Distance measuring equipment
Distance measuring equipment is a radio navigation technology that measures the slant range between an aircraft and a ground station by timing the propagation delay of radio signals in the frequency band between 960 and 1215 megahertz. Line-of-visibility between the aircraft and ground station is required. An interrogator initiates an exchange by transmitting a pulse pair, on an assigned ‘channel’, to the transponder ground station; the channel assignment specifies the spacing between the pulses. After a known delay, the transponder replies by transmitting a pulse pair on a frequency, offset from the interrogation frequency by 63 MHz and having specified separation. DME systems are used worldwide; some countries require that aircraft operating under instrument flight rules be equipped with a DME interrogator. In some other countries, a DME interrogator is only required for conducting certain operations. While stand-alone DME transponders are permitted, DME transponders are paired with an azimuth guidance system to provide aircraft with a two-dimensional navigation capability.
A common combination is a DME colocated with a VOR transmitter in a single ground station. When this occurs, the frequencies of the VOR and DME equipment are paired; such a configuration enables an aircraft to determine its azimuth angle and distance from the station. A VORTAC installation provides the same capabilities to civil aircraft but provides 2-D navigation capabilities to military aircraft. Low-power DME transponders are associated with some ILS, ILS localizer and MLS installations. In those situations, the DME transponder frequency/pulse spacing is paired with the ILS, LOC or MLS frequency. ICAO characterizes DME transmissions as ultra high frequency; the term L-band is used. Developed in Australia, DME was invented by James "Gerry" Gerrand under the supervision of Edward George "Taffy" Bowen while employed as Chief of the Division of Radiophysics of the Commonwealth Scientific and Industrial Research Organisation. Another engineered version of the system was deployed by Amalgamated Wireless Australasia Limited in the early 1950s operating in the 200 MHz VHF band.
This Australian domestic version was referred to by the Federal Department of Civil Aviation as DME, the international version adopted by ICAO as DME. DME is similar in principle to secondary radar ranging function, except the roles of the equipment in the aircraft and on the ground are reversed. DME was a post-war development based on the IFF systems of World War II. To maintain compatibility, DME is functionally identical to the distance measuring component of TACAN. In their intended use, aircraft employ DME to determine their distance from a land-based transponder by sending and receiving pulse pairs; the ground stations are collocated with VORs or VORTACs. A low-power DME can be collocated with an Instrument Landing System, ILS localizer, or Microwave landing system where it provides an accurate distance to touchdown, similar to that otherwise provided by ILS marker beacons. A newer role for DMEs is DME/DME area navigation. Owing to the superior accuracy of DME relative to VOR, navigation using two DMEs permits operations that navigating with VOR/DME does not.
However, it requires that the aircraft have RNAV capabilities, some operations require an inertial reference unit. A typical DME ground transponder for en-route or terminal navigation will have a 1 kW peak pulse output on the assigned UHF channel; the DME system comprises a UHF transmitter/receiver in the aircraft and a UHF receiver/transmitter on the ground. SEARCH MODE: 150 interrogation pulse-pairs per second; the aircraft interrogates the ground transponder with a series of pulse-pairs and, after a precise time delay, the ground station replies with an identical sequence of pulse-pairs. The DME receiver in the aircraft searches for reply pulse-pairs with the correct interval and reply pattern to its original interrogation pattern.. TRACK MODE: less than 30 interrogation Pulse-pairs per second, as the average number of pulses in SEARCH and TRACK is limited to max 30 pulse pairs per second; the aircraft interrogator locks on to the DME ground station once it recognizes a particular reply pulse sequence has the same spacing as the original interrogation sequence.
Once the receiver is locked on, it has a narrower window in which to look for the echoes and can retain lock. A radio signal takes 12.36 microseconds to travel 1 nautical mile to the target and back—also referred to as a radar-mile. The time difference between interrogation and reply, minus the 50 microsecond ground transponder delay, is measured by the interrogator's timing circuitry and converted to a distance measurement, in nautical miles displayed on the cockpit DME display; the distance formula, distance = rate * time, is used by the DME receiver to calculate its distance from the DME ground station. The rate in the calculation is the velocity of the rad
Beacon
A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which provides a fixed location that can used to navigate around obsticals or into port. More modern examples include a variety of radio beacons that can be read on radio direction finders in all weather, radar transponders that appear on radar displays. Beacons can be combined with semaphoric or other indicators to provide important information, such as the status of an airport, by the colour and rotational pattern of its airport beacon, or of pending weather as indicated on a weather beacon mounted at the top of a tall building or similar site; when used in such fashion, beacons can be considered a form of optical telegraphy. Beacons help guide navigators to their destinations. Types of navigational beacons include radar reflectors, radio beacons and visual signals. Visual beacons range from small, single-pile structures to large lighthouses or light stations and can be located on land or on water.
