:: wikimiki.org ::

Communications Satellite

Communications satellite

A communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites use geosynchronous orbits, Molniya orbits or low Earth orbits. For fixed services, communications satellites provide a technology complementary to that of fiber optic submarine communication cables. For mobile applications, such as communications to ships and planes, for which application of other technologies, such as cable, are impractical or impossible.

History

Early missions

The second satellite to relay communications was Project SCORE in 1958, which used a tape recorder to store and forward voice messages. It was used to send a Christmas greeting to the world from President Eisenhower. NASA launched an Echo satellite in 1960. This 100-foot aluminized Mylar balloon served as a passive reflector for radio communications. Courier 1B, (built by Philco) also was launched in 1960, was the world’s first active repeater satellite. Telstar was the first active, direct relay communications satellite. Belonging to AT&T as part of a multi-national agreement between AT&T, Bell Telephone Laboratories, NASA, the British General Post Office, and the French National PTT (Post Office) to develop satellite communication, it was launched by NASA from Cape Canaveral on July 10, 1962, the first privately sponsored space launch. Telstar was placed in an elliptical orbit (completed once every 2 hours and 37 minutes), rotating at a 45° angle above the equator. An immediate antecedent of the geostationary satellites was Hughes’ Syncom 2, launched on July 26 1963. Syncom 2 revolved around the earth once per day at constant speed, but because it still had north-south motion special equipment was needed to track it.

Geostationary orbits

A satellite in a geostationary orbit appears to be in a fixed position to an earth-based observer. A geostationary satellite revolves around the earth at a constant speed once per day over the equator. The geostationary orbit is useful for communications applications because ground based antennae, which must be directed toward the satellite, can operate effectively without the need for expensive equipment to track the satellite’s motion. Especially for applications that require a large number of ground antennae (such as direct TV distribution), the savings in ground equipment can more than justify the extra cost and onboard complexity of lifting a satellite into the relatively high geostationary orbit. The concept of the geostationary communications satellite was first proposed by Arthur C. Clarke, building on work by Konstantin Tsiolkovsky and on the 1929 work by Herman Potočnik (writing as Herman Noordung) Das Problem der Befahrung des Weltraums - der Raketen-motor. In October 1945 Clarke published an article titled “[http://www.lsi.usp.br/~rbianchi/clarke/ACC.ETRelaysFull.html Extra-terrestrial Relays]” in the British magazine Wireless World. The article described the fundamentals behind the deployment of artificial satellites in geostationary orbits for the purpose of relaying radio signals. Thus Arthur C. Clarke is often quoted as being the inventor of the communications satellite. The first geostationary communications satellite was Anik 1, a Canadian satellite launched in 1972. The United States launched their own geostationary communication satellites afterward, with Western Union launching their Westar 1 satellite in 1974, and RCA Americom (later GE Americom, now SES Americom) launching Satcom 1 in 1975. It was Satcom 1 that was instrumental in helping early cable TV channels such as WTBS (now TBS Superstation), HBO, CBN (now ABC Family), and The Weather Channel become successful, because these channels distributed their programming to all of the local cable TV headends using the satellite. Additionally, it was the first satellite used by broadcast TV networks in the United States, like ABC, NBC, and CBS, to distribute their programming to all of their local affiliate stations. The reason that Satcom 1 was so widely used is that it had twice the communications capacity of Westar 1 (24 transponders as opposed to Westar 1’s 12), which resulted in lower transponder usage costs. By 2000 Hughes Space and Communications (now Boeing Satellite Systems) had built nearly 40 percent of the satellites in service worldwide. Other major satellite manufacturers include Space Systems/Loral, Lockheed Martin (owns former RCA Astro Electronics/GE Astro Space business), Alcatel Space and EADS Astrium.

Low-Earth-orbiting satellites

A low Earth orbit typically is a circular orbit about 150 kilometres above the earth’s surface and, correspondingly, a period (time to revolve around the earth) of about 90 minutes. Because of their low altitude, these satellites are only visible from within a radius of roughly 1000 kilometres from the sub-satellite point. In addition, satellites in low earth orbit change their position relative to the ground position quickly. So even for local applications, a large number of satellites are needed if the mission requires uninterrupted connectivity. Low earth orbiting satellites are less expensive to position in space than geostationary satellites and, because of their closer proximity to the ground, require lower signal strength. So there is a trade off between the number of satellites and their cost. In addition, there are important differences in the onboard and ground equipment needed to support the two types of missions. A group of satellites working in concert thus is known as a satellite constellation. Two such constellations which were intended for provision for hand held telephony, primarily to remote areas, were the Iridium and Globalstar. The Iridium system has 66 satellites. Another LEO satellite constellation, with backing from Microsoft entrepreneur Paul Allen, was to have as many as 720 satellites. It is also possible to offer discontinuous coverage using a low Earth orbit satellite capable of storing data received while passing over one part of Earth and transmitting it later while passing over another part. This will be the case with the CASCADE system of Canada’s CASSIOPE communications satellite.

Molniya satellites

As mentioned, geostationary satellites are constrained to operate above the equator. As a consequence, they are not always suitable for providing services at high latitudes: for at high latitudes a geostationary satellite may appear low on (or even below) the horizon, affecting connectivity and causing multipathing (interference caused by signals reflecting off the ground into the ground antenna). The first satellite of Molniya series was launched on April 23, 1965 and was used for experimental transmission of TV signal from Moscow uplink station to downlink stations, located in Russian Far East, in Khabarovsk, Magadan and Vladivostok. In November of 1967 Soviet engineers created an unique system of national TV network of satellite television, called Orbita, that was based on Molniya satellites. Molniya orbits can be an appealing alternative in such cases. The Molniya orbit is highly inclined, guaranteeing good elevation over selected positions during the northern portion of the orbit. (Elevation is the extent of the satellite’s position above the horizon. Thus a satellite at the horizon has zero elevation and a satellite directly overhead has elevation of 90 degrees). Furthermore, the Molniya orbit is so designed that the satellite spends the great majority of its time over the far northern latitudes, during which its ground footprint moves only slightly. Its period is one half day, so that the satellite is available for operation over the targeted region for eight hours every second revolution. In this way a constellation of three Molniya satellites (plus in-orbit spares) can provide uninterrupted coverage. Molniya satellites are typically used for telephony and TV services over Russia. Another application is to use them for mobile radio systems (even at lower latitudes) since cars travelling through urban areas need access to satellites at high elevation in order to secure good connectivity, e.g. in the presence of tall buildings.

Applications

Telephony

Russia, used for DTH television broadcasting in Europe]] The first and still, arguably, most important application for communication satellites is in international satellite. An analogous path is then followed on the downlink. In contrast, mobile telephones (to and from ships and airplanes) must be directly connected to equipment to uplink the signal to the satellite, as well as being able to ensure satellite pointing in the presence of disturbances, such as waves onboard a ship. Hand held telephony (cellular phones) used in urban areas do not make use of satellite communications. Instead they have access to a ground based constellation of receiving and retransmitting stations.

Television and Radio

There are two types of satellites used for television and radio:
- Direct Broadcast Satellite (DBS), and
- Fixed Service Satellite (FSS). A direct broadcast satellite is a communications satellite that transmits to small DBS satellite dishes (usually 18" to 24" in diameter). Direct broadcast satellites generally operate in the upper portion of the K_u band. DBS technology is used for DTH-oriented (Direct-To-Home) satellite tv services, such as DirecTV and Dish Network in the United States, ExpressVu in Canada, and Sky Digital in the UK. Fixed Service Satellites use the C band, and the lower portions of the K_u bands. They are normally used for broadcast feeds to and from television networks and local affiliate stations (such as program feeds for network and syndicated programming, live shots, and backhauls), as well as being used for distance learning by schools & universities, business television (BTV), videoconferencing, and general commercial telecommunications. FSS satellites are also used to distribute national cable channels to cable TV headends. FSS satellites differ from DBS satellites in that they have a lower RF power output than the latter, requiring a much larger dish for reception (3 to 8 feet in diameter for K_u band, and 12 feet on up for C band). FSS satellite technology was also originally used for DTH satellite TV from the late 1970s to the early 1990s in the USA in the form of TVRO (TeleVision Receive Only) receivers and dishes (a.k.a. big-dish, or more pejoratively known as big ugly dish, systems). It was also used in its K_u band form for the now-defunct Primestar satellite TV service. This all changed when the first American DBS provider, DirecTV, was established in 1994, stealing the limelight from FSS satellite technology for DTH programming (due to DirecTV's smaller 18"-diameter dishes and lower cost of equipment). However, FSS satellites on the C and K_u bands still are used by cable & satellite channels such as CNN, The Weather Channel, HBO, Starz, and others, for distribution to cable tv headends (as mentioned earlier), and to the DBS providers themselves such as DirecTV and Dish Network who then re-distribute these channels over their own DBS systems. The fact that these channels still exist on FSS satellites (more so for reception and re-distribution by cable tv and DBS systems, instead of for DTH viewers) makes TVRO systems for DTH viewing a still-viable option for satellite tv, often being a much-cheaper alternative to DBS, as far as monthly subscription fees are concerned. TVRO-oriented programming packages sold by companies such as National Programming Services[http://www.callnps.com], Bigdish.com[http://www.bigdish.com], and Skyvision[http://www.skyvision.com], are often quite a bit cheaper than their DBS equivalents. Motorola still makes digital 4DTV receivers for DTH TVRO use, and analog TVRO receivers are still available. However, the hardware for a brand-new TVRO system (dish & receiver, along with a VideoCipher or DigiCipher descrambler, or an integrated receiver/decoder (IRD) like a 4DTV system, instead of a separate receiver & descrambler/decoder) nowadays costs quite a bit more than a DBS system (about $1500-2000 USD, including installation). But most older used TVRO systems can be had almost for free, due to most people converting over to DBS systems over the years. Unlike DBS, big-dish TVRO satellite TV also provides a plethora of unscrambled & unencrypted channels such as Classic Arts Showcase, and feeds of syndicated TV shows for reception by local TV stations. Free-to-air satellite TV channels are also usually distributed on FSS satellites in the K_u band. The Intelsat America 5, Galaxy 10R and AMC 3 satellites over North America provide a quite large amount of FTA channels on their K_u-band transponders. Satellites for communication have now been launched that have transponders in the K_a band, such as DirecTV's SPACEWAY-1 satellite. NASA as well has launched experimental satellites utilizing the K_a band recently. See broadcast satellites for further information on FSS and DBS satellites in orbit.

Mobile satellite technologies

Initially available for broadcast to stationary TV receivers, by 2004 popular mobile direct broadcast applications made their appearance with that arrival of two satellite radio systems in the United States: Sirius and XM Satellite Radio Holdings. Some manufacturers have also introduced special antennas for mobile reception of DBS television. Using GPS technology as a reference, these antennas automatically re-aim to the satellite no matter where or how the vehicle (that the antenna is mounted on) is situated. These mobile satellite antennas are popular with some recreational vehicle owners. Such mobile DBS antennas are also used by JetBlue Airways for DirecTV (supplied by LiveTV, a subsidary of JetBlue), which passengers can view on-board on LCD screens mounted in the seats.

Amateur radio

Amateur radio operators have access to the OSCAR satellites that have been designed specifically to carry amateur radio traffic. Most such satellites operate as spaceborne repeaters, and are generally accessed by amateurs equipped with UHF or VHF radio equipment and highly directional antennas such as Yagis or dish antennas. Due to the limitations of ground-based amateur equipment, most amateur satellites are launched into fairly low Earth orbits, and are designed to deal with only a limited number of brief contacts at any given time. Some satellites also provide data-forwarding services using the AX.25 or similar protocols.

Satellite Broadband

In recent years, satellite communication technology has been used as a means to connect to the internet via broadband data connections. This is can be very useful for users to test who are located in very remote areas, and can't access a wireline broadband or dialup connection.

External links

- [http://www.lyngsat.com LyngSat, an on-line directory of FSS & DBS communications satellites, and their transponder information]
- [http://news.bbc.co.uk/2/hi/science/nature/3721312.stm The future of communication satellite business]
- [http://www.hq.nasa.gov/office/pao/History/satcomhistory.html Communications satellites short history] by David J. Whalen
- [http://history.nasa.gov/SP-4217/sp4217.htm Beyond The Ionosphere: Fifty Years of Satellite Communication (NASA SP-4217, 1997)] – an entire book online—scroll down for “contents” link.
- [http://roland.lerc.nasa.gov/~dglover/sat/satcom2.html NASA experimental communications satellites]
- [http://nssdc.gsfc.nasa.gov/nmc/tmp/1963-031A.html Syncom 2 satellite description]
- [http://english.thuraya.pl/linkstar.html VSAT antennas]
- [http://www.lamit.ro Communications trough satellite]
- [http://www.ee.surrey.ac.uk/Personal/L.Wood/constellations/index.html Lloyd’s Satellite Constellations]
- [http://www.satelliteradio.com/ Satellite Radio]
- [http://www.topsatelliteradio.com/what-is-satellite-radio-article.html How Does Satellite Radio Work?]
- [http://www.satcom.co.uk/ Satcom Online – A Resource for Satcom Engineers]
- [http://www.satellitespectrum.com/ Satellite Communication News] Category:Telecommunications equipment Category:Communications satellites ja:通信衛星

Telecommunications

Telecommunication refers to communication over long distances. In practice, something of the message may be lost in the process. Telecommunication covers all forms of distance and/or conversion of the original communications, including radio, telegraphy, television, telephony, data communication and computer networking. The elements of a telecommunication system are a transmitter, a medium (line) and possibly a channel imposed upon the medium (see baseband and broadband as well as multiplexing), and a receiver. The transmitter is a device that transforms or encodes the message into a physical phenomenon; the signal. The transmission medium, by its physical nature, is likely to modify or degrade the signal on its path from the transmitter to the receiver. The receiver has a decoding mechanism capable of recovering the message within certain limits of signal degradation. Sometimes, the final "receiver" is the human eye and/or ear (or in some extreme cases other sensory organs) and the recovery of the message is done by the brain (see psychoacoustics.) Telecommunication can be point-to-point, point-to-multipoint or broadcasting, which is a particular form of point-to-multipoint that goes only from the transmitter to the receivers. One of the roles of the telecommunications engineer is to analyse the physical properties of the line or transmission medium, and the statistical properties of the message in order to design the most effective encoding and decoding mechanisms. When systems are designed to communicate through human sensory organs (mainly those for vision and hearing), physiological and psychological characteristics of human perception must be taken into account. This has important economic implications and engineers must research what defects can be tolerated in the signal and not significantly degrade the viewing or hearing experience.

