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Satellite Phones

Satellite Phones

A satellite phone or satphone is a mobile phone that communicates directly with orbiting satellites. Depending on the architecture of a particular system, coverage may include the entire planet, or only specific regions. satellite The mobile equipment, also known as a terminal or earth station, varies widely. A satellite phone handset has a size and weight comparable to that of a late 1980s or early 1990s cell phone, but with a large retractable antenna. These are popular on expeditions into remote areas where terrestrial cellular service is unavailable. A fixed installation, such as used shipboard, may include large, rugged, rack-mounted electronics, and a steerable microwave antenna on the mast that automatically tracks the overhead satellites.

Low Earth orbit

LEO telephones utilizes LEO (low Earth orbit) satellite technology. The advantages include providing worldwide wireless coverage with no gaps. All satellite phones tend to be LEOs. LEO satellites orbit the earth at high speed, low altitude orbits with an orbital time of 70–90 minutes, an altitude of 400–700 miles, and provide coverage cells. Since the satellites are not geosynchronous, they must fly complete orbits and thus further guarantee complete coverage over every area by at least one satellite at all times. Blimps are being considered as satellites.

Satellite phones in pop culture

In the movie Jurassic Park III, Alan Grant loans his satellite phone to Nash. Then, the dinosaur eats him and the phone found in the dinosaur's feces. The satellite phone was also used many times on the show Relic Hunter. The main character, Sydney Fox, would use it to communicate back home when she found interesting relics. Also such phones are said to be difficult tap or trace which makes them a popular favorite for both terrorists and Drug Lords alike.

Mobile phone

A mobile phone, also known as a cell phone, smart phone, mobile, or hand phone, is an electronic telecommunications device with the same basic capability as a conventional fixed line telephone, but which is also entirely portable and is not required to be connected with a wire to the telephone network. Most current mobile phones connect instead to the network using a wireless radio wave transmission technology. The mobile phone communicates via a network of base stations which are in turn linked to the conventional telephone network. In addition to the standard voice function of a telephone, a mobile phone can support many additional services such as SMS for text messaging, packet switching for access to the Internet and MMS for sending and receiving photos and video. Some of the world's largest mobile phone manufacturers include Alcatel, Audiovox, Fujitsu, Kyocera (formerly the handset division of Qualcomm), LG, Motorola, NEC, Nokia, Panasonic (Matsushita Electric), Philips, Sagem, Samsung, Sanyo, Sharp, Siemens, SK Teletech, Sony Ericsson, and Toshiba. There are also specialist communication systems related to, but distinct from mobile phones, such as satellite phones and Professional Mobile Radio. Mobile phones are also distinct from cordless telephones, which generally operate only within a limited range of a specific base station.

Worldwide deployment

Radio phones have a long and varied history that stretches back to the 1950s, with hand-held cellular radio devices being available since 1983. Due to their low establishment costs and rapid deployment, mobile phone networks have since spread rapidly throughout the world, outstripping the growth of fixed telephony. In most of Europe, wealthier parts of Asia and Latin America, Australia, Canada and the US, mobile phones are now widely used, with the majority of the adult, teenage, and even child population owning one. The number of cellphone subscribers in the US has reached over 190 million. At present India and China have the largest growth rates of cellular subscribers in the world. The availability of Prepaid or pay as you go services, where the subscriber does not have to commit to a long term contract, has helped fuel this growth. The mobile phone has become ubiquitous because of the interoperability of mobile phones across different networks and countries. This is due to the equipment manufacturers all working to the same standard, particularly the GSM standard which was designed for Europe-wide interoperability. All European nations and some Asian nations chose it as their sole standard, while in Japan and South Korea another standard, CDMA, was selected.

Mobile phone culture

CDMA handset]] In less than twenty years, mobile phones have gone from being rare and expensive pieces of equipment used by businesses to a pervasive low-cost personal item. In many countries, mobile phones now outnumber land-line telephones, with most adults and many children now owning mobile phones. It is not uncommon for young adults to simply own a mobile phone instead of a land-line for their residence. In some developing countries, where there is little existing fixed-line infrastructure, the mobile phone has become widespread. With high levels of mobile telephone penetration, a mobile culture has evolved, where the phone becomes a key social tool, and people rely on their mobile phone addressbook to keep in touch with their friends. Many people keep in touch using SMS, and a whole culture of "texting" has developed from this. The commercial market in SMS's is growing. Many phones even offer Instant Messenger services to increase the simplicity and ease of texting on phones. Cellular phones in Japan, offering internet capabilities such as NTT DoCoMo's i-mode, offer text messaging via standard email. The mobile phone itself has also become a totemic and fashion object, with users decorating, customizing, and accessorizing their mobile phones to reflect their personality. This has emerged as its own industry. The sale of commercial ringtones exceeded $2.5 billion dollars in 2004 [http://digital-lifestyles.info/display_page.asp?section=distribution&id=1474]. Mobile phone etiquette has become an important issue with mobiles ringing at funerals, weddings, movies and plays. Users often speak at increased volume, with little regard for other people nearby. It has become common practice for places like bookshops, libraries, movie theatres, and houses of worship to post signs prohibiting the use of cell phones, sometimes even installing jamming equipment to prevent them. The US intercity passenger system Amtrak offers a "quiet car" where cellphone use is prohibited, much like the designated non-smoking cars in days of yore. Mobile phone use on aircraft is also prohibited. Cameraphones and videophones that can capture video and take photographs are increasingly being used to cover breaking news. Stories like the London Bombings, the Indian Ocean Tsunami and Hurricane Katrina have been reported on by cameraphone users on news sites like NowPublic and photosharing sites like Flickr. In Japan, cellular phone companies provide immediate notification of earthquakes and other natural disasters to their customers free of charge. In the event of an emergency, disaster response crews can locate trapped or injured people using the signals from their cellular phones; an interactive menu accessible through the phone's internet browser notifies the company if the user is safe or in distress.

Mobile phone features

See main article: Mobile phone features Mobile phones are often packed with features that offer users far more than just the capability to send text messages and make voice calls. These may include internet browsing, music (MP3) playback, personal organisers, email, watch/alarm, built-in cameras, ringtones, security measures (e.g. pin codes), SIM blocks, games, radio, Push to talk, infrared and bluetooth connectivity, and call registers.

Technology

Mobile phones and the network they operate under vary significantly from provider to provider, and even from nation to nation. However, all of them communicate over the air (through electromagnetic radio waves) with a base station (which is a special radio mast or tower designed for the purpose). The phones have a low power transceiver that is typically designed to transmit voice and data up to a few kilometers to where the tower is located. The handset constantly listens for the nearest tower with the strongest signal. Once found, the handset informs that tower of its own unique identifier, and alerts the mobile phone network that it is ready and standing-by to receive telephone calls. This cycle is then repeated as the phone roams around the network and new towers appear in the handset's range. Towers have high power radio transmitters which broadcast their presence, and relay communications to and from the mobile handsets. The tower is connected to the telephone network by a high-capacity link. The base station connects to the operator's backbone network and the wider public telephone network as well as the networks of other mobile phone operators. The dialogue between the handset and the tower is a stream of digitized audio. The technology that achieves this depends on the system which the mobile phone operator has adopted. Some technologies include AMPS for analogue, and TDMA, CDMA, GSM, GPRS and UMTS for digital communications. Each network operator also has a unique radio frequency chosen from a small number of standard frequencies allocated to each technology.

Controversy

Health controversy

See main article: Mobile phone radiation and health As with many new technologies, concerns have arisen about the effects on health from using a mobile telephone. There is a small amount of scientific evidence for an increase in certain types of rare tumors (cancer) in long-time, heavy users. More recently a pan-European study provided significant evidence of genetic damage under certain conditions. Some researchers also report the mobile phone industry has interfered with further research on health risks. So far, however, the World Health Organization Task Force on EMF effects on health has no definitive conclusion on the veracity of these allegations. (see also Electromagnetic radiation hazard). It is generally thought, however, that RF is incapable of producing any more than heating effects, as it is considered non-ionizing radiation; in other words, it lacks the energy to disrupt molecular bonds such as occurs in genetic mutations.

Driving controversy

Another controversial but perhaps more lethal health concern is the correlation with automobile accidents. Several studies have shown that motorists have a much higher risk of collisions and losing control of the vehicle while talking on the mobile telephone simultaneously with driving, even when using "hands-free" systems. One such study conducted by the television show Mythbusters concluded that use of mobile phones while driving poses the same risk as someone operating a vehicle while under the influence of alcohol. Accidents involving a driver being distracted by talking on a mobile phone have begun to be prosecuted as negligence similar to driving while intoxicated. In some jurisdictions, such as Ireland, Japan, Singapore, Brazil, Australia, Austria, the United Kingdom and France, as well as several states in the United States driving while using a mobile phone is illegal, though an exception is often made if the phone is equipped with a handsfree system. In Canada it is banned in Newfoundland (Dec 2002) with fines up to US$180.

Security concerns

Early mobile phones did not have much security designed in. Some problems with these models were "cloning", a variant of identity theft, and "scanning" whereby third parties in the local area could intercept and eaves drop in on calls. Analogue phones could also be listened to on some radio scanners. Although more recent digital systems (such as GSM) have attempted to address these fundamental issues, security problems continue to persist. Vulnerabilities (such as SMS spoofing) have been found in many current protocols that continue to allow the possibility of eavesdropping or cloning.

Future prospects

SMS spoofing] There is a great deal of active research and development into mobile phone technology that is currently underway. Some of the improvements that are being worked on are:
- One difficulty in adapting mobile phones to new uses is form factor. For example, ebooks may well become a distinct device, because of conflicting form-factor requirements — ebooks require large screens, while phones need to be smaller. However, this may be solved using folding e-paper or built-in projectors.
- One function that would be useful in phones is a translation function. Currently it is only available in stand-alone devices, such as Ectaco translators.
- An important area of evolution relates to the Man Machine Interface. New solutions are being developed to create new MMI more easily and let manufacturers and operators experiment new concepts. Examples of companies that are currently developing this technology are [http://www.digitalairways.com/ Digital Airways] with the Kaleido product, [http://www.e-sim.com/ e-sim], [http://www.mobile-arsenal.com.ua/ mobile arsenal], and [http://www.trigenix.com/ Qualcomm] with UIOne for the BREW environment.
- Mobile phones will include various speech technologies as they are being developed. Many phones already have rudimentary speech recognition in a form of voice dialling. However, to support more natural speech recognition and translation, a drastic improvement in the state of technology in these devices is required.
- New technologies are being explored that will utilize the Extended Internet and enable mobile phones to treat a barcode as a URL tag. Phones equipped with barcode reader-enabled cameras will be able to snap photos of barcodes and direct the user to corresponding sites on the Internet. This technology can be extended to RFID tags, or even snapped pictures of company logos. Searches can also be personalized to local areas using a GPS system built in to cell phones. Examples of companies that are currently developing this technology are [http://www.neom.com/ Neomedia] (via [http://www.paperclick.com/ Paperclick]), [http://www.mobot.com/ Mobot] and [http://www.scanbuy.com/ Scanbuy].
- Developments in miniaturised hard disks and flash drives to solve the storage space issue, therefore opening a window for phones to become portable music libraries and players similar to the iPod.
- Developments in podcast software enables mobile phones to become podcast playback devices through existing channels like [http://www.geocities.com/tvhuangsg/mmspodcast/ MMS Podcast], [http://www.geocities.com/tvhuangsg/javacast/ J2ME Podcast] and [http://www.geocities.com/tvhuangsg/mobcast/ AMR-NB Podcast].
- The emergence of integration capabilities with other unlicensed access technologies such as a WiMAX and WLAN, as well as allowing handover between traditional operator networks supporting GSM, CDMA and UMTS to unlicensed mobile networks. The new standard (UMA) has been developed for this.
- Further improvements in battery life will be required. Colour screens and additional functions put increasing demands on the device's power source, and battery developments may not proceed sufficiently fast to compensate. However, different display technologies, such as OLED displays, e-paper or retinal displays, smarter communication hardware (directional antennae, multi-mode and peer-to-peer phones) may reduce power requirements, while new power technologies such as fuel cells may provide better energy capacity.
- Speculative improvements in the future may be inspired by an English team led by James Auger and Jimmy Loizeau who in 2002 developed an implant designed to be inserted into a tooth during dental surgery. This device consists of a radio receiver and transducer, which transmits the sound via bone conduction through the jawbone into the ear. Sound is transmitted via radio waves from another device (presumably a mobile phone) and received by the implant. The implant is currently powered externally, given that no current power source is small enough to fit inside the tooth with it. In addition, the implant was only designed to receive signals, not transmit them. Directly tapping into the inner ear or the auditory nerve is already technologically feasible and will become practical as surgical methods advance.
- New technology in Japan has combined the RFID chip principle into the handset and hooked it up to a network of readers and interfaces. The system, pioneered by NTT Docomo and SonyEricsson, is called Felica and there are around 10,000 convenience stores where one can now use a phone to pay for goods just by 'swiping' it over a flat reader. By charging up a phone with pre-paid cash credits, it can act as a sophisticated mobile-phone wallet. The technology is proving popular and there are now even vending machines that accept this form of payment.
- The delivery of multimedia content including video to mobiles is beginning to become a reality with two main competing standards DMB - Digital Multimedia Broadcasting - and DVB-H - a handset version of the Digital Video Broadcasting standard. These methods avoid swamping the network by using traditional broadcasting.

Terminology

Mobile phone terms

; Brick : A large-sized early handheld mobile phone, such as the Motorola International 3200, nearly the size of a VHS video cassette, with the keypad and microphone on the narrow side. ; Candybar : A housing shape that has no hinges and resembles an oblong candy bar (US). ; Cell phone or cellular telephone : Term used currently in the United States (and in other countries as well during the 1980s) to refer to most mobile phones. It technically applies specifically to mobile phones which use a cellular network. In developing mobile phone technology, American electrical engineers saw the main technical problem as achieving a smooth handoff from one radio antenna to the next. After they gave the name "cell" to the zone covered by each antenna, it was a natural choice for them to apply the term "cellular" to both the technology and the phones that ran on it. ; Clamshell : A phone that opens up to reveal the keypad, microphone, and earpiece; these are typically more compact than other designs. Often called "flip phones". Clamshell phones became very popular in the United States after the introduction of Motorola's StarTAC in 1996. ; Handset: The term handset is used by cell-phone manufacturers to refer to a mobile phone. Also commonly used by industry insiders. ; Handy : Pronounced "Hendi", is a pseudo-anglicism, derived from the term Handy Talkie for a handheld military radio (also known as walkie-talkie), that is used in Austria and Germany for a mobile phone (rare alternative spelling: Händi). In German, the word "Handy" is derived from "handgehaltenes (or hand-held) Telefon." Similarly another pseudo-English term Hand phone is used in East and South Asian countries like South Korea, Malaysia and Singapore. ; Hands free car kit: cell phone accessory use to talk while keeping hands on the steering wheel. ; Mobile phone : A term covering cellular phones, satellite phones and any phones giving wide ranging mobility, used in most English-speaking countries. ; Mobile : Short for 'mobile phone', a term in everyday usage in some English-speaking countries such as the UK. ; Satellite phone : A mobile phone which communicates with a satellite rather than a land-based network. ; Wireless phone : A term that generally refers to a Wi-Fi VoIP phone but is sometimes used by the mobile phone industry to describe mobile phones. ; Ringtone : A song or tune that is played when a cell phone is receiving a call. ; 3G phone : A mobile phone which uses a 3G network, with greater bandwidth allowing faster data downloads and face to face video calling.

Related systems which are not cellphones

; Cordless Phone (Portable Phone) : Cordless phones are standard telephones with radio handsets. Unlike mobile phones, cordless phones use private base stations that are not shared between subscribers. The base station is connected to a land-line. ; Radio Phone : This is an term which covers radios which could connect into the telephone network. These phones may not be mobile, for example, they may require a mains power supply. ; Professional Mobile Radio : Professional mobile radio systems are very similar to cellphone systems and attempts have even been made to use TETRA, the international digital PMR standard, to implement public mobile networks, but normally PMR systems are sufficiently separate from the phone network to not really be considered phones but rather radios.

Terms in other countries

For a list of what mobile phones are called in other countries around the world, see the following article: Mobile phone terms across the world

External links

- [http://electronics.howstuffworks.com/cell-phone.htm How Cell Phones Work] (How Stuff Works)
- [http://www.howardforums.com/ Howard Forums] Forums for cell phone professionals
- [http://www.cellphonehacks.com/ CellPhoneHacks] Mobile phone forum for beginners to experts
- [http://cellwatch.blogspot.com/ Cell Watch] Cell phone trends
- [http://www.isracast.com/tech_news/250705_tech.htm Cell Phone Radiation May cause visual damage] - a possible link between microwave radiation, and different kinds of damage to the visual system was found by a team of researchers from the Technion. Category:Wireless communications Category:Embedded systems Category:Telephony Category:Consumer electronics Category:Mobile telephony standards ko:휴대 전화 ja:携帯電話 zh-min-nan:Hêng-tōng tiān-oē

Satellite

A satellite is any object that orbits another object (which is known as its primary). All masses that are part of the solar system, including the Earth, are satellites either of the Sun, or satellites of those objects, such as the Moon. It is not always a simple matter to decide which is the 'satellite' in a pair of bodies. Because all objects exert gravity, the motion of the primary object is also affected by the satellite. If two objects are sufficiently similar in mass, they are generally referred to as a binary system rather than a primary object and satellite; an extreme example is the 'double asteroid' 90 Antiope. The general criterion for an object to be a satellite is that the center of mass of the two objects is inside the primary object. In popular usage, the term 'satellite' normally refers to an artificial satellite (a man-made object that orbits the Earth or another body). However, scientists may also use the term to refer to natural satellites, or moons. This article is primarily concerned with artificial satellites. See natural satellite for information on moons.

Artificial satellites

History of artificial satellites

natural satellite In May, 1946, the Preliminary Design of an Experimental World-Circling Spaceship stated, "A satellite vehicle with appropriate instrumentation can be expected to be one of the most potent scientific tools of the Twentieth Century. The achievement of a satellite craft would produce repercussions comparable to the explosion of the atomic bomb..." (see: Project RAND) The space age began in 1946, as scientists began using captured German V-2 rockets to make measurements in the upper atmosphere. Before this period, scientists used balloons that went up to 30 km and radio waves to study the ionosphere. From 1946 to 1952, upper-atmosphere research was conducted using V-2s and Aerobee rockets. This allowed measurements of atmospheric pressure, density, and temperature up to 200 km. (see also: magnetosphere, Van Allen radiation belt) The U.S. had been considering launching orbital satellites since 1945 under the Bureau of Aeronautics of the United States Navy. The Air Force's Project RAND eventually released the above report, but did not believe that the satellite was a potential military weapon; rather they considered it to be a tool for science, politics, and propaganda. In 1954, the Secretary of Defense stated, "I know of no American satellite program." Following pressure by the American Rocket Society, the National Science Foundation, and the International Geophysical Year, military interest picked up and in early 1955 the Air Force and Navy were working on Project Orbiter, which involved using a Jupiter C rocket to launch a small satellite called Explorer 1 on January 31, 1958. On July 29, 1955, the White House announced that the U.S. intended to launch satellites by the spring of 1958. This became known as Project Vanguard. On July 31, the Soviets announced that they intended to launch a satellite by the fall of 1957 and on October 4, 1957 Sputnik I was launched into orbit, which triggered the Space Race between the two nations. The largest artificial satellite currently orbiting the earth is the International Space Station, which can sometimes be seen with the unaided human eye.

Types of satellites

Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects. Communications satellites are artificial satellites stationed in space for the purposes of telecommunications using radio at microwave frequencies. Most communications satellites use geosynchronous orbits or near-geostationary orbits, although some recent systems use low Earth-orbiting satellites. Earth observation satellites are satellites specifically designed to observe Earth from orbit, similar to reconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc. (See especially Earth Observing System.) Navigation satellites are satellites which use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few metres in real time. Reconnaissance satellites are Earth observation satellite or communications satellite deployed for military or intelligence applications. Little is known about the full power of these satellites, as governments who operate them usually keep information pertaining to their reconnaissance satellites classified. Solar power satellites are proposed satellites built in high Earth orbit that use microwave power transmission to beam solar power to very large antenna on Earth where it can be used in place of conventional power sources. Space stations are man-made structures that are designed for human beings to live on in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities — instead, other vehicles are used as transport to and from the station. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years. Weather satellites are satellites that primarily are used to monitor the weather and/or climate of the Earth. Miniaturized satellites are satellites of unusually low weights and small sizes. New classifications are used to categorize these satellites: minisatellite (500–200 kg), microsatellite (below 200 kg), nanosatellite (below 10 kg).

Orbit types

Many times satellites are characterized by their orbit. Although a satellite may orbit at almost any height, satellites are commonly categorized by their altitude:
- Low Earth Orbit (LEO: 200 - 1200km above the Earth's surface)
- Medium Earth Orbit (ICO or MEO: 1200 - 35286 km)
- Geosynchronous Orbit (GEO: 35786 km above Earth's surface)
- Geostationary Orbit (GSO: zero inclination geosynchronous orbit)
- High Earth Orbit (HEO: above 35786 km) The following orbits are special orbits that are also used to categorize satellites:
- Molniya orbits
- Heliosynchronous or sun-synchronous orbit
- Polar orbit
- LTO lunar transfer orbit
- Hohmann transfer orbit For this particular orbit type, it is more common to identify the satellite as a spacecraft.
- Supersynchronous orbit or drift orbit - orbit above GEO. Satellites will drift in a westerly direction.
- (GEO + 235 km + (1000 × CR × A/m) km)
- where CR is the solar pressure radiation coefficient (typically between 1.2 and 1.5) and A/m is the aspect area [m²] to dry mass [kg] ratio
- Subsynchronous orbit or drift orbit - orbits close to but below GEO. Used for satellites undergoing station changes in an eastern direction. Satellites can also orbit libration points.

Countries with satellite launch capability

This list includes counties with an independent capability to place satellites in orbit, including production of the necessary launch vehicle. Many more countries have built satellites that were launched with the aid of others. The French and British capabilities are now subsumed by the European Union under the European Space Agency. In 1998, North Korea claimed to have launched a satellite, but this was never confirmed, and widely believed to be a cover for the test launch of the Taepodong-1 missile over Japan (See Kwangmyongsong).

Reference

External links

- [http://science.nasa.gov/Realtime/JPass/20/ J-Pass] NASA site for satellite-watching
- [http://www.stoff.pl Orbitron - Satellite Tracking System] Free satellite tracking software
- [http://ilectric.com/glance/Recreation/Radio/Amateur/Satellite_Tracking/ Satellite Tracking in Recreation Radio Amateur] an excellent link to many links
- [http://www.oosa.unvienna.org UN Office for Outer Space Affairs] ensures all countries benefit from satellites
- [http://www.satellite-service-providers.com/ Satellite Service Providers] Compare and review on top satellite tv, radio and internet service providers] Category:Satellites Category:Unmanned vehicles ko:인공 위성 ja:人工衛星

Cell phone

Worldwide deployment

Mobile phone culture

Mobile phone features

Technology

Controversy

Health controversy

Driving controversy

Security concerns

Future prospects

Terminology

Mobile phone terms

Related systems which are not cellphones

Terms in other countries

For a list of what mobile phones are called in other countries around the world, see the following article: Mobile phone terms across the world

External links

Cellular

- For cellular phones see Mobile phone
- For cellular radio networking in general see cellular network
- For cellular in the meaning of biology, see Cell (biology).
- For the 2004 movie see Cellular (film).

Low Earth orbit

A low Earth orbit (LEO) is an orbit around Earth between the atmosphere and the Van Allen radiation belt, with a low angle of inclination. These boundaries are not firmly defined but are typically around 200 - 1200 km (124 - 726 miles) above the Earth's surface. This is generally below intermediate circular orbit (ICO) and far below geostationary orbit. Orbits lower than this are not stable and will decay rapidly because of atmospheric drag. Orbits higher than this are subject to early electronic failure because of intense radiation and charge accumulation. Orbits with a higher inclination angle are usually called polar orbits. Objects in low earth orbit encounter atmospheric gases in the thermosphere (approximately 80-500 km up) or exosphere (approximately 500 km and up), depending on orbit height. Most manned spaceflights have been in LEO, including all Space Shuttle and various space station missions; the only exceptions have been suborbital test flights such as the early Project Mercury missions and the flights of the X-15 rocket plane (which was not intended to reach LEO), and the Project Apollo missions to the Moon (which went beyond LEO). Most artificial satellites are placed in LEO, where they travel at about 27,400 km/h (8 km/s), making one revolution in about 90 minutes. The primary exception are communication satellites that require geostationary orbit. However, it requires less energy to place a satellite into a LEO and the satellite needs less powerful transmitters for data transfer, so LEO is still used for many communication applications. Because these orbits are not geostationary, a network of satellites is required to provide continuous coverage. Lower orbits also aid remote sensing satellites because of the added detail that can be gained. Remote sensing satellites can also take advantage of sun synchronous LEO orbits at an altitude of about 800km and near polar inclination. ENVISAT is one example of an earth observation satellite that makes use of this special type of LEO. The LEO environment is becoming congested, not least with space debris. The United States Space Command tracks more than 8,000 objects larger than 10cm in LEO. Although gravity in LEO is not much less than on the surface of the Earth (it reduces 1% every 30 km), people and objects in orbit experience weightlessness (see article). Atmospheric and gravity drag associated with launch typically add 1,500-2,000 m/s to the delta-V required to reach normal LEO orbital velocity of 7,800 m/s.

Alternatives

Airships have been proposed to hover above the Earth at an altitude of around 13 miles (20 kilometres) as communication stations, to provide cellular voice and data service. Solar-powered unpiloted aircraft (UAVs) are also proposed for this purpose.

Satellite

Artificial satellites

History of artificial satellites

Types of satellites

Orbit types

Countries with satellite launch capability

Reference

External links

World

:This article is about the World, meaning the Earth. For uses of the specific phrase "The World", see The World (disambiguation) The World (disambiguation)] The World (disambiguation) In English, world is rooted in a compound of the obsolete words were, man, and eld, age; thus, its oldest meaning is "age or life of man". Its primary modern meaning is the planet Earth, especially when capitalized: the World. In this sense, a world map is a map of the surface of the Earth. World can also refer to human population in general or to a distinct group of people.
Physical locations
In other contexts, "world" is sometimes used to mean any planet or moon; for example, Mars and Titan are two worlds within the solar system. "World" is sometimes used to refer to the entire Universe. This is less common now that knowledge of space is more commonplace; however, it is still used vaguely in this sense (as in "the whole wide world"), which it is actually the most frequent sense in philosophy.
Other meanings
World can be used in less literal words; for example, two people with very little in common are "living in two different worlds." The "end of the world" usually means "the end of everything I am familiar with."
- In Christianity the world connotes the fallen and corrupt world order of human society outside the community of believers. The world is frequently cited alongside the flesh and the Devil as a source of temptation that Christians should flee. Monks speak of striving to be "in this world, but not of this world", and the term "worldhood" has been distinguished from "monkhood", the former being the status of merchants, farmers, and others who deal with "worldly" things.
- World can also refer to a fictional setting, for example the world of Star Trek or the world of The Lord of the Rings. See fictional realm.
- In knowledge engineering and knowledge level modeling, a system's world is the knowledge that system has about its environment.
- The term can also be used in a culturally specific context: commentators increasingly refer, for example, to the "Muslim world" as if it were a distinct entity.
- In Native American mythology, the Fifth World is the coming world that will exist after the current world.
- World can refer to WORLD Magazine, the fourth largest newsweekly in the United States.
- In Europe, the word "World" refers to Europe (and sometimes America as well).
First World, Second World, Third World
Europe]] The terms First World, Second World, and Third World were used to divide the nations of Earth into three broad categories. The three terms did not arise simultaneously. After World War II it became common to speak of the capitalist and Communist countries as two major blocs, scarcely using such terms as the "free world" as compared to the "communist bloc". The two "worlds" were not numbered. It was eventually pointed out that there were a great many countries that fit into neither category, and in the 1950s this latter group came to be called the Third World. It then began to seem that there ought to be a "First World" and a "Second World." These latter terms were always much less common. In the context of the Cold War:
- First World refers to nations that were within the Western European and United States' sphere of influence — e.g., the NATO countries of North America and Western Europe, Japan, South Korea, and some of the former British colonies such as Australia, New Zealand, and South Africa.
- Second World referred to nations within the Soviet Union's sphere of influence, principally the Warsaw Pact countries. Besides the Soviet Union proper, most of Eastern Europe was run by satellite governments working closely with Moscow. This term may or may not also refer to Communist countries whose leadership were at odds with Moscow, e.g. China and Yugoslavia. Recently, this term has been used to describe former Third World countries that have experienced too much development to be classified any longer as being a part of the Third World.
- Third World refers to nations within neither sphere of influence, who were often members of the Non-Aligned Movement. They were mostly developing countries, and many of them are located in Africa, Latin America, and Asia. They are often nations that were colonized by another nation in the past. After World War II, the First and Second Worlds struggled to expand their respective spheres of influence to the Third World. The militaries and intelligence services of the United States and the Soviet Union worked both secretly and overtly to influence Third World governments, with mixed success. There were a number of countries which did not fit comfortably into this neat definition of partition, including Switzerland, Sweden, and the Republic of Ireland, which chose to be neutral. Finland was under the Soviet Union's sphere of influence but was not communist, nor was it a member of the Warsaw Pact. Austria was under the United States' sphere of influence, but in 1955, when the country again became a fully independent republic, it did so under the condition that it remained neutral. With the 1991 collapse of the Soviet Union, the term "Second World" largely fell out of use, though the term "Third World" remains popular, mostly as another term for developing countries. The remaining Communist countries either became more isolated from the world economy, as in North Korea and Cuba, or began integrating capitalist concepts such as private enterprise into their societies and forging new trading ties with external capitalist economies, as in Vietnam and China. In more recent use, the term First World refers to developed nations, while Third World, in contrast, refers to developing/undeveloped nations. There is also the less commonly used term Fourth World, often used to refer to nations that lack any national representation at the UN, but that may enjoy representation at UNPO — indigenous peoples living within or across state boundaries. "The World" can also be used to refer to the group of people on the planet earth.
See also

- World economy Category:Culture Category:Geography Category:Universe ja:世界

Speed

:For alternate uses, see special education or speed (disambiguation). Speed (symbol: v) is the rate of motion, or equivalently the rate of change of position, expressed as distance d moved per unit of time t. Speed is a scalar quantity with dimensions distance/time; the equivalent vector quantity to speed is known as velocity. Speed is measured in the same physical units of measurement as velocity, but does not contain the element of direction that velocity has. Speed is thus the magnitude component of velocity. Units of speed include:
- metres per second, (symbol m/s), the SI derived unit
- kilometres per hour, (symbol km/h)
- miles per hour, (symbol mph)
- knots (nautical miles per hour, symbol kt)
- Mach, where Mach 1 is the speed of sound; Mach n is n times as fast. ::Mach 1 = ~343 m/s = ~1235 km/h = ~768 mi/h (see the speed of sound for more detail)
- speed of light in vacuum (symbol c) is one of the natural units ::c = 299,792,458 m/s
- [other important conversions] ::1 m/s = 3.6 km/h ::1 mph = 1.609 km/h ::1 knot = 1.852 km/h = 0.514 m/s Vehicles often have a speedometer to measure the speed. The rate of change of speed with respect to time is termed acceleration.

Average speed

Speed as a physical property represents primarily instantaneous speed. In real life we often use average speed (denoted

\tilde

), which is rate of total distance (or length) and time interval. For example, if you go 60 miles in 2 hours, your average speed during that time is 60/2 = 30 miles per hour, but your instantaneous speed may have varied. In mathematical notation: :

\tilde = \frac.

Instantaneous speed defined as a function of time on interval

[t_0, t_1]

gives average speed:
:

\tilde = \frac

while instant speed defined as a function of distance (or length) on interval

[l_0, l_1]

gives average speed:
:

\tilde = \frac

It is often intuitively expected that going half a distance with speed

v_

and second half with speed

v_

, produce total average speed

\tilde = \frac

. The correct value is

\tilde = \frac

(Note that the first is arithmetic mean while the second is harmonic mean).
Average speed can be derived also from speed distribution function (either in time or on distance): :

v \sim D_t\; \Rightarrow \; \tilde = \int v D_t(v) \, dv

v \sim D_l\; \Rightarrow \; \tilde = \frac

Satellite Phones

Low Earth orbit

Satellite phones in pop culture

See also

Mobile phone

Worldwide deployment

Mobile phone culture

Mobile phone features

Technology

Controversy

Health controversy

Driving controversy

Security concerns

Future prospects

Terminology

Mobile phone terms

Related systems which are not cellphones

Terms in other countries

See also

Integrated devices

External links

Satellite

Artificial satellites

History of artificial satellites

Types of satellites

Orbit types

Countries with satellite launch capability

See also

Reference

External links

Cell phone

Worldwide deployment

Mobile phone culture

Mobile phone features

Technology

Controversy

Health controversy

Driving controversy

Security concerns

Future prospects

Terminology

Mobile phone terms

Related systems which are not cellphones

Terms in other countries

See also

Integrated devices

External links

Cellular

Low Earth orbit

Alternatives

See also

Satellite

Artificial satellites

History of artificial satellites

Types of satellites

Orbit types

Countries with satellite launch capability

See also

Reference

External links

World

Physical locations

Other meanings

First World, Second World, Third World

See also

Speed

Average speed

Cultural sig