Lighted beacons are called lights. Aerodrome beacons are used to indicate locations of helipads. Handheld beacons are employed in aircraft marshalling, are used by the marshal to deliver instructions to the crew of aircraft as they move around an active airport, heliport or aircraft carrier. Classically, beacons were fires lit at well-known locations on hills or high places, used either as lighthouses for navigation at sea, or for signalling over land that enemy troops were approaching, in order to alert defenses; as signals, beacons were part of a relay league. Systems of this kind have existed for centuries over much of the world; the ancient Greeks called them phryctoriae, while beacons figure on several occasions on the column of Trajan. In the 10th century, during the Arab–Byzantine wars, the Byzantine Empire used a beacon system to transmit messages from the border with the Abbasid Caliphate, across Anatolia to the imperial palace in the Byzantine capital, Constantinople, it was devised by Leo the Mathematician for Emperor Theophilos, but either abolished or radically curtailed by Theophilos' son and successor, Michael III.
Beacons were used in Greece as well, while the surviving parts of the beacon system in Anatolia seem to have been reactivated in the 12th century by Emperor Manuel I Komnenos. In Scandinavia many hill forts were part of beacon networks to warn against invading pillagers. In Finland, these beacons were called vainovalkeat, "persecution fires", or vartiotulet, "guard fires", were used to warn Finn settlements of imminent raids by the Vikings. In Wales, the Brecon Beacons were named for beacons used to warn of approaching English raiders. In England, the most famous examples are the beacons used in Elizabethan England to warn of the approaching Spanish Armada. Many hills in England were named Beacon Hill after such beacons. In England the authority to erect beacons lay wirh the King and was deligated to the Lord High Admiral; the money due for the maintenance of beacons was called Beaconagium and was levied by the sheriff of each county. In the Scottish borders country, a system of beacon fires was at one time established to warn of incursions by the English.
Hume and Eggerstone castles and Soltra Edge were part of this network. The Great Wall of China is a beacon network. In Spain, the border of Granada in the territory of the Crown of Castile had a complex beacon network to warn against Moorish raiders and military campaigns. Vehicular beacons are rotating or flashing lights affixed to the top of a vehicle to attract the attention of surrounding vehicles and pedestrians. Emergency vehicles such as fire engines, police cars, tow trucks, construction vehicles, snow-removal vehicles carry beacon lights; the color of the lamps varies by jurisdiction. Beacons may be constructed with halogen bulbs similar to those used in vehicle headlamps, xenon flashtubes, or LEDs. Incandescent and xenon light sources require the vehicle's engine to continue running to ensure that the battery is not depleted when the lights are used for a prolonged period; the low power consumption of LEDs allows the vehicle's engine to remain turned off while the lights operate nodes.
Beacons and bonfires are used to mark occasions and celebrate events. The Mishna describes a system of fire beacons used by the high court in Jerusalem to communicate the declaration of a new month to Jews in Israel and Babylon. Beacons have allegedly been abused by shipwreckers. An illicit fire at a wrong position would be used to direct a ship against shoals or beaches, so that its cargo could be looted after the ship sank or ran aground. There are, however, no substantiated occurrences of such intentional shipwrecking. In wireless networks, a beacon is a type of frame, sent by the access point to indicate that it is on. Bluetooth based beacons periodically send out a data packet and this could be used by software to identify the beacon location; this is used by indoor navigation and positioning applications. Beaconing is the process; the stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token FDDI networks. In Aeschylus' tragedy Agamemnon, a chain of eight beacons manned by so-called lampadóphoroi inform Clytemnestra in Argos, within
Two-way radio
A two-way radio is a radio that can both transmit and receive a signal, unlike a broadcast receiver which only receives content. It is an audio transceiver designed for bidirectional person-to-person voice communication with other users with similar radios using the same radio frequency. Two-way radios are available in stationary base and hand-held portable configurations. Hand-held two-way radios are called walkie-talkies, handie-talkies or hand-helds. Two-way radio systems operate in a half-duplex mode: the operator can talk, or he can listen, but not at the same time. A push-to-talk or Press To Transmit button activates the transmitter. Other Full-duplex is achieved by the use of two different frequencies or by frequency-sharing methods to carry the two directions of the conversation simultaneously. Methods for mitigating the self interference caused by simultaneous transmission and reception on different but close-spaced frequencies include using two antennas, or dynamic solid-state filters.