Examples of human (tele)communications

In a simplistic example, consider a normal conversation between two people. The message is the sentence that the speaker decides to communicate to the listener. The transmitter is the language areas in the brain, the motor cortex, the vocal cords, the larynx, and the mouth that produce those sounds called speech. The signal is the sound waves (pressure fluctuations in air particles) that can be identified as speech. The channel is the air carrying those sound waves, and all the acoustic properties of the surrounding space: echoes, ambient noise, reverberation. Between the speaker and the listener, there might be other devices that do or do not introduce their own distortions of the original vocal signal (for example a telephone, a HAM radio, an IP phone, etc.) The receiver is the listener's ear and auditory system, the auditory nerve, and the language areas in the listener's brain that will "decode" the signal into meaningful information and filter out background noise. All channels have noise. Another important aspect of the channel is called the bandwidth. A low bandwidth channel, such as a telephone, cannot carry all of the audio information that is transmitted in normal conversation, causing distortion and irregularities in the speaker's voice, as compared to normal, in-person speech.

External links

- [http://web.archive.org/web/20040413074912/www.ericsson.com/support/telecom/index.shtml Ericsson's Understanding Telecommunications] at archive.org (Ericsson removed the book from their site in Sep 2005)
- [http://www.carrieraccessbilling.com/telecommunications-glossary-a.asp Intec Telecom Systems' Telecom Dictionary]
- [http://www.mobile-phone-directory.org/Glossary/ Mobile Phone Directory Telecommunications Glossary]
- [http://www.tiaonline.org Telecommunications Industry Association (TIA)]
- [http://www.aronsson.se/hist.html Aronsson's Telecom History Timeline]
- [http://www.alcatel.com/atr Alcatel Telecommunications Review] Telecom magazine published since 1922
- [http://www.teleclick.ca Telecommunications Industry News]
- [http://www.bt.com BT] British Telecommunications company
- Category:Digital Revolution ms:Telekomunikasi ja:電気通信 th:โทรคมนาคม

Molniya orbit

Molniya orbit is a class of a highly elliptic orbit with inclination of 63.4° and orbital period of about 12 hours for which perturbations in argument of perigee are zero. A satellite placed in this orbit spends most of its time over a designated area of the earth, a phenomenon known as apogee dwell. Molniya orbits are named after a series of Soviet/Russian Molniya communications satellites that have been using this class of orbits since the mid 1960s. Molniya orbits are not limited to Earth orbits only as they can be computed for any celestial body for which secular variations in longitude of the ascending node and argument of perigee because of central body’s oblateness have dominant effects on bodies orbiting it.

Properties

For a stationary apogee in either hemisphere, the inclination must be 63.4°. The argument of perigee then remains relatively unchanged, and is set at either 90° or 270°, which locates apogee in the southern or northern hemisphere, respectively.

Use in communications

The Molniya orbit allows for 24h communicatons coverage of polar periods by a constellation of 3 satellites. The first satellite to use this orbit was [http://www.astronautix.com/craft/molniya1.htm Molniya 1-01] launched on August 23, 1965. American satellites have also used Molniya orbits, including the Satellite Data System cluster.

Other uses

Molniya orbit is not suitable for manned spacecraft as it crosses high-energy Van Allen belt. According to some sources, the Soviet Fractional Orbital Bombardment System functioned by mimicking a standard satellite travelling in a Molniya orbit.

Derivation

In order to achieve that position of the apogee is not severely affected by orbit perturbations, an inclination close to 63.4° degrees is chosen. This results in the argument of perigee remaining nearly constant for a long period of time. The formula for the argument of perigee change per day is as follows: :

\Delta \omega_  = 4.98^\circ \left(  \right)^ \frac

The equation becomes zero for an inclination of 63.4 degrees.

References

- [http://www.braeunig.us/space/orbmech.htm Orbital Mechanics] by Robert A. Braeunig
- [http://www.astronautix.com/craft/molniya1.htm Molniya-1 spacecraft] by Mark Wade of [http://www.astronautix.com Encyclopedia Astronautica]

Fiber optic

An optical fiber (also spelled fibre) is a transparent thin fiber, usually made of glass or plastic, for transmitting light. Fiber optics is the branch of science and engineering concerned with such optical fibers.

Optical description

Optical fiber is a cylindrical structure that transmits light along its axis. The fiber consists of a core surrounded by a cladding layer. Like other glasses, the glass used in optical fiber has a refractive index of about 1.5. For the fiber to guide the optical signal the refractive index of the core must be slightly higher than that of the cladding, though typically the difference is less than one per cent. The boundary between the core and cladding may either be abrupt, in step-index fiber, or gradual, in graded-index fiber. graded-index fiber Fiber with large core diameter, called multi-mode fiber (from the electromagnetic analysis, see below), may be analyzed by geometric optics. In a step-index fiber, rays of light are guided along the fiber core by total internal reflection. Rays that meet the core-cladding boundary at a high angle (measured relative to a line normal to the boundary) are completely reflected. The minimum angle for total internal reflection is determined by the difference in index of refraction between the core and cladding materials. Rays that meet the boundary at a low angle are refracted from the core into the cladding, where they are not useful for conveying light along the fiber. In this way, the minimum angle for total internal reflection determines the acceptance angle of the fiber, often reported as a numerical aperture. A high numerical aperture makes it easier to efficiently couple a transmitter or receiver to the fiber. However, by allowing light to propagate down the fiber in rays both close to the axis and at various angles, a high numerical aperture also increases the amount of multi-path spreading, or dispersion, that affects light pulses in the fiber. In graded-index fiber, the index of refraction in the core decreases continuously between the axis and the cladding. This reduces multi-path dispersion because the high angle rays pass more through the lower-index periphery of the core, rather than the high-index center. Index grading also causes light rays to bend smoothly as they approach the cladding, rather than reflect abruptly from the core-cladding boundary. The index profile is chosen to minimize the difference in axial propagation speeds of the various rays in the fiber. This ideal index profile is very close to a parabolic relationship between the index and the distance from the axis. Fiber with a core diameter narrower than a few wavelengths of the light carried, is analyzed as an electromagnetic structure. The electromagnetic analysis may also be required to understand behaviors such as speckle that occur when coherent light propagates in multi-mode fiber. The optical fiber is seen as a cylindrical dielectric wave guide. This wave guide supports one or more confined transverse modes by which light can propagate along its axis. Fiber supporting only one mode is called single-mode or mono-mode fiber, while fiber that supports more than one mode is called multi-mode fiber. By the waveguide analysis, it is seen that the light energy in the fiber is not completely confined in the core, but, especially in single-mode fibers, a significant fraction of the energy in the bound mode travels in the cladding as an evanescent wave. bound mode The common type of single-mode fiber, as described in Federal Standard 1037C, has a core diameter of 8 to 10 micrometres. It is notable that the mode structure depends on the wavelength of the light used, so that this fiber actually supports a small number of additional modes at visible wavelengths. Multi-mode fiber, by comparison, is manufactured with a core diameter of 50 µm, 62.5 µm, or larger. Some special-purpose optical fiber is constructed with a non-cylindrical core and/or cladding layer, usually with an elliptical or rectangular cross-section. These include polarization-maintaining fiber and fiber designed to suppress whispering gallery mode propagation. Glass optical fibers are almost always made from silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses are used for longer-wavelength infrared applications. At high optical powers, above one watt, when a fiber is subjected to a shock or is otherwise suddenly damaged, a fiber fuse can occur. The reflection from the damage vaporizes the fiber immediately before the break, and this new defect remains reflective so that the damage propagates back toward the transmitter at 1–3 meters per second ^,^,. The open fiber control system, which ensures laser eye safety in the event of a broken fiber, can also effectively halt propogation of the fiber fuse . In situations, such as undersea cables, where high power levels might be used without the need for open fiber control, a "Fiber fuse" protection device at the transmitter can break the circuit to prevent damage.

