United States Department of Defense
The Department of Defense is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government concerned directly with national security and the United States Armed Forces. The department is the largest employer in the world, with nearly 1.3 million active duty servicemen and women as of 2016. Adding to its employees are over 826,000 National Guardsmen and Reservists from the four services, over 732,000 civilians bringing the total to over 2.8 million employees. Headquartered at the Pentagon in Arlington, just outside Washington, D. C. the DoD's stated mission is to provide "the military forces needed to deter war and ensure our nation's security". The Department of Defense is headed by the Secretary of Defense, a cabinet-level head who reports directly to the President of the United States. Beneath the Department of Defense are three subordinate military departments: the United States Department of the Army, the United States Department of the Navy, the United States Department of the Air Force.
In addition, four national intelligence services are subordinate to the Department of Defense: the Defense Intelligence Agency, the National Security Agency, the National Geospatial-Intelligence Agency, the National Reconnaissance Office. Other Defense Agencies include the Defense Advanced Research Projects Agency, the Defense Logistics Agency, the Missile Defense Agency, the Defense Health Agency, Defense Threat Reduction Agency, the Defense Security Service, the Pentagon Force Protection Agency, all of which are under the command of the Secretary of Defense. Additionally, the Defense Contract Management Agency provides acquisition insight that matters, by delivering actionable acquisition intelligence from factory floor to the warfighter. Military operations are managed by ten functional Unified combatant commands; the Department of Defense operates several joint services schools, including the Eisenhower School and the National War College. The history of the defense of the United States started with the Continental Congress in 1775.
The creation of the United States Army was enacted on 14 June 1775. This coincides with the American holiday Flag Day; the Second Continental Congress would charter the United States Navy, on 13 October 1775, create the United States Marine Corps on 10 November 1775. The Preamble of the United States Constitution gave the authority to the federal government to defend its citizens: We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America. Upon the seating of the first Congress on 4 March 1789, legislation to create a military defense force stagnated as they focused on other concerns relevant to setting up the new government. President George Washington went to Congress to remind them of their duty to establish a military twice during this time.
On the last day of the session, 29 September 1789, Congress created the War Department, historic forerunner of the Department of Defense. The War Department handled naval affairs until Congress created the Navy Department in 1798; the secretaries of each of these departments reported directly to the president as cabinet-level advisors until 1949, when all military departments became subordinate to the Secretary of Defense. After the end of World War II, President Harry Truman proposed creation of a unified department of national defense. In a special message to Congress on 19 December 1945, the President cited both wasteful military spending and inter-departmental conflicts. Deliberations in Congress went on for months focusing on the role of the military in society and the threat of granting too much military power to the executive. On 26 July 1947, Truman signed the National Security Act of 1947, which set up a unified military command known as the "National Military Establishment", as well as creating the Central Intelligence Agency, the National Security Council, National Security Resources Board, United States Air Force and the Joint Chiefs of Staff.
The act placed the National Military Establishment under the control of a single Secretary of Defense. The National Military Establishment formally began operations on 18 September, the day after the Senate confirmed James V. Forrestal as the first Secretary of Defense; the National Military Establishment was renamed the "Department of Defense" on 10 August 1949 and absorbed the three cabinet-level military departments, in an amendment to the original 1947 law. Under the Department of Defense Reorganization Act of 1958, channels of authority within the department were streamlined, while still maintaining the ordinary authority of the Military Departments to organize and equip their associated forces; the Act clarified the overall decision-making authority of the Secretary of Defense with respect to these subordinate Military Departments and more defined the operational chain of command over U. S. military forces as running from the president to the Secretary of Defense and to the unified combatant commanders.
Provided in this legislation was a centralized research authority, the Advanced Research Projects Agency known as DARPA. The act was written and promoted by the Eisenhower administration, was signed into law 6 August 1958; the Secretary of Defense, appointed by the president with the advice and consent of the Senate, is by federal law (1
Seismometer
A seismometer is an instrument that responds to ground motions, such as caused by earthquakes, volcanic eruptions, explosions. Seismometers are combined with a timing device and a recording device to form a seismograph; the output of such a device — recorded on paper or film, now recorded and processed digitally — is a seismogram. Such data is used to locate and characterize earthquakes, to study the earth's internal structure. A simple seismometer, sensitive to up-down motions of the Earth, is like a weight hanging from a spring, both suspended from a frame that moves along with any motion detected; the relative motion between the weight and the frame provides a measurement of the vertical ground motion. A rotating drum is attached to the frame and a pen is attached to the weight, thus recording any ground motion in a seismogram. Any movement of the ground moves the frame; the mass tends not to move because of its inertia, by measuring the movement between the frame and the mass, the motion of the ground can be determined.