Time-division technologies are used for mitigating self interference by simultaneous transmission and reception on the same frequency. Installation of receivers and transmitters at the same fixed location allowed exchange of messages wirelessly; as early as 1907, two-way telegraphy traffic across the Atlantic Ocean was commercially available. By 1912, commercial and military ships carried both transmitters and receivers, allowing two-way communication in close to real-time with a ship, out of sight of land; the first mobile two-way radio was developed in Australia in 1923 by Senior Constable Frederick William Downie of the Victorian Police. The Victoria Police were the first in the world to use wireless communication in cars, putting an end to the inefficient status reports via public telephone boxes, used until that time; the first sets took up the entire back seat of the Lancia patrol cars. As radio equipment became more powerful and easier to use, smaller vehicles had two-way radio communication equipment installed.
Installation of radio equipment in aircraft allowed scouts to report back observations in real-time, not requiring the pilot to drop messages to troops on the ground below or to land and make a personal report. In 1933, the Bayonne, New Jersey police department operated a two-way system between a central fixed station and radio transceivers installed in police cars. During World War II walkie-talkie hand-held radio transceivers were extensively used by air and ground troops, both by the Allies and the Axis. Early two-way schemes allowed only one station to transmit at a time while others listened, since all signals were on the same radio frequency – this was called "simplex" mode. Code and voice operations required a simple communication protocol to allow all stations to cooperate in using the single radio channel, so that one station's transmissions were not obscured by another's. By using receivers and transmitters tuned to different frequencies and solving the problems introduced by operation of a receiver next to a transmitter, simultaneous transmission and reception was possible at each end of a radio link, in so-called "full duplex" mode.
The first radio systems could not transmit voice. This required training of operators in use of Morse code. On a ship, the radio operating officers had no other duties than handling radio messages; when voice transmission became possible, dedicated operators were no longer required and two-way radio use became more common. Today's two-way mobile radio equipment is nearly as simple to use as a household telephone, from the point of view of operating personnel, thereby making two-way communications a useful tool in a wide range of personal and military roles. Two-way radio systems can be classified in several ways depending on their attributes. Conventional radios operate on fixed RF channels. In the case of radios with multiple channels, they operate on one channel at a time; the proper channel is selected by a user. The user operates a channel selector on the radio control panel to pick the appropriate channel. In multi-channel systems, channels are used for separate purposes. A channel may be reserved for a geographic area.
In a functional channel system, one channel may allow City of Springfield road repair crews to talk to the City of Springfield's road maintenance office. A second channel may allow road repair crews to communicate with state highway department crews. In a wide-area or geographic system, a taxi company may use one channel to communicate in the Boston, Massachusetts area and a second channel when taxis are in Providence, Rhode Island; this is referred to as Multisite operation. In this case, the driver or the radio must switch channels to maintain coverage when transitioning between each area. Most modern conventional digital radios and systems are capable of automatic "roaming" where the radio automatically switches channels on a dynamic basis; the radio accomplishes this based on the received signal strength of the radio repeater's recurring "beacon" signal and a "site" or "roam" list that identifies available geographic channels. Some analog conventional systems can be equipped with a feature called "vote-scan" that provides more limited roaming.
Radio "simulcast" technology can be used in adjacent areas, where each site is equipped with the same channel. Here, the transmitters must be synchronized, a centralized voter or receiver comparator device is required to select the best quality sign
Amateur radio
Amateur radio known as ham radio, describes the use of radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport and emergency communication. The term "amateur" is used to specify "a duly authorised person interested in radioelectric practice with a purely personal aim and without pecuniary interest; the amateur radio service is established by the International Telecommunication Union through the Radio Regulations. National governments regulate technical and operational characteristics of transmissions and issue individual stations licenses with an identifying call sign. Prospective amateur operators are tested for their understanding of key concepts in electronics and the host government's radio regulations. Radio amateurs use a variety of voice, text and data communications modes and have access to frequency allocations throughout the RF spectrum; this enables communication across a city, country, the world, or into space.
In many countries, amateur radio operators may send, receive, or relay radio communications between computers or transceivers connected to secure virtual private networks on the Internet. Amateur radio is represented and coordinated by the International Amateur Radio Union, organized in three regions and has as its members the national amateur radio societies which exist in most countries. According to an estimate made in 2011 by the American Radio Relay League, two million people throughout the world are involved with amateur radio. About 830,000 amateur radio stations are located in IARU Region 2 followed by IARU Region 3 with about 750,000 stations. A smaller number, about 400,000, are located in IARU Region 1; the origins of amateur radio can be traced to the late 19th century, but amateur radio as practiced today began in the early 20th century. The First Annual Official Wireless Blue Book of the Wireless Association of America, produced in 1909, contains a list of amateur radio stations.
This radio callbook lists wireless telegraph stations in Canada and the United States, including 89 amateur radio stations. As with radio in general, amateur radio was associated with various amateur experimenters and hobbyists. Amateur radio enthusiasts have contributed to science, engineering and social services. Research by amateur operators has founded new industries, built economies, empowered nations, saved lives in times of emergency. Ham radio can be used in the classroom to teach English, map skills, math and computer skills; the term "ham" was first a pejorative term used in professional wired telegraphy during the 19th century, to mock operators with poor Morse code sending skills. This term continued to be used after the invention of radio and the proliferation of amateur experimentation with wireless telegraphy; the use of "ham" meaning "amateurish or unskilled" survives today in other disciplines. The amateur radio community subsequently began to reclaim the word as a label of pride, by the mid-20th century it had lost its pejorative meaning.
Although not an acronym, it is mistakenly written as "HAM" in capital letters. The many facets of amateur radio attract practitioners with a wide range of interests. Many amateurs begin with a fascination of radio communication and combine other personal interests to make pursuit of the hobby rewarding; some of the focal areas amateurs pursue include radio contesting, radio propagation study, public service communication, technical experimentation, computer networking. Amateur radio operators use various modes of transmission to communicate; the two most common modes for voice transmissions are single sideband. FM offers high quality audio signals, while SSB is better at long distance communication when bandwidth is restricted. Radiotelegraphy using Morse code known as "CW" from "continuous wave", is the wireless extension of landline telegraphy developed by Samuel Morse and dates to the earliest days of radio. Although computer-based modes and methods have replaced CW for commercial and military applications, many amateur radio operators still enjoy using the CW mode—particularly on the shortwave bands and for experimental work, such as earth-moon-earth communication, because of its inherent signal-to-noise ratio advantages.
Morse, using internationally agreed message encodings such as the Q code, enables communication between amateurs who speak different languages. It is popular with homebrewers and in particular with "QRP" or very-low-power enthusiasts, as CW-only transmitters are simpler to construct, the human ear-brain signal processing system can pull weak CW signals out of the noise where voice signals would be inaudible. A similar "legacy" mode popular with home constructors is amplitude modulation, pursued by many vintage amateur radio enthusiasts and aficionados of vacuum tube technology. Demonstrating a proficiency in Morse code was for many years a requirement to obtain an amateur license to transmit on frequencies below 30 MHz. Following changes in international regulations in 2003, countries are no longer required to demand proficiency; the United States Federal
Radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth. Like radiolocation, it is a type of radiodetermination; the basic principles are measurements from/to electric beacons Angular directions, e.g. by bearing, radio phases or interferometry, Distances, e.g. ranging by measurement of time of flight between one transmitter and multiple receivers or vice versa, Distance differences by measurement of times of arrival of signals from one transmitter to multiple receivers or vice versa Partly velocity, e.g. by means of radio Doppler shift. Combinations of these measurement principles are important—e.g. Many radars measure azimuth of a target; these systems used some form of directional radio antenna to determine the location of a broadcast station on the ground. Conventional navigation techniques are used to take a radio fix; these were introduced prior to World War I, remain in use today. The first system of radio navigation was the Radio Direction Finder, or RDF.