Optical fiber communication

The optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables. Although fibers can be made out of either transparent plastic or glass, the fibers used in long-distance telecommunications applications are always glass, because of the lower optical attenuation. Both multi-mode and single-mode fibers are used in communications, with multi-mode fiber used mostly for short distances (up to 500 m), and single-mode fiber used for longer distance links. Because of the tighter tolerances required to couple light into and between single-mode fibers, single-mode transmitters, receivers, amplifiers and other components are generally more expensive than multi-mode components. The light used is typically infrared light, at wavelengths near to the minimum absorption wavelength of the fiber in use. The fiber absorption is minimal for 1550 nm light and dispersion is minimal at 1310 nm making these the optimal wavelength regions for data transmission. A local minimum of absorption is found near 850 nm, a wavelength for which low cost transmitters and receivers can be designed, and this wavelength is often used for short distance applications. Fibers are generally used in pairs, with one fiber of the pair carrying a signal in each direction. For modern glass optical fiber, the maximum transmission distance is limited not by attenuation but by dispersion, or spreading of optical pulses as they travel along the fiber. Dispersion in optical fibers is caused by a variety of factors. Intermodal dispersion, caused by the different axial speeds of different transverse modes, limits the performance of multi-mode fiber. Because single-mode fiber supports only one transverse mode, intermodal dispersion is eliminated. For single-mode fiber performance is limited by chromatic dispersion, which occurs because the index of the glass varies slightly depending on the wavelength of the light, and light from real optical transmitters has nonzero spectral width. Polarization mode dispersion, which can limit the performance of single-mode systems, occurs because although the single-mode fiber can sustain only one transverse mode, it can carry this mode with two different polarizations, and slight imperfections or distortions in a fiber can alter the propagation velocities for the two polarizations. Dispersion limits the bandwidth of the fiber because the spreading optical pulse limits the rate that pulses can follow one another on the fiber and still be distinguishable at the receiver. Because the effect of dispersion increases with the length of the fiber, a fiber transmission system is often characterized by its bandwidth-distance product, often expressed in units of MHz×km. This value is a product of bandwidth and distance because there is a tradeoff between the bandwidth of the signal and the distance it can be carried. For example, a common multimode fiber with bandwidth-distance product of 500 MHz×km could carry a 500 MHz signal for 1 km or a 1000 MHz signal for 0.5 km. In single-mode fiber systems, both the fiber characteristics and the spectral width of the transmitter contribute to determining the bandwidth-distance product of the system. Typical single-mode systems can sustain transmission distances of 80 to 140 km (50 to 87 miles) between regenerations of the signal. By using an extremely narrow-spectrum laser source, data rates of up to 40 gigabits per second are achieved in real-world applications. Using Wavelength division multiplexing (WDM), the bandwidth carried by a single fiber can be increased into the range of terabits per second. This is accomplished by transmitting many wavelengths at once on the fiber. Wavelength division multiplexers and demultiplexers are used to combine and split up the wavelengths at each end of the link. In coarse WDM (CWDM) only a few wavelengths are used. One use of CWDM is to allow bidirectional communications over one fiber. Recent advances in fiber technology have reduced losses so far that no amplification of the optical signal is needed over distances of hundreds of kilometers. This has greatly reduced the cost of optical networking, particularly over undersea spans where the cost reliability of amplifiers is one of the key factors determining the performance of the whole cable system. In the past few years several manufacturers of submarine cable line terminal equipment have introduced upgrades that promise to quadruple the capacity of older submarine systems installed in the early to mid-1990s. These advances have been the result of increased investigation into two different fields. One is dispersion management, which seeks to balance the effects of dispersion against nonlinearity. The other is solitons. The range of long-range systems is extended by the use of optical amplifiers, typically made by doping a length of fiber with the rare-earth mineral erbium, and pumping it with light from a laser with a shorter wavelength than the communications signal.

Comparison with electrical transmission

The choice between optical fiber and electrical (or "copper") transmission for a particular system is made based on a number of trade-offs. Optical fiber is generally chosen for systems with higher bandwidths, spanning longer distances, than electrical cabling can provide. The main benefits of fiber are its exceptionally low loss, allowing long distances between amplifiers or repeaters; and its inherently high data-carrying capacity, such that thousands of electrical links would be required to replace a single high bandwidth fiber. One further benefit of fiber is that even when run alongside each other for long distances, fiber cables experience effectively no crosstalk, in contrast to some types of electrical transmission lines. In short distance and relatively low bandwidth applications, electrical transmission is often preferred because of its
- Lower material cost, when cabling is not required.
- Lower cost of transmitters and receivers.
- Ease of splicing.
- Capability to carry electrical power as well as signals. Because of these benefits of electrical transmission, optical communication is not common in short box-to-box, backplane, or chip-to-chip applications; however, optical systems on those scales have been demonstrated in the laboratory. In certain situations fiber may be used even for short distance or low bandwidth applications, due to other important features:
- Immunity to electromagnetic interference, including nuclear electromagnetic pulses (although fiber can be damaged by alpha and beta radiation).
- High electrical resistance, making it safe to use near high-voltage equipment or between areas with different earth potentials.
- Low weight, important in aircraft.
- No sparks, important in flammable or explosive gas environments.
- Not electromagnetically radiating, and difficult to tap without disrupting the signal, important in high-security environments.

Other uses of optical fibers

- Fibers can be used as light guides in medical and other applications where bright light needs to be brought to bear on a target without a clear line-of-sight path.
- Lasers and optical amplifiers can use doped optical fiber as a gain medium.
- Optical fibers can be used as sensors to measure strain, temperature, pressure and other parameters.
- Bundles of fibers are used along with lenses for long, thin imaging devices called endoscopes, which are used to view objects through a small hole. Medical endoscopes are used for minimally invasive exploratory or surgical procedures (endoscopy). Industrial endoscopes (see fiberscope or borescope) are used for inspecting anything hard to reach, such as jet engine interiors.
- In some high-tech buildings, optical fibers are used to route sunlight from the roof to other parts of the building (see non-imaging optics).
- Optical fibers have many decorative applications, including signs and art, artificial Christmas trees, and lighting.
- The German company Sennheiser developed a microphone working with a laser and optical fibers.

Manufacture

Optical fiber is made by first constructing a large-diameter preform, with a carefully controlled refractive index profile, and then pulling the preform to form the long, thin optical fiber. The preform is commonly made by three chemical vapor deposition methods: inside vapor deposition, outside vapor deposition, and vapor axial deposition. In inside vapor deposition, a hollow glass tube approximately 40 cm in length known as a "preform" is placed horizontally and rotated slowly on a lathe, and gases such as silicon tetrachloride (SiCl₄) or germanium tetrachloride (GeCl₄) are injected with oxygen in the end of the tube. The gases are then heated by means of an external hydrogen burner, bringing the temperature of the gas up to 1900 kelvin, where the tetrachlorides react with oxygen to produce silica or germania (germanium oxide) particles. When the reaction conditions are chosen to allow this reaction to occur in the gas phase throughout the tube volume, in contrast to earlier techniques where the reaction occurred only on the glass surface, this technique is called modified chemical vapor deposition. The oxide particles then agglomerate to form large particle chains, which subsequently deposit on the walls of the tube as soot. The deposition is due to the large difference in temperature between the gas core and the wall causing the gas to push the particles outwards (this is known as thermophoresis). The torch is then traversed up and down the length of the tube to deposit the material evenly. After the torch has reached the end of the tube, it is then brought back to the beginning of the tube and the deposited particles are then melted to form a solid layer. This process is repeated until a sufficient amount of material has been deposited. For each layer the composition can be varied by varying the gas composition, resulting in precise control of the finished fiber's optical properties. In outside vapor deposition or vapor axial deposition, the glass is formed by flame hydrolysis, a reaction in which silicon tetrachloride and germanium tetrachloride are oxidized by reaction with water (H₂O) in an oxyhydrogen flame. In outside vapor deposition the glass is deposited onto a solid rod, which is removed before further processing. In vapor axial deposition, a short seed rod is used, and a porous preform, whose length is not limitted by the size of the source rod, is built up on its end. The porous preform is consolidated into a transparent, solid perform by heating to about 1800 kelvin. The preform, however constructed, is then placed in a device known as a drawing tower, where the perform tip is heated and the optic fiber is pulled out as a string. By measuring the resultant fiber width, the tension on the fiber can be controlled to maintain the fiber thickness.