Early seismometers used optical levers or mechanical linkages to amplify the small motions involved, recording on soot-covered paper or photographic paper. Modern instruments use electronics. In some systems, the mass is held nearly motionless relative to the frame by an electronic negative feedback loop; the motion of the mass relative to the frame is measured, the feedback loop applies a magnetic or electrostatic force to keep the mass nearly motionless. The voltage needed to produce this force is the output of the seismometer, recorded digitally. In other systems the weight is allowed to move, its motion produces an electrical charge in a coil attached to the mass which voltage moves through the magnetic field of a magnet attached to the frame; this design is used in a geophone, used in exploration for oil and gas. Seismic observatories have instruments measuring three axes: north-south, east-west, vertical. If only one axis is measured, it is the vertical because it is less noisy and gives better records of some seismic waves.
The foundation of a seismic station is critical. A professional station is sometimes mounted on bedrock; the best mountings may be in deep boreholes, which avoid thermal effects, ground noise and tilting from weather and tides. Other instruments are mounted in insulated enclosures on small buried piers of unreinforced concrete. Reinforcing rods and aggregates would distort the pier as the temperature changes. A site is always surveyed for ground noise with a temporary installation before pouring the pier and laying conduit. European seismographs were placed in a particular area after a destructive earthquake. Today, they are concentrated in high-risk regions; the word derives from the Greek σεισμός, seismós, a shaking or quake, from the verb σείω, seíō, to shake. Seismograph is another Greek term from γράφω, gráphō, to draw, it is used to mean seismometer, though it is more applicable to the older instruments in which the measuring and recording of ground motion were combined, than to modern systems, in which these functions are separated.
Both types provide a continuous record of ground motion. The technical discipline concerning such devices is called seismometry, a branch of seismology; the concept of measuring the "shaking" of something means that the word "seismograph" might be used in a more general sense. For example, a monitoring station that tracks changes in electromagnetic noise affecting amateur radio waves presents an rf seismograph, and Helioseismology studies the "quakes" on the Sun. The first seismometer was made in China during the 2nd Century; the first Western description of the device comes from the French physicist and priest Jean de Hautefeuille in 1703. The modern seismometer was developed in the 19th century. In December 2018, a seismometer was deployed on the planet Mars by the InSight lander, the first time a seismometer was placed onto the surface of another planet. In AD 132, Zhang Heng of China's Han dynasty invented the first seismoscope, called Houfeng Didong Yi; the description we have, from the History of the Later Han Dynasty, says that it was a large bronze vessel, about 2 meters in diameter.
When there was an earthquake, one of the dragons' mouths would open and drop its ball into a bronze toad at the base, making a sound and showing the direction of the earthquake. On at least one occasion at the time of a large earthquake in Gansu in AD 143, the seismoscope indicated an earthquake though one was not felt; the available text says that inside the vessel was a central column that could move along eight tracks. The first earthquake recorded by this seismoscope was "somewhere in the east". Days a rider from the east reported this earthquake. By the 13th century, seismographic devices existed in the Maragheh observatory in Persia. French physicist and priest Jean de Hautefeuille built one in 1703. After 1880, most seismometers were descend
Computer
A computer is a device that can be instructed to carry out sequences of arithmetic or logical operations automatically via computer programming. Modern computers have the ability to follow generalized sets of called programs; these programs enable computers to perform an wide range of tasks. A "complete" computer including the hardware, the operating system, peripheral equipment required and used for "full" operation can be referred to as a computer system; this term may as well be used for a group of computers that are connected and work together, in particular a computer network or computer cluster. Computers are used as control systems for a wide variety of industrial and consumer devices; this includes simple special purpose devices like microwave ovens and remote controls, factory devices such as industrial robots and computer-aided design, general purpose devices like personal computers and mobile devices such as smartphones. The Internet is run on computers and it connects hundreds of millions of other computers and their users.
Early computers were only conceived as calculating devices. Since ancient times, simple manual devices like the abacus aided people in doing calculations. Early in the Industrial Revