A pilot logbook is a record of a pilot's flying hours. It contains every flight a pilot has flown, including flight time, number of landings, types of instrument approaches made. Pilots log simulator time, as it counts towards training. In most countries, pilots are required to maintain a logbook, per their government's aviation regulations; the primary purpose is to show that certain requirements have been met for a certificate or rating, for currency purposes. In the United States, a pilot is required to log all flight time, used to meet the minimum requirements for a certificate, flight review, or instrument proficiency check, for currency; this means that a pilot does not need to record every single one of her flights. The Federal Aviation Administration does not require the flights logged to be logged in an official logbook or format, so long as the conditions CFR Title 14 §61.51 paragraph b are met. This requires information about the flight, such as date, total time, locations of takeoff and landing, information regarding pilot in command, etc.
Because the FAA does not require an official logbook or official format, many different formats are available to pilots. Some pilots use digital methods, such as recording this information in Microsoft Excel or a similar spreadsheet, or through online or other digital methods of recording their flights. Logbook
A flight recorder is an electronic recording device placed in an aircraft for the purpose of facilitating the investigation of aviation accidents and incidents. Flight recorders are known by the misnomer black box—they are in fact bright orange to aid in their recovery after accidents. There are two different flight recorder devices: the flight data recorder preserves the recent history of the flight through the recording of dozens of parameters collected several times per second; the two devices may be combined in a single unit. Together, the FDR and CVR give an accurate testimony, narrating the aircraft's flight history, to assist in any investigation; the two flight recorders are required by international regulation, overseen by the International Civil Aviation Organization, to be capable of surviving the conditions to be encountered in a severe aircraft accident. For this reason, they are specified to withstand an impact of 3400 g and temperatures of over 1,000 °C, as required by EUROCAE ED-112.
They have been a mandatory requirement in commercial aircraft in the United States since 1967. After the unexplained disappearance of Malaysia Airlines Flight 370 in 2014, commentators have called for live streaming of data to the ground, as well as extending the battery life of the underwater locator beacons. One of the earliest and proven attempts was made by François Hussenot and Paul Beaudouin in 1939 at the Marignane flight test center, with their "type HB" flight recorder; the latent image was made by a thin ray of light deviated by a mirror tilted according to the magnitude of the data to record. A pre-production run of 25 "HB" recorders was ordered in 1941 and HB recorders remained in use in French flight test centers well into the 1970s. In 1947, Hussenot founded the Société Française des Instruments de Mesure with Beaudouin and another associate, so as to market his invention, known as the "hussenograph"; this company went on to become a major supplier of data recorders, used not only aboard aircraft but trains and other vehicles.
SFIM is still present on the flight recorder market. The advantage of the film technology was that it could be developed afterwards and provides a durable, visual feedback of the flight parameters without needing any playback device. On the other hand, unlike magnetic tapes or flash memory-based technology, a photographic film cannot be erased and recycled, so it must be changed periodically; as such, this technology was reserved for one-shot uses during planned test flights. The cockpit conversation was not recorded. Another form of flight data recorder was developed in the UK during World War II. Len Harrison and Vic Husband developed a unit that could withstand a crash and fire to keep the flight data intact; this unit used copper foil as the recording medium with various styli indicating various instruments / aircraft controls which indented the copper foil. The copper foil was periodically advanced at set periods of time therefore giving a history of the instruments / control settings of the aircraft.
This unit was developed at Farnborough for the Ministry of Aircraft Production. At the war's end the Ministry got Harrison and Husband to sign over their invention to it and the Ministry patented it under British patent 19330/45; this unit was the forerunner of today's recorders being able to withstand conditions that aircrew could not. The first modern flight data recorder, called "Mata Hari", was created in 1942 by Finnish aviation engineer Veijo Hietala; this black high-tech mechanical box was able to record all important details during test flights of fighter aircraft that the Finnish army repaired or built in its main aviation factory in Tampere, Finland. During World War II both British and American air forces experimented with aircraft voice recorders. In August 1943 the USAAF conducted an experiment with a magnetic wire recorder to capture the inter-phone conversations of a B-17 bomber flight crew on a combat mission over Nazi-occupied France; the recording was broadcast back to the United States by radio two days afterwards.