By tuning in a radio station and using a directional antenna, one could determine the direction to the broadcasting antenna. A second measurement using another station was taken. Using triangulation, the two directions can be plotted on a map where their intersection reveals the location of the navigator. Commercial AM radio stations can be used for this task due to their long range and high power, but strings of low-power radio beacons were set up for this task near airports and harbours. Early RDF systems used a loop antenna, a small loop of metal wire, mounted so it can be rotated around a vertical axis. At most angles the loop has a flat reception pattern, but when it is aligned perpendicular to the station the signal received on one side of the loop cancels the signal in the other, producing a sharp drop in reception known as the "null". By rotating the loop and looking for the angle of the null, the relative bearing of the station can be determined. Loop antennas can be seen on most pre-1950s aircraft and ships.
The main problem with RDF is that it required a special antenna on the vehicle, which may not be easy to mount on smaller vehicles or single-crew aircraft. A smaller problem is that the accuracy of the system is based to a degree on the size of the antenna, but larger antennas would make the installation more difficult. During the era between World War I and World War II, a number of systems were introduced that placed the rotating antenna on the ground; as the antenna rotated through a fixed position due north, the antenna was keyed with the morse code signal of the station's identification letters so the receiver could ensure they were listening to the right station. They waited for the signal to either peak or disappear as the antenna pointed in their direction. By timing the delay between the morse signal and the peak/null dividing by the known rotational rate of the station, the bearing of the station could be calculated; the first such system was the German Telefunken Kompass Sender, which began operations in 1907 and was used operationally by the Zeppelin fleet until 1918.
An improved version was introduced by the UK as the Orfordness Beacon in 1929 and used until the mid-1930s. A number of improved versions followed, replacing the mechanical motion of the antennas with phasing techniques that produced the same output pattern with no moving parts. One of the longest lasting examples was Sonne, which went into operation just before World War II and was used operationally under the name Consol until 1991; the modern VOR system is based on the same principles. A great advance in the RDF technique was introduced in the form of phase comparisons of a signal as measured on two or more small antennas, or a single directional solenoid; these receivers were smaller, more accurate, simpler to operate. Combined with the introduction of the transistor and integrated circuit, RDF systems were so reduced in size and complexity that they once again became quite common during the 1960s, were known by the new name, automatic direction finder, or ADF; this led to a revival in the operation of simple radio beacons for use with these RDF systems, now referred to as non-directional beacons.
As the LF/MF signals used by NDBs can follow the curvature of earth, NDB has a much greater range than VOR which travels only in line of sight. NDB can be categorized as short range depending on their power; the frequency band allotted to non-directional beacons is 190–1750 kHz, but the same system can be used with any common AM-band commercial station. VHF omnidirectional range, or VOR, is an implementation of the reverse-RDF system, but one, more accurate and able to be automated. Instead of a single signal, the VOR transmitter sends out three signals – one is a simple voice channel that sends morse code to identify the station, another is a continuous signal sent in all directions, the last is a signal, rotated at 30 RPM. Like the Orfordness concept, the bearing of the station is measured by finding the rotating signal's peak or null, but instead of timing the signal, the rotating signal is changed in phase in synchronicity with its rotation, such that it is in-phase when pointed north, 90 degrees off when it points east, so forth.
By comparing the phase of the received signal with the one being broadcast omnidirectionally, the angle can be determined using simple electronics. This angle is displayed in the cockpit of the aircraft, can be used to take a fix just like the earlier RDF systems, although it is easier to use; as VOR required two VHF receivers as well as a conventional radio for station identification, the system did not becom
Search and rescue
Search and rescue is the search for and provision of aid to people who are in distress or imminent danger. The general field of search and rescue includes many specialty sub-fields determined by the type of terrain the search is conducted over; these include mountain rescue. International Search and Rescue Advisory Group is a UN organization that promotes the exchange of information between national urban search and rescue organizations; the duty to render assistance is covered by Article 98 of the UNCLOS. There are many different definitions of search and rescue, depending on the agency involved and country in question. Canadian Forces: "Search and Rescue comprises the search for, provision of aid to, ships or other craft which are, or are feared to be, in distress or imminent danger." United States Coast Guard: "The use of available resources to assist persons or property in potential or actual distress." United States Defense Department: A search is "an operation coordinated by a Rescue Coordination Center or rescue sub-center, using available personnel and facilities to locate persons in distress" and rescue is "an operation to retrieve persons in distress, provide for their initial medical or other needs, deliver them to a place of safety".
One of the world's earliest well-documented SAR efforts ensued following the 1656 wreck of the Dutch merchant ship Vergulde Draeck off the west coast of Australia. Survivors sought help, in response three separate SAR missions were conducted, without success. On 29 November 1945, a Sikorsky R-5 performed the first civilian helicopter rescue operation in history, with Sikorsky's chief pilot Dmitry "Jimmy" Viner in the cockpit, using an experimental hoist developed jointly by Sikorsky and Breeze. All 5 crew members of an oil barge, which had run aground on Penfield Reef, were saved before the barge sank. In 1983, Korean Air Lines Flight 007 with 269 occupants was shot down by a Soviet aircraft near Sakhalin; the Soviets sent SAR helicopters and boats to Soviet waters, while a search and rescue operation was initiated by U. S. South Korean, Japanese ships and aircraft in international waters, but no survivors were found. In July 2009, Air France Flight 447 was lost in the middle of the Atlantic Ocean.
An international SAR effort was launched, to no avail. A third effort nearly two years discovered the crash site and recovered the flight recorders. In early 2014, Malaysia Airlines Flight 370 crashed under mysterious circumstances. Many nations contributed to the initial SAR effort, fruitless. In June 2014, the Australian Transport Safety Bureau commissioned the MV Fugro Equator to lead a three-month survey of the ocean bed, for which it had budgeted $60mn; the search for Flight 370 has become the largest SAR so far with the largest budget. Ground search and rescue is the search for persons who are lost or in distress on land or inland waterways. People may go missing for a variety of reasons; some may disappear voluntarily, due to issues like domestic abuse. Others disappear for involuntary reasons such as mental illness, getting lost, an accident, death in a location where they cannot be found or, less due to abduction. Ground search and rescue missions that occur in urban areas should not be confused with "urban search and rescue", which in many jurisdictions refers to the location and extraction of people from collapsed buildings or other entrapments.
In most countries, the police are the primary agency for carrying out searches for a missing person on land. Some places have voluntary search and rescue teams that can be called out to assist these searches. Mountain rescue relates to search and rescue operations in rugged and mountainous terrain. Cave rescue is a specialized form of rescue for rescuing injured, trapped or lost cave explorers. Urban search and rescue referred to as Heavy Urban Search and Rescue, is the location and rescue of persons from collapsed buildings or other urban and industrial entrapments. Due to the specialized nature of the work, most teams are multi-disciplinary and include personnel from police and emergency medical services. Unlike traditional ground search and rescue workers, most US&R responders have basic training in structural collapse and the dangers associated with live electrical wires, broken natural gas lines and other hazards. While earthquakes have traditionally been the cause of US&R operations, terrorist attacks and extreme weather such as tornadoes and hurricanes have resulted in the deployment of these resources.
Combat search and rescue is search and rescue operations that are carried out during war that are within or near combat zones. Maritime search and rescue is carried out at sea to save sailors and passengers in distress, or the survivors of downed aircraft; the type of agency which carries out maritime search and rescue varies by country. When a distressed or missing vessel is located, these organizations deploy lifeboats to return them to land. In some cases, the agencies may carry out an air-sea rescue; this refers to the combined use of aircraft and surface vessels. NationalThe Australian search and rescue service is provided by AusSAR, part of the Australian Maritime Safety Authority. AusSAR operates a 24-hour Rescue Coordination Centre in Canbe
Iridium Communications
Iridium Communications Inc. is a publicly traded American company headquartered in McLean, Virginia. Iridium operates the Iridium satellite constellation, a system of 141 active satellites used for worldwide voice and data communication from hand-held satellite phones and other transceiver units; the Iridium network is unique in that it covers the whole Earth, including poles and airways, with 95 satellites launched so far. The satellites are visible in the night sky as satellite flares, a phenomenon observed as short-lived bright flashes of light. Iridium manages several operations centers, including Tempe and Leesburg, United States; the U. S. Department of Defense, through its own dedicated gateway, relies on Iridium for global communications capabilities; the company derives its name from the chemical element iridium which has an atomic number of 77, equalling the initial number of satellites which were planned to be deployed. The Iridium communications service was launched on November 1, 1998 by what was Iridium SSC.