Optical fiber cables

In practical fibers, the cladding is usually coated with a tough resin buffer layer, which may be further surrounded by a jacket layer, usually plastic. These layers add strength to the fiber but do not contribute to its optical wave guide properties. For indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer (e.g. Kevlar) strength members, in a lightweight plastic cover to form a simple cable. Each end of the cable may be terminated with a specialized optical fiber connector to allow it to be easily connected and disconnected from transmitting and receiving equipment. For use in more strenuous environments, a much more robust cable construction is required. In loose-tube construction the fiber is laid helically into semi-rigid tubes, allowing the cable to stretch without stretching the fiber itself. This protects the fiber from tension during laying and due to temperature changes. Alternatively the fiber may be embedded in a heavy polymer jacket. These fiber units are commonly attached to additional steel strength members, again with a helical twist to allow for stretching. Another critical concern in cabling is to protect the fiber from contamination by water, because its component hydrogen and hydroxyl ions can diffuse into the fiber, reducing the fiber's strength and increasing the optical attenuation. Water is kept out of the cable by use of solid barriers such as copper tubes, or water-repellant jelly surrounding the fiber. Finally, the cable may be armored to protect it from environmental hazards, such as construction work or gnawing animals. Undersea cables are more heavily armored in their near-shore portions to protect them from boat anchors, fishing gear, and even sharks, which may be attracted to the electrical power signals that are carried to power amplifiers or repeaters in the cable. Modern fiber cables can contain up to a thousand fibers in a single cable, so the performance of optical networks easily accommodate even today's demands for bandwidth on a point-to-point basis. However, unused point-to-point potential bandwidth does not translate to operating profits, and it is estimated that no more than 1% of the optical fiber buried in recent years is actually 'lit'. Modern cables come in a wide variety of sheathings and armor, designed for applications such as direct burial in trenches, installation in conduit, lashing to aerial telephone poles, submarine installation, or insertion in paved streets. In recent years the cost of small fiber-count pole mounted cables has greatly decreased due to the high Japanese and South Korean demand for Fiber to the Home (FTTH) installations.

History

The history of dielectric optical lightguides goes back to Victorian times, when the total internal reflection principle was used to illuminate streams of water in elaborate public fountains. Later development, in the early-to-mid twentieth century, focussed on the development of fiber bundles for image transmission, with the primary application being the medical gastroscope. The first fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, and Lawrence E. Curtiss in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material. A variety of other image transmission applications soon followed. Basil Hirschowitz In 1965, Charles K. Kao and George A. Hockham of the British Post Office were the first to recognize that attenuation of contemporary fibers was caused by impurities, which could be removed, rather than fundamental physical effects such as scattering. They demonstrated that optical fiber could be a practical medium for communication, if the attenuation could be reduced below 20 dB per kilometer (Hecht, 1999, p. 114). By this measure, the first practical optical fiber for communications was invented in 1970 by researchers Robert D. Maurer, Donald Keck, Peter Schultz, and Frank Zimar working for American glass maker Corning Glass Works. They manufactured a fiber with 17 dB optic attenuation per kilometer by doping silica glass with titanium. The erbium-doped fiber amplifier, which reduced the cost of long-distance fiber systems by eliminating the need for optical-electrical-optical repeaters, was invented by David Payne of the University of Southampton, in 1987. The first transatlantic telephone cable to use optical fiber was TAT-8, which went into operation in 1988. In the late 1990s through 2000, the fiber optics industry became associated with the dot-com stock-market bubble. Industry promoters predicted vast increases in demand for communications bandwidth due to increased use of the Internet, and commercialization of various bandwidth-intensive consumer services, such as video on demand. Internet protocol data traffic was said to be increasing exponentially, and at a faster rate than integrated circuit complexity had increased under Moore's Law. Since the bust of the dot-com bubble, however, the main trend in the industry has been consolidation of firms and offshoring of manufacturing to reduce costs.

References

- Gambling, W. A., "The Rise and Rise of Optical Fibers", IEEE Journal on Selected Topics in Quantum Electronics, Vol. 6, No. 6, pp. 1084-1093, Nov./Dec. 2000
- Gowar, John, Optical Communication Systems, 2 ed., Prentice-Hall, Hempstead UK, 1993 (ISBN 0136387276)
- Hecht, Jeff, City of Light, The Story of Fiber Optics, Oxford University Press, New York, 1999 (ISBN 0195108183)
- Nagel S. R., MacChesney J. B., Walker K. L., "An Overview of the Modified Chemical Vapor Deposition (MCVD) Process and Performance", IEEE Journal of Quantum Mechanics, Vol. QE-18, No. 4, April 1982 # # # # #

External links

- [http://www.siemon.com/us/standards/13-14_optical_fiber_cabling.asp Optical Fiber Cabling Standards]
- [http://www.thefoa.org/ The Fiber Optic Association]
- [http://www.jimhayes.com/lennielw/ Lennie Lightwave's Guide To Fiber Optics] Category:Fiber optics Category:Telecommunications equipment Category:Signal cables ja:光ファイバー

Project SCORE

Project SCORE (Signal Communications Orbit Relay Equipment) was the world’s first communications satellite. Launched in an Atlas rocket on December 18 1958, SCORE provided a first test of a communications relay system in space and captured world attention by broadcasting a Christmas message from President Eisenhower through an onboard tape recorder. SCORE was developed by the U.S. Army Signal Research and Development Laboratory (SRDL) at Fort Monmouth, New Jersey in a six-month effort. The payload used store and forward technology, weighed 68 kg (150 pounds) and was built into the Atlas rocket. SCORE was placed into a 183 km by 1,481 km (114 mile by 920 mile) orbit, inclined 32.3 degrees, with a period of 101.5 minutes. Its batteries lasted 12 days and it reentered the atmosphere on 21 January 1959.

External link

- http://www.globalsecurity.org/space/systems/score.htm Category:Communications satellites

Store and forward

Store and forward is a communications technique in which messages are sent to an intermediate station where they are kept and sent at a later time to the final destination or to another intermediate station. Reasons for using this method include:
- Origin and destination stations may not be available for communications at the same time
- One or more circuits may not have enough capacity for peak traffic and there is a need to give priority to certain messages, without losing the others. This technique is especially used in messaging-based systems such as e-mail, SMS, MMS and so on.

References

- [http://support.intel.com/support/express/switches/sb/cs-014410.htm Switches - What Are Forwarding Modes and How Do They Work?]

NASA

] The National Aeronautics and Space Administration (NASA), which was established in 1958, is the agency responsible for the public space program of the United States of America. It is also responsible for long-term civilian and military aerospace research.

Vision and mission

NASA's vision is "to improve life here, extend life to there, and to find life beyond." Its mission is "to understand and protect our home planet; to explore the Universe and search for life; and to inspire the next generation of explorers."

History

Space Race

:For additional background, please see the Space Race article Space Race launch of Redstone rocket and NASA's Mercury 3 capsule Freedom 7 with Alan Shepard Jr. on the United States' first human flight into sub-orbital space. (Atlas rockets were used to launch Mercury's orbital missions.)]] Following the Soviet space program's launch of the world's first man-made satellite (Sputnik 1) on October 4, 1957, the attention of the United States turned toward its own fledgling space efforts. The U.S. Congress, alarmed by the perceived threat to U.S. security and technological leadership, urged immediate and swift action; President Dwight D. Eisenhower and his advisers counseled more deliberate measures. Several months of debate produced agreement that a new federal agency was needed to conduct all nonmilitary activity in space. On July 29, 1958, President Eisenhower signed the National Aeronautics and Space Act of 1958 establishing the National Aeronautics and Space Administration (NASA). When it began operations on October 1, 1958, NASA consisted mainly of the four laboratories and some 8,000 employees of the government's 46-year-old research agency for aeronautics, the National Advisory Committee for Aeronautics (NACA), though the probably most important contribution actually had its roots in the German rocket program led by Wernher von Braun, who is today regarded as the father of the United States space program. NASA's early programs were research into human spaceflight, and were conducted under the pressure of the competition between the USA and the USSR (the Space Race) that existed during the Cold War. The Mercury program, initiated in 1958, started NASA down the path of human space exploration with missions designed to discover simply if man could survive in space. Representatives from the U.S. Army (M.L. Raines, LTC, USA), Navy (P.L. Havenstein, CDR, USN) and Air Force (K.G. Lindell, COL, USAF) were selected/requested to provide assistance to the NASA Space Task Group through coordination with the existing U.S. military research and defense contracting infrastructure, and technical assistance resulting from experimental aircraft (and the associated military test pilot pool) development in the 1950s. On May 5, 1961, astronaut Alan B. Shepard Jr. became the first American in space when he piloted Freedom 7 on a 15-minute suborbital flight. John Glenn became the first American to orbit the Earth on February 20, 1962 during the 5-hour flight of Friendship 7. Once the Mercury project proved that human spaceflight was possible, project Gemini was launched to conduct experiments and work out issues relating to a moon mission. The first Gemini flight with astronauts on board, Gemini III, was flown by Virgil "Gus" Grissom and John W. Young on March 23, 1965. Nine other missions followed, showing that long-duration human space flight was possible, proving that rendezvous and docking with another vehicle in space was possible, and gathering medical data on the effects of weightlessness on humans.

Apollo program

Following the success of the Mercury and Gemini programs, the Apollo program was launched to try to do interesting work in space and possibly put men around (but not on) the Moon. The direction of the Apollo program was radically altered following President John F. Kennedy's announcement on May 25, 1961 that the United States should commit itself to "landing a man on the Moon and returning him safely to the Earth" by 1970. Thus Apollo became a program to land men on the Moon. The Gemini program was started shortly thereafter to provide an interim spacecraft to prove techniques needed for the now much more complicated Apollo missions. Gemini program.]] After eight years of preliminary missions, including NASA's first loss of astronauts with the Apollo 1 launch pad fire, and the first spacecraft to orbit the Moon (Apollo 8) at the end of 1968, the Apollo program achieved its goals with Apollo 11 which landed Neil Armstrong and Buzz Aldrin on the moon's surface on July 20, 1969 and returned them to Earth safely on July 24. Armstrong's first words upon stepping out of the Eagle lander captured the momentousness of the occasion: "That's one small step for [a] man, one giant leap for mankind." Twelve men would set foot on the Moon by the end of the Apollo program in December 1972. NASA had won the moon race, and in some senses this left it without direction, or at the very least without the public attention and interest that was necessary to guarantee large budgets from Congress. After President Lyndon Johnson left office, NASA lost its main political supporter, and rocket scientist Wernher von Braun was moved to a position lobbying in Washington. Plans for ambitious follow-on projects to construct a space station, establish a lunar base and launch a human mission to Mars by 1990 were proposed but with the end to procurement of Saturn and Apollo hardware, there was no capability to support these. The near-disaster of Apollo 13, where an oxygen tank explosion nearly doomed all three astronauts, helped to recapture national attention and concern. Although missions up to Apollo 20 were planned, Apollo 17 was the last mission to fly under the Apollo banner. The program ended because of budget cuts (in part due to the Vietnam War) and the desire to develop a reusable space vehicle.

Other early missions

Although the vast majority of NASA's budget has been spent on human spaceflight, there have been many robotic missions instigated by the space agency. In 1962 the Mariner 2 mission was launched and became the first spacecraft to make a flyby of another planet – in this case Venus. The Ranger, Surveyor, and Lunar Orbiter missions were essential to assessing lunar conditions before attempting Apollo landings with humans on board. Later, the two Viking probes landed on the surface of Mars and sent color images back to Earth, but perhaps more impressive were the Pioneer and particularly Voyager missions that visited Jupiter, Saturn, Uranus and Neptune sending back scientific information and color images. Having lost the moon race, the Soviet Union had, along with the USA, changed its approach. On July 17, 1975 an Apollo craft (finding a new use after the cancelling of planned lunar flights) was docked to the Soviet Soyuz 19 spacecraft, in the Apollo-Soyuz Test Project. Although the Cold War would last many more years, this was a critical point in NASA's history and much of the international co-operation in space exploration that exists today has its genesis with this mission. America's first space station, Skylab, occupied NASA from the end of Apollo until the late 1970s.

Shuttle era

Skylab 1981 ]] The space shuttle became the major focus of NASA in the late 1970s and the 1980s. Planned to be a frequently launchable and mostly reusable vehicle, four space shuttles were built by 1985. The first to launch, Columbia did so on April 12, 1981. The shuttle was not all good news for NASA – flights were much more expensive than initially projected, and even after the 1986 Challenger disaster highlighted the risks of space flight, the public again lost interest as missions appeared to become mundane. Work began on Space Station Freedom as a focus for the manned space programme but within NASA there was argument that these projects came at the expense of more inspiring unmanned missions such as the Voyager probes. The Challenger disaster aside the late 1980s marked a low point for NASA. Nonetheless, the shuttle has been used to launch milestone projects like the Hubble Space Telescope (HST). The HST was created with a relatively small budget of $2 billion but has continued operation since 1990 and has delighted both scientists and the public. Some of the images it has returned have become near-legendary, such as the groundbreaking Hubble Deep Field images. The HST is a joint project between ESA and NASA, and its success has paved the way for greater collaboration between the agencies. In 1995 Russian-American interaction would again be achieved as the Shuttle-Mir missions began, and once more a Russian craft (this time a full-fledged space station) docked with an American vehicle. This cooperation continues to the present day, with Russia and America the two biggest partners in the largest space station ever built – the International Space Station (ISS). The strength of their cooperation on this project was even more evident when NASA began relying on Russian launch vehicles to service the ISS following the 2003 Columbia disaster, which grounded the shuttle fleet for well over two years. Costing over one hundred billion dollars, it has been difficult at times for NASA to justify the ISS. The population at large have historically been hard to impress with details of scientific experiments in space, preferring news of grand projects to exotic locations. Even now, the ISS cannot accommodate as many scientists as planned. During much of the 1990s, NASA was faced with shrinking annual budgets due to Congressional belt-tightening in Washington, DC. In response, NASA's ninth administrator, Daniel S. Goldin, pioneered the "faster, better, cheaper" approach that enabled NASA to cut costs while still delivering a wide variety of aerospace programs (Discovery Program). That method was criticized and re-evaluated following the twin losses of Mars Climate Orbiter and Mars Polar Lander in 1999.

NASA's future

Mars Polar Lander and the planned crew and heavy lift launch vehicles]] NASA's most publicly-inspiring mission of recent years has probably been the Mars Pathfinder mission of 1997. Newspapers around the world carried images of the lander dispatching its own rover, Sojourner, to explore the surface of Mars in a way never done before at any extra-terrestrial location. Less publicly acclaimed but performing science from 1997 to date (2005) has been the Mars Global Surveyor orbiter. Since 2001, the orbiting Mars Odyssey has been searching for evidence of past or present water and volcanic activity on the red planet. NASA expects to continue exploring the Red Planet with more spacecraft such as the Mars Reconnaissance Orbiter, which will reach Mars in 2006. The Space Shuttle Columbia disaster in 2003, which killed the crew of six American and one Israeli astronaut, and caused a 29-month hiatus in space shuttle flights, triggered a serious re-examination of NASA's priorities. The U.S. government, various scientists, and the public all considered the future of the space program. On January 14, 2004, ten days after the landing of Mars Exploration Rover Spirit, President George W. Bush announced a new plan for NASA's future, dubbed the Vision for Space Exploration. According to this plan, humankind will return to the moon by 2020, and set up outposts as a testbed and potential resource for future missions. The space shuttle will be retired in 2010 and the Crew Exploration Vehicle will replace it by 2014, capable of both docking with the ISS and leaving the Earth's orbit. The future of the ISS is somewhat uncertain – construction will be completed, but beyond that is less clear. Although the plan initially met with skepticism from Congress, in late 2004 Congress agreed to provide start-up funds for the first year's worth of the new space vision. Hoping to spur innovation from the private sector, NASA established a series of Centennial Challenges, technology prizes for non-government teams, in 2004. The Challenges include tasks that will be useful for implementing the Vision for Space Exploration, such as building more efficient astronaut gloves.

Criticisms

Some commentators, such as Mark Wade, note that NASA has suffered from a 'stop-start' approach to its human spaceflight programs. The Apollo spacecraft and Saturn family of launch vehicles were abandoned in 1970 after billions of dollars had been spent on their development. In 2004 the U.S. Government proposed eventually replacing the Shuttle with a Crew Exploration Vehicle that would allow the agency to again send astronauts to the Moon. Despite the reduction of its budget following project Apollo, NASA has maintained a top-heavy bureaucracy resulting in inflated costs and compromised hardware. Crew Exploration Vehicle on October 31, 1998.]] Currently, the ISS relies on the Shuttle fleet for all major construction shipments. The Shuttle fleet has lost two spacecraft and fourteen astronauts in two disasters in 1986 and 2003. While the 1986 loss was made up with a Shuttle built from replacement parts, NASA does not plan to build another shuttle to replace the second loss. (But see also CEV.) The ISS, which was intended to have a crew of seven as of 2005, now has a skeleton crew of two, causing many intended research projects to be delayed. Other nations that have invested heavily in the space station's construction, such as the members of the European Space Agency, are fearful that the ISS's fate will soon match the fate of Skylab. As of 2005, however, all of the European and Japanese contributions to the ISS are years behind development schedule themselves.

NASA spaceflight missions

Human spaceflight

- Mercury program
- Gemini program
- Apollo program
- Skylab
- Space Shuttle
- International Space Station (working together with ESA, Rosviakosmos and JAXA)
- Project Constellation

Robotic space missions

- Earth Observing
- Upper Atmosphere Research Satellite
- TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics)
- Lunar missions
- Ranger
- Surveyor
- Lunar Orbiter
- Clementine
- Lunar Prospector
- Mercury missions
- Mariner 10
- MESSENGER
- Venus missions
- Mariner 2, 5 and 10
- Pioneer Venus
- Magellan
- Mars missions
- Mariner 4, 6, 7, 8 and 9
- Viking 1 and 2
- Mars Observer
- Mars Pathfinder
- Mars Climate Orbiter
- Mars Polar Lander
- Mars Global Surveyor
- 2001 Mars Odyssey
- Mars Exploration Rovers
- Mars Reconnaissance Orbiter
- Phoenix Lander (Planned for 2007)
- Mars Science Laboratory (Planned for 2009)
- Jupiter missions
- Pioneer 10
- Galileo
- Juno
- Saturn missions
- Cassini-Huygens together with ESA
- Multi-planet missions
- Pioneer 11 – Jupiter and Saturn
- Mariner 10 – Venus and Mercury
- Voyager 1 – Jupiter and Saturn
- Voyager 2 – Jupiter, Saturn, Uranus and Neptune
- New Horizons (Planned for 2006) – Jupiter, Pluto and Kuiper Belt
- Asteroidal/cometary missions
- NEAR Shoemaker
- Deep Space 1
- Stardust
- Deep Impact
- Dawn (Planned for 2006)
- Proposed or canceled planetary-asteroid missions
- JIMO (cancelled)
- CRAF (cancelled)
- NetLanders (cancelled)
- Pluto Kuiper Express (cancelled; New Horizons is replacement)
- Titan Explorer (proposed)
- Neptune Orbiter (proposed)
- Sun observing missions
- SOHO – ESA partnership
- Ulysses – ESA partnership
- Great Observatories for Space Astrophysics
- Hubble Space Telescope – ESA partnership
- Compton Gamma Ray Observatory
- Chandra X-ray Observatory
- Spitzer Space Telescope (formerly known as the Space Infrared Telescope Facility, SIRTF)
- Other observatories
- COBE
- FUSE
- Infrared Astronomical Satellite
- James Webb Space Telescope – ESA partnership
- WMAP

List of NASA administrators

# T. Keith Glennan (1958–1961) # James E. Webb (1961–1968) # Thomas O. Paine (1969–1970) # James C. Fletcher (1971–1977) # Robert A. Frosch (1977–1981) # James M. Beggs (1981–1985) # James C. Fletcher (1986–1989) # Richard H. Truly (1989–1992) # Daniel S. Goldin (1992–2001) # Sean O'Keefe (2001–2005) # Michael Griffin (2005–)

Field installations

In addition to headquarters in Washington, D.C., NASA has field installations at:
- Ames Research Center, Moffett Field, California
- Dryden Flight Research Center, Edwards, California
- John H. Glenn Research Center at Lewis Field, Cleveland, Ohio
- Goddard Space Flight Center, Greenbelt, Maryland
- Goddard Institute for Space Studies, New York, New York
- Independent Verification and Validation Facility, Fairmont, West Virginia
- Wallops Flight Facility, Wallops Island, Virginia
- Jet Propulsion Laboratory, near Pasadena, California
- Deep Space Network stations:
- Goldstone Deep Space Communications Complex, Barstow, California
- Madrid Deep Space Communication Complex, Madrid, Spain
- Canberra Deep Space Communications Complex, Canberra, Australian Capital Territory
- Lyndon B. Johnson Space Center, Houston, Texas
- White Sands Test Facility, Las Cruces, New Mexico
- John F. Kennedy Space Center, Florida
- Langley Research Center, Hampton, Virginia
- George C. Marshall Space Flight Center, Huntsville, Alabama
- Michoud Assembly Facility, New Orleans, Louisiana
- John C. Stennis Space Center, Bay St. Louis, Mississippi

Awards and decorations

NASA presently bestows a number of medals and decorations to astronauts and other NASA personnel. Some awards are authorized for wear on active duty military uniforms. Current NASA awards are as follows:
- Congressional Space Medal of Honor
- NASA Distinguished Public Service Medal
- NASA Distinguished Service Medal
- NASA Equal Employment Opportunity Medal
- NASA Exceptional Achievement Medal
- NASA Exceptional Administrative Achievement Medal
- NASA Exceptional Bravery Medal
- NASA Exceptional Engineering Achievement Medal
- NASA Exceptional Scientific Achievement Medal
- NASA Exceptional Service Medal
- NASA Exceptional Technological Achievement Medal
- NASA Outstanding Leadership Medal
- NASA Public Service Medal
- NASA Space Flight Medal