In 1953, while working at the Aeronautical Research Laboratories of the Defence Science and Technology Organisation, in Melbourne, Australian research scientist David Warren conceived a device that would record not only the instrument readings, but the voices in the cockpit. In 1954 he published a report entitled "A Device for Assisting Investigation into Aircraft Accidents". Warren built a prototype FDR called "The ARL Flight Memory Unit" in 1956, in 1958 he built the first combined FDR/CVR prototype, designed with civilian aircraft in mind, for explicit post-crash examination purposes. Aviation authorities from around the world were uninterested at first, but this changed in 1958 when Sir Robert Hardingham, the Secretary of the British Air Registration Board, visited the ARL and was introduced to David Warren. Hardingham realised the significance of the invention and arranged for Warren to demonstrate the prototype in the UK; the ARL assigned an engineering team to help Warren develop the prototype to airborne stage.
The team, consisting of electronics engineers Lane Sear, Wally Boswell and Ken Fraser, developed a working design that incorporated a fire-resistant and shockproof case, a reliable system for encoding and recording aircr
A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying passengers or goods, or in support of specialized missions, such as defense and fishing. A "ship" was a sailing vessel with at least three square-rigged masts and a full bowsprit. Ships are distinguished from boats, based on size, load capacity, tradition. Ships have been important contributors to human commerce, they have supported the spread of colonization and the slave trade, but have served scientific and humanitarian needs. After the 15th century, new crops that had come from and to the Americas via the European seafarers contributed to the world population growth. Ship transport is responsible for the largest portion of world commerce; as of 2016, there were more than 49,000 merchant ships, totaling 1.8 billion dead weight tons. Of these 28% were oil tankers, 43% were bulk carriers, 13% were container ships. Ships are larger than boats, but there is no universally accepted distinction between the two.
Ships can remain at sea for longer periods of time than boats. A legal definition of ship from Indian case law is a vessel. A common notion is, but not vice versa. A US Navy rule of thumb is that ships heel towards the outside of a sharp turn, whereas boats heel towards the inside because of the relative location of the center of mass versus the center of buoyancy. American and British 19th Century maritime law distinguished "vessels" from other craft. In the Age of Sail, a full-rigged ship was a sailing vessel with at least three square-rigged masts and a full bowsprit. A number of large vessels are referred to as boats. Submarines are a prime example. Other types of large vessel which are traditionally called boats are Great Lakes freighters and ferryboats. Though large enough to carry their own boats and heavy cargoes, these vessels are designed for operation on inland or protected coastal waters. In most maritime traditions ships have individual names, modern ships may belong to a ship class named after its first ship.
In the northern parts of Europe and America a ship is traditionally referred to with a female grammatical gender, represented in English with the pronoun "she" if named after a man. This is not universal usage and some English language journalistic style guides advise using "it" as referring to ships with female pronouns can be seen as offensive and outdated. In many documents the ship name is introduced with a ship prefix being an abbreviation of the ship class, for example "MS" or "SV", making it easier to distinguish a ship name from other individual names in a text; the first known vessels could not be described as ships. The first navigators began to use animal skins or woven fabrics as sails. Affixed to the top of a pole set upright in a boat, these sails gave early ships range; this allowed men to explore allowing for the settlement of Oceania for example. By around 3000 BC, Ancient Egyptians knew, they used woven straps to lash the planks together, reeds or grass stuffed between the planks helped to seal the seams.
The Greek historian and geographer Agatharchides had documented ship-faring among the early Egyptians: "During the prosperous period of the Old Kingdom, between the 30th and 25th centuries BC, the river-routes were kept in order, Egyptian ships sailed the Red Sea as far as the myrrh-country." Sneferu's ancient cedar wood ship Praise of the Two Lands is the first reference recorded to a ship being referred to by name. The ancient Egyptians were at ease building sailboats. A remarkable example of their shipbuilding skills was the Khufu ship, a vessel 143 feet in length entombed at the foot of the Great Pyramid of Giza around 2500 BC and found intact in 1954, it is known that ancient Nubia/Axum traded with India, there is evidence that ships from Northeast Africa may have sailed back and forth between India/Sri Lanka and Nubia trading goods and to Persia and Rome. Aksum was known by the Greeks for having seaports for ships from Yemen. Elsewhere in Northeast Africa, the Periplus of the Red Sea reports that Somalis, through their northern ports such as Zeila and Berbera, were trading frankincense and other items with the inhabitants of the Arabian Peninsula well before the arrival of Islam as well as with Roman-controlled Egypt.
