; as of 2003, the packaging sector accounted for about two percent of the gross national product in developed countries. About half of this market was related to food packaging. Packaging and pa
A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke, was preceded by the suction pump, which dates to antiquity; the predecessor to the vacuum pump was the suction pump, known to the Romans. Dual-action suction pumps were found in the city of Pompeii. Arabic engineer Al-Jazari described suction pumps in the 13th century, he said that his model was a larger version of the siphons the Byzantines used to discharge the Greek fire. The suction pump reappeared in Europe from the 15th century. By the 17th century, water pump designs had improved to the point that they produced measurable vacuums, but this was not understood. What was known was that suction pumps could not pull water beyond a certain height: 18 Florentine yards according to a measurement taken around 1635; this limit was a concern to irrigation projects, mine drainage, decorative water fountains planned by the Duke of Tuscany, so the duke commissioned Galileo to investigate the problem.
Galileo advertised the puzzle to other scientists, including Gasparo Berti who replicated it by building the first water barometer in Rome in 1639. Berti's barometer produced a vacuum above the water column; the breakthrough was made by Evangelista Torricelli in 1643. Building upon Galileo's notes, he built the first mercury barometer and wrote a convincing argument that the space at the top was a vacuum; the height of the column was limited to the maximum weight that atmospheric pressure could support. In 1654, Otto von Guericke invented the first vacuum pump and conducted his famous Magdeburg hemispheres experiment, showing that teams of horses could not separate two hemispheres from which the air had been evacuated. Robert Boyle conducted experiments on the properties of vacuum. Robert Hooke helped Boyle produce an air pump which helped to produce the vacuum; the study of vacuum lapsed until 1855, when Heinrich Geissler invented the mercury displacement pump and achieved a record vacuum of about 10 Pa.
A number of electrical properties become observable at this vacuum level, this renewed interest in vacuum. This, in turn, led to the development of the vacuum tube. In the 19th century, Nikola Tesla designed an apparatus that contains a Sprengel pump to create a high degree of exhaustion. Pumps can be broadly categorized according to three techniques:Positive displacement pumps use a mechanism to expand a cavity, allow gases to flow in from the chamber, seal off the cavity, exhaust it to the atmosphere. Momentum transfer pumps called molecular pumps, use high speed jets of dense fluid or high speed rotating blades to knock gas molecules out of the chamber. Entrapment pumps capture gases in a adsorbed state; this includes cryopumps and ion pumps. Positive displacement pumps are the most effective for low vacuums. Momentum transfer pumps in conjunction with one or two positive displacement pumps are the most common configuration used to achieve high vacuums. In this configuration the positive displacement pump serves two purposes.
First it obtains a rough vacuum in the vessel being evacuated before the momentum transfer pump can be used to obtain the high vacuum, as momentum transfer pumps cannot start pumping at atmospheric pressures. Second the positive displacement pump backs up the momentum transfer pump by evacuating to low vacuum the accumulation of displaced molecules in the high vacuum pump. Entrapment pumps can be added to reach ultrahigh vacuums, but they require periodic regeneration of the surfaces that trap air molecules or ions. Due to this requirement their available operational time can be unacceptably short in low and high vacuums, thus limiting their use to ultrahigh vacuums. Pumps differ in details like manufacturing tolerances, sealing material, flow, admission or no admission of oil vapor, service intervals, tolerance to dust, tolerance to chemicals, tolerance to liquids and vibration. A partial vacuum may be generated by increasing the volume of a container. To continue evacuating a chamber indefinitely without requiring infinite growth, a compartment of the vacuum can be closed off and expanded again.
This is the principle for example the manual water pump. Inside the pump, a mechanism expands a small sealed cavity to reduce its pressure below that of the atmosphere; because of the pressure differential, some fluid from the chamber is pushed into the pump's small cavity. The pump's cavity is sealed from the chamber, opened to the atmosphere, squeezed back to a minute size. More sophisticated systems are used for most industrial applications, but the basic principle of cyclic volume removal is the same: Rotary vane pump, the most common Diaphragm pump, zero oil contamination Liquid ring high resistance to dust Piston pump, fluctuating vacuum Scroll pump, highest speed dry pump Screw pump Wankel pump External vane pump Roots blower called a booster pump, has highest pumping speeds but low compression ratio Multistage Roots pump that combine several stages providing high pumping speed with better compression ratio Toepler pump Lobe pumpThe base pressure of a rubber- and plastic-sealed piston pump system is 1 to 50 kPa, while a scroll pump might reach 10 Pa and a rotary vane oil pump with a clean and empty metallic chamber can achieve 0.1 Pa.
A positive displacement vacuum pump moves the same volume of gas with each cycle, so its pumping s