Related legislation

- 1958 – National Aeronautics and Space Administration PL 85-568 (passed on July 29)
- 1961 – Apollo mission funding PL 87-98 A
- 1970 – National Aeronautics and Space Administration Research and Development Act PL 91-119
- 1984 – National Aeronautics and Space Administration Authorization Act PL 98-361
- 1988 – National Aeronautics and Space Administration Authorization Act PL 100-685
- NASA Budget 1958–2005 in 1996 Constant Year Dollars

External links

General

- [http://www.nasa.gov NASA Home Page]
- [http://www.nasawatch.com NASA Watch]
-

Further research

- [http://history.nasa.gov/series95.html NASA History Series Publications]
- [http://history.nasa.gov/SP-4012/cover.html NASA Historical Data Books (SP-4012)]
- [http://www.hq.nasa.gov/office/pao/History/hhrhist.pdf Research in NASA History: A Guide to the NASA History Program (large PDF – over 1,012 kb)]
- [http://ntrs.nasa.gov/ NTRS: NASA Technical Reports Server]
- [http://www.eventscope.org Eventscope] Category:Independent Agencies of the United States Government ko:미국항공우주국 ja:アメリカ航空宇宙局 simple:NASA th:องค์การนาซา

Echo satellite

The Echo satellites were NASA's first communications satellite experiment. Each spacecraft was designed as a metallized balloon satellite acting as a passive reflector of microwave signals. Communication signals were bounced off of it from one point on Earth to another.

Echo 1

Following the failure of the Delta rocket carrying Echo 1 on May 13, 1960, Echo 1A (commonly referred to as just Echo 1) was successfully put in a 1519 x 1687 km orbit on August 12, 1960. The 30.5 meter (100 foot) diameter balloon was made of 0.127 mm (0.005 inch) thick Mylar polyester film and was successfully used to redirect transcontinental and intercontinental telephone, radio, and television signals. The satellite also aided the calculation of atmospheric density and solar pressure due to its large area-to-mass ratio. As its shiny surface was also reflective in the range of visible light, Echo 1A was visible to the unaided eye over most of the Earth. Brighter than most stars, it was probably seen by more people than any other man-made object in space. Echo 1A reentered Earth's atmosphere and burned up on May 24, 1968.

Echo 2

Echo 2, a 41.1 m diameter Mylar balloon with an improved inflation system to improve the balloon's smoothness and sphericity, was launched January 25, 1964 on a Thor Agena rocket. It was used for more passive communications experiments, and also to investigate the dynamics of large spacecraft and for global geometric geodesy. NASA abandoned passive communications systems in favor of active satellites following Echo 2. Echo 2 reentered on June 7, 1969. ---- Military use: Gray (1992) reports that the Echo satellite program also provided the astronomical reference points required to accurately locate the Russian city of Moscow geographically. This improved accuracy was sought by the US Military for the purpose of targeting intercontinental ballistic missiles. Gray, M. (1992) Angle of Attack: Harrison Storms and the Race to the Moon. pp 5-6, Pub: W. W. Norton & Co Inc. ISBN: 039301892X.

Source

- [http://samadhi.jpl.nasa.gov/msl/QuickLooks/echoQL.html JPL The Mission and Spacecraft Library] Category:Communications satellites

1960

1960 (MCMLX) was a leap year starting on Friday (link will take you to calendar).

Events

January-February

- January - State of emergency is lifted in Kenya - Mau Mau Rebellion is officially over
- January 1 - Independence of Cameroon
- January 9-11 - Aswan High Dam construction begins in Egypt
- January 14 - Reserve bank and Commonwealth Bank are created
- January 21 - Mine collapses at Coalbrook, South Africa - 437 dead
- January 22 - In France, president Charles de Gaulle fires Jacques Massun, commander-in-chief for the French troops in Algeria
- January 22-23 - Jacques Piccard and Donald Walsh descend into the Marianas Trench in the bathyscape Trieste, reaching the depth of 10.916 meters
- January 23 - Jacques Piccard and Don Walsh in the bathyscaphe USS Trieste break a depth record when they descend to the bottom of Challenger Deep 35,820 feet (10,750 meters) below sea level in the Pacific Ocean
- January 24 - A major insurrection in Algiers against French colonial policy
- January 25 - The National Association of Broadcasters reacts to the Payola scandal by threatening fines for any disc jockeys who accepted money for playing particular records
- February 1 - In Greensboro, N.C., four black students from North Carolina Agricultural and Technical College begin a sit-in at a segregated Woolworth's lunch counter. Although they are refused service, they are allowed to stay at the counter. The event triggers many similar nonviolent protests throughout the South, and six months later the original four protesters are served lunch at the same counter.
- February 5 - Particle accelerator of CERN inaugurated in Geneve, Switzerland
- February 8-February 9 - Adolph Coors II killed during an attempt to kidnap him in Colorado. Joseph Corbett Jr is arrested next October
- February 9 - Joanne Woodward receives the first star on the Hollywood Walk of Fame
- February 9 - Adolph Coors III, chairman of the board of the Coors Brewing Company, is kidnapped and captors demand $500,000. Coors is later found dead and Joseph Corbett Jr is indicted.
- February 10 - In Brussels, conference about Congo independence begins
- February 11 - 12 Indian soldiers die in clashes with Chinese troops at the border
- February 11 - The airship ZPG-3W is destroyed in a storm in Massachusetts
- February 13 - Nuclear testing: France tests its first atomic bomb in Sahara
- February 18 - 1960 Winter Olympics open in Squaw Valley, California.
- February 29-March 1 night - Earthquake totally destroys Agadir, Morocco.

March-April

Morocco
- March 6 - Vietnam War: The United States announces that 3,500 American soldiers are going to be sent to Vietnam
- March 6 - Canton of Geneve in Switzerland gives women the right to vote
- March 21 - Apartheid: Massacre in Sharpeville, South Africa: Afrikaner police open fire on a group of unarmed black South African demonstrators, killing 69 and wounding 180.
- March 22 - Arthur Leonard Schawlow & Charles Hard Townes receive the first patent for a laser.
- April 1 - Tuanku Abdul Rahman ibni Almarhum Tuanku Muhammad, 1st Yang di-Pertuan Agong of Malaysia dies in office. He is replaced by Hisamuddin Alam Shah ibni Almarhum Sultan Alaeddin Sulaiman Shah, Sultan of Selangor.
- April 1 - The United States launches the first weather satellite, TIROS-1
- April 4 - First three female priests ordained in Sweden
- April 9 - Gunman attacks South African Prime Minister Verwoerd in Johannesburg and wounds him seriously
-

Communications satellite

History

Early missions

Geostationary orbits

Low-Earth-orbiting satellites

Molniya satellites

Applications

Telephony

Television and Radio

Mobile satellite technologies

Amateur radio

Satellite Broadband

See also

External links

Telecommunications

Examples of human (tele)communications

See also

External links

Molniya orbit

Properties

Use in communications

Other uses

Derivation

References

See also

Fiber optic

Optical description

Optical fiber communication

Comparison with electrical transmission

Other uses of optical fibers

Manufacture

Optical fiber cables

History

References

See also

External links

Project SCORE

External link

Store and forward

References

See also

NASA

Vision and mission

History

Space Race

Apollo program

Other early missions

Shuttle era

NASA's future

Criticisms

NASA spaceflight missions

Human spaceflight

Robotic space missions

List of NASA administrators

Field installations

Awards and decorations

Related legislation

See also

Other space agencies

External links

General

Further research

Echo satellite

Echo 1

Echo 2

See also

Source

1960

Events

January-February

March-April