A panel found at Mohenjodaro depicted a sailing craft. Vessels were of many types; this treatise gives a technical exposition on the techniques of shipbuilding. It sets forth minute details about the various types of ships, their sizes, the materials from which they were built; the Yukti Kalpa Taru sums up in a condensed form all the available information. The Yukti Kalpa Taru gives sufficient information and dates to prove that, in ancient times, Indian shipbuilders had a good knowledge of the materials which were used in building ships. In addition to describing the qualities of the different types of wood and their suitability for shipbuilding, the Yukti Kalpa Taru gives an elaborate classification of ships based on their size; the oldest discovered sea faring hulled boat is the Late Bronze Age Uluburun shipwreck off the coast of Turkey, dating back to 1300 BC. The Phoenicians, the first to sail around
Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, spacecraft, guided missiles, motor vehicles, weather formations, terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the object. Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed. Radar was developed secretly for military use by several nations in the period before and during World War II. A key development was the cavity magnetron in the UK, which allowed the creation of small systems with sub-meter resolution; the term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging The term radar has since entered English and other languages as a common noun, losing all capitalization.
The modern uses of radar are diverse, including air and terrestrial traffic control, radar astronomy, air-defense systems, antimissile systems, marine radars to locate landmarks and other ships, aircraft anticollision systems, ocean surveillance systems, outer space surveillance and rendezvous systems, meteorological precipitation monitoring and flight control systems, guided missile target locating systems, ground-penetrating radar for geological observations, range-controlled radar for public health surveillance. High tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from high noise levels. Radar is a key technology that the self-driving systems are designed to use, along with sonar and other sensors. Other systems similar to radar make use of other parts of the electromagnetic spectrum. One example is "lidar". With the emergence of driverless vehicles, Radar is expected to assist the automated platform to monitor its environment, thus preventing unwanted incidents.
As early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895, Alexander Popov, a physics instructor at the Imperial Russian Navy school in Kronstadt, developed an apparatus using a coherer tube for detecting distant lightning strikes; the next year, he added a spark-gap transmitter. In 1897, while testing this equipment for communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation; the German inventor Christian Hülsmeyer was the first to use radio waves to detect "the presence of distant metallic objects". In 1904, he demonstrated the feasibility of detecting a ship in dense fog, but not its distance from the transmitter, he obtained a patent for his detection device in April 1904 and a patent for a related amendment for estimating the distance to the ship.
He got a British patent on September 23, 1904 for a full radar system, that he called a telemobiloscope. It operated on a 50 cm wavelength and the pulsed radar signal was created via a spark-gap, his system used the classic antenna setup of horn antenna with parabolic reflector and was presented to German military officials in practical tests in Cologne and Rotterdam harbour but was rejected. In 1915, Robert Watson-Watt used radio technology to provide advance warning to airmen and during the 1920s went on to lead the U. K. research establishment to make many advances using radio techniques, including the probing of the ionosphere and the detection of lightning at long distances. Through his lightning experiments, Watson-Watt became an expert on the use of radio direction finding before turning his inquiry to shortwave transmission. Requiring a suitable receiver for such studies, he told the "new boy" Arnold Frederic Wilkins to conduct an extensive review of available shortwave units. Wilkins would select a General Post Office model after noting its manual's description of a "fading" effect when aircraft flew overhead.