The first Iridium call was made by Vice President of the United States Al Gore to Gilbert Grosvenor, the great-grandson of Alexander Graham Bell and chairman of the National Geographic Society. Motorola provided major financial backing; the logo of the company represents the Big Dipper. The founding company went into Chapter 11 bankruptcy nine months on August 13, 1999; the handsets could not operate as promoted until the entire constellation of satellites was in place, requiring a massive initial capital cost running into the billions of dollars. The cost of service was prohibitive for many users, reception indoors was difficult and the bulkiness and expense of the hand held devices when compared to terrestrial cellular mobile phones discouraged adoption among potential users. Mismanagement is another major factor cited in the original program's failure. In 1999, CNN writer David Rohde detailed how he applied for Iridium service and was sent information kits, but was never contacted by a sales representative.
He encountered programming problems on Iridium's website, a "run-around" from the company's representatives. After Iridium filed bankruptcy, it cited "difficulty gaining subscribers"; the initial commercial failure of Iridium had a damping effect on other proposed commercial satellite constellation projects, including Teledesic. Other schemes followed Iridium into bankruptcy protection, while a number of other proposed schemes were never constructed. In August 2000, Motorola announced. In December 2000 the US government stepped in to save Iridium by providing $72 million in exchange for a two-year contract and approving the fire-sale of the company from US Bankruptcy court for $25 million, in March 2001; this erased over $4 billion in debt. Iridium service was restarted in 2001 by the newly founded Iridium Satellite LLC, owned by a group of private investors. Although the satellites and other assets and technology behind Iridium were estimated to have cost around US$6 billion, the investors bought the firm for about US$35 million.
On February 10, 2009, Iridium 33 collided with a defunct Russian satellite, Kosmos 2251, 800 kilometres over Siberia. Two large debris clouds were created. Iridium replaced its original constellation by sending 75 new Iridium satellites into space on a SpaceX Falcon 9 rockets; the campaign consisted of upgrades to the Iridium Gateway and Command & Control ground facilities. The Iridium NEXT launch campaign was announced in 2007. Within three years, Iridium began work on the satellites and launch program. In June 2010, Iridium announced a fixed-price contract with Thales Alenia Space for the design and construction of the next-generation satellites for the upgraded constellation. Two weeks Iridium announced a $492 million contract designated the Falcon 9 as a major provider of launch services for the Iridium NEXT campaign, becoming the largest single commercial launch deal signed. On January 14, 2017, 10 years after the campaign was first announced, the first of eight Iridium NEXT launches took place with SpaceX from Vandenberg Air Force Base in California.
Over the next two years, Iridium sent an additional 65 satellites into Low-Earth Orbit to replace the original satellite constellation. This program was the first retroactive replacement program in history, taking place without disrupting existing Iridium service; the final Iridium NEXT launch took place on January 11, 2019, less than 2 years after the first launch. Iridium Satellite LLC merged with a special purpose acquisition company created by the investment bank Greenhill & Co. in September 2009 to create Iridium Communications Inc. The public company trades on NASDAQ under the symbol "IRDM"; the company surpassed 1 million subscribers in March 2018. Revenue for the full year 2018 was US $523.0 million with operational EBITDA of US$302.0 million, a 14% increase from $265.6 million in the prior year. The system is being used extensively by the U. S. Department of Defense through the DoD Gateway; the commercial services gateway in Tempe, provides voice and data services for commercial customers on a global basis.
Iridium targets maritime, land mobile, IoT markets, in addition to supporting their government customers. Matt Desch is the CEO of Iridium LLC. Iridium is a founding member of the Hosted Payload Alliance, a satellite industry alliance formed to increase awareness of the benefits of