Across the Atlantic in 1922, after placing a transmitter and receiver on opposite sides of the Potomac River, U. S. Navy researchers A. Hoyt Taylor and Leo C. Young discovered that ships passing through the beam path caused the received signal to fade in and out. Taylor submitted a report, suggesting that this phenomenon might be used to detect the presence of ships in low visibility, but the Navy did not continue the work. Eight years Lawrence A. Hyland at the Naval Research Laboratory observed similar fading effects from passing aircraft. Before the Second World War, researchers in the United Kingdom, Germany, Japan, the Netherlands, the Soviet Union, the United States, independently and in great secrecy, developed technologies that led to the modern version of radar. Australia, New Zealand, South Africa followed prewar Great Britain's radar development, Hungary generated its radar technology during the war. In France in 1934, following systematic studies on the split-anode magnetron, the research branch of the Compagnie Générale de Télégraphie Sans Fil headed by Maurice Ponte with Henri Gutton, Sylvain Berline and M. Hugon, began developing an obstacle-locatin
National Archives and Records Administration
The National Archives and Records Administration is an independent agency of the United States government charged with preserving and documenting government and historical records and with increasing public access to those documents, which comprise the National Archives. NARA is responsible for maintaining and publishing the authentic and authoritative copies of acts of Congress, presidential directives, federal regulations; the NARA transmits votes of the Electoral College to Congress. The Archivist of the United States is the chief official overseeing the operation of the National Archives and Records Administration; the Archivist not only maintains the official documentation of the passage of amendments to the U. S. Constitution by state legislatures, but has the authority to declare when the constitutional threshold for passage has been reached, therefore when an act has become an amendment; the Office of the Federal Register publishes the Federal Register, Code of Federal Regulations, United States Statutes at Large, among others.
It administers the Electoral College. The National Historical Publications and Records Commission —the agency's grant-making arm—awards funds to state and local governments and private archives and universities, other nonprofit organizations to preserve and publish historical records. Since 1964, the NHPRC has awarded some 4,500 grants; the Office of Government Information Services is a Freedom of Information Act resource for the public and the government. Congress has charged NARA with reviewing FOIA policies and compliance of Federal agencies and to recommend changes to FOIA. NARA's mission includes resolving FOIA disputes between Federal agencies and requesters; each branch and agency of the U. S. government was responsible for maintaining its own documents, which resulted in the loss and destruction of records. Congress established the National Archives Establishment in 1934 to centralize federal record keeping, with the Archivist of the United States as chief administrator; the National Archives was incorporated with GSA in 1949.
The first Archivist, R. D. W. Connor, began serving in 1934; as a result of a first Hoover Commission recommendation, in 1949 the National Archives was placed within the newly formed General Services Administration. The Archivist served as a subordinate official to the GSA Administrator until the National Archives and Records Administration became an independent agency on April 1, 1985. In March 2006, it was revealed by the Archivist of the United States in a public hearing that a memorandum of understanding between NARA and various government agencies existed to "reclassify", i.e. withdraw from public access, certain documents in the name of national security, to do so in a manner such that researchers would not be to discover the process. An audit indicated that more than one third withdrawn since 1999 did not contain sensitive information; the program was scheduled to end in 2007. In 2010, Executive Order 13526 created the National Declassification Center to coordinate declassification practices across agencies, provide secure document services to other agencies, review records in NARA custody for declassification.
NARA's holdings are classed into "record groups" reflecting the governmental department or agency from which they originated. Records include paper documents, still pictures, motion pictures, electronic media. Archival descriptions of the permanent holdings of the federal government in the custody of NARA are stored in the National Archives Catalog; the archival descriptions include information on traditional paper holdings, electronic records, artifacts. As of December 2012, the catalog consisted of about 10 billion logical data records describing 527,000 artifacts and encompassing 81% of NARA's records. There are 922,000 digital copies of digitized materials. Most records at NARA are in the public domain, as works of the federal government are excluded from copyright protection. However, records from other sources may still be protected by donor agreements. Executive Order 13526 directs originating agencies to declassify documents if possible before shipment to NARA for long-term storage, but NARA stores some classified documents until they can be declassified.
Its Information Security Oversight Office monitors and sets policy for the U. S. government's security classification system. Many of NARA's most requested records are used for genealogy research; this includes census records from 1790 to 1940, ships' passenger lists, naturalization records. Archival Recovery Teams investigate the theft of records; the most well known facility of the National Archives and Records Administration is the National Archives Building, located north of the National Mall on Constitution Avenue in Washington, D. C.. A sister facility, known as the National Archives at College Park was opened 1994 near the University of Maryland, College Park; the Washington National Records Center located in the Washington, D. C. metropolitan area, is a large warehouse facility where federal records that are still under the control of the creating agency are stored. Federal government agencies pay a yearly fee for storage at the facility. In accordance with federal records schedules, documents at WNRC are transferred to the legal custody of the National Archives after a certain time.
Temporary records at WNRC are
An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its directional flight controls. Some other aircrew members, such as navigators or flight engineers, are considered aviators, because they are involved in operating the aircraft's navigation and engine systems. Other aircrew members, such as flight attendants and ground crew, are not classified as aviators. In recognition of the pilots' qualifications and responsibilities, most militaries and many airlines worldwide award aviator badges to their pilots; the first recorded use of the term aviator was in 1887, as a variation of "aviation", from the Latin avis, coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne. The term aviatrix, now archaic, was used for a female aviator; these terms were used more in the early days of aviation, when airplanes were rare, connoted bravery and adventure. For example, a 1905 reference work described the Wright brothers' first airplane: "The weight, including the body of the aviator, is a little more than 700 pounds".
To ensure the safety of people in the air and on the ground, early aviation soon required that aircraft be under the operational control of a properly trained, certified pilot at all times, responsible for the safe and legal completion of the flight. The Aéro-Club de France delivered the first certificate to Louis Blériot in 1908—followed by Glenn Curtiss, Léon Delagrange, Robert Esnault-Pelterie; the British Royal Aero Club followed in 1910 and the Aero Club of America in 1911. Civilian pilots fly aircraft of all types for pleasure, charity, or in pursuance of a business, or commercially for non-scheduled and scheduled passenger and cargo air carriers, corporate aviation, forest fire control, law enforcement, etc; when flying for an airline, pilots are referred to as airline pilots, with the pilot in command referred to as the captain. There are 290,000 airline pilots in the world in 2017 and aircraft simulator manufacturer CAE Inc. forecasts a need for 255,000 new ones for a population of 440,000 by 2027, 150,000 for growth and 105,000 to offset retirement and attrition: 90,000 in Asia-Pacific, 85,000 in Americas, 50,000 in Europe and 30,000 in Middle East & Africa.
Boeing expects 790,000 new pilots in 20 years from 2018, 635,000 for commercial aviation, 96,000 for business aviation and 59,000 for helicopters: 33% in Asia Pacific, 26% in North America, 18% in Europe, 8% in the Middle East, 7% in Latin America, 4% in Africa and 3% in Russia/ Central Asia. By November 2017, due a shortage of qualified pilots, some pilots are leaving corporate aviation to return to airlines. In one example a Global 6000 pilot, making $250,000 a year for 10 to 15 flight hours a month, returned to American Airlines with full seniority. A Gulfstream G650 or Global 6000 pilot might earn between $245,000 and $265,000, recruiting one may require up to $300,000. At the other end of the spectrum, constrained by the available pilots, some small carriers hire new pilots who need 300 hours to jump to airlines in a year, they may recruit non-career pilots who have other jobs or airline retirees who want to continue to fly. The number of airline pilots could decrease as automation replaces copilots and pilots as well.
In January 2017 Rhett Ross, CEO of Continental Motors said "my concern is that in the next two decades—if not sooner—automated and autonomous flight will have developed sufficiently to put downward pressure on both wages and the number and kind of flying jobs available. So if a kid asks the question now and he or she is 18, 20 years from now will be 2037 and our would-be careerist will be 38—not mid-career. Who among us thinks aviation and for-hire flying will look like it does now?" Christian Dries, owner of Diamond Aircraft Austria said "Behind the curtain, aircraft manufacturers are working on a single-pilot cockpit where the airplane can be controlled from the ground and only in case of malfunction does the pilot of the plane interfere. The flight will be autonomous and I expect this to happen in the next five to six years for freighters."In August 2017 financial company UBS predicted pilotless airliners are technically feasible and could appear around 2025, offering around $35bn of savings in pilot costs: $26bn for airlines, $3bn for business jets and $2.1bn for civil helicopters.
Regulations have to adapt with air cargo at the forefront, but pilotless flights could be limited by consumer behaviour: 54% of 8,000 people surveyed are defiant while 17% are supportive, with acceptation progressively forecast. AVweb reporter Geoff Rapoport stated, "pilotless aircraft are an appealing prospect for airlines bracing for the need to hire several hundred thousand new pilots in the next decade. Wages and training costs have been rising at regional U. S. airlines over the last several years as the major airlines have hired pilots from the regionals at unprecedented rates to cover increased air travel demand from economic expansion and a wave of retirements". Going to pilotless airliners could be done in one bold step or in gradual improvements like by reducing the cockpit crew for long haul missions or allowing single pilot cargo aircraft; the industry has not decided
Global Positioning System
The Global Positioning System Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Air Force. It is a global navigation satellite system that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. Obstacles such as mountains and buildings block the weak GPS signals; the GPS does not require the user to transmit any data, it operates independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the GPS positioning information. The GPS provides critical positioning capabilities to military and commercial users around the world; the United States government created the system, maintains it, makes it accessible to anyone with a GPS receiver. The GPS project was launched by the U. S. Department of Defense in 1973 for use by the United States military and became operational in 1995.
It was allowed for civilian use in the 1980s. Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS and implement the next generation of GPS Block IIIA satellites and Next Generation Operational Control System. Announcements from Vice President Al Gore and the White House in 1998 initiated these changes. In 2000, the U. S. Congress authorized the modernization effort, GPS III. During the 1990s, GPS quality was degraded by the United States government in a program called "Selective Availability"; the GPS system is provided by the United States government, which can selectively deny access to the system, as happened to the Indian military in 1999 during the Kargil War, or degrade the service at any time. As a result, several countries have developed or are in the process of setting up other global or regional satellite navigation systems; the Russian Global Navigation Satellite System was developed contemporaneously with GPS, but suffered from incomplete coverage of the globe until the mid-2000s.
GLONASS can be added to GPS devices, making more satellites available and enabling positions to be fixed more and to within two meters. China's BeiDou Navigation Satellite System is due to achieve global reach in 2020. There are the European Union Galileo positioning system, India's NAVIC. Japan's Quasi-Zenith Satellite System is a GPS satellite-based augmentation system to enhance GPS's accuracy; when selective availability was lifted in 2000, GPS had about a five-meter accuracy. The latest stage of accuracy enhancement uses the L5 band and is now deployed. GPS receivers released in 2018 that use the L5 band can have much higher accuracy, pinpointing to within 30 centimetres or 11.8 inches. The GPS project was launched in the United States in 1973 to overcome the limitations of previous navigation systems, integrating ideas from several predecessors, including classified engineering design studies from the 1960s; the U. S. Department of Defense developed the system, which used 24 satellites, it was developed for use by the United States military and became operational in 1995.
Civilian use was allowed from the 1980s. Roger L. Easton of the Naval Research Laboratory, Ivan A. Getting of The Aerospace Corporation, Bradford Parkinson of the Applied Physics Laboratory are credited with inventing it; the work of Gladys West is credited as instrumental in the development of computational techniques for detecting satellite positions with the precision needed for GPS. The design of GPS is based on similar ground-based radio-navigation systems, such as LORAN and the Decca Navigator, developed in the early 1940s. Friedwardt Winterberg proposed a test of general relativity – detecting time slowing in a strong gravitational field using accurate atomic clocks placed in orbit inside artificial satellites. Special and general relativity predict that the clocks on the GPS satellites would be seen by the Earth's observers to run 38 microseconds faster per day than the clocks on the Earth; the GPS calculated positions would drift into error, accumulating to 10 kilometers per day. This was corrected for in the design of GPS.
Winterberg, Friedwardt. “Relativistische Zeitdilatation eines künstlichen Satelliten ” When the Soviet Union launched the first artificial satellite in 1957, two American physicists, William Guier and George Weiffenbach, at Johns Hopkins University's Applied Physics Laboratory decided to monitor its radio transmissions. Within hours they realized that, because of the Doppler effect, they could pinpoint where the satellite was along its orbit; the Director of the APL gave them access to their UNIVAC to do the heavy calculations required. Early the next year, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem—pinpointing the user's location, given that of the satellite; this led them and APL to develop the TRANSIT system. In 1959, ARPA played a role in TRANSIT. TRANSIT was first tested in 1960, it used a constellation of five satellites and could provide a navigational fix once per hour. In 1967, the U. S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology required for GPS.
In the 1970s, the ground-based OMEGA navigation system, based on phase comparison of signal transmission from pairs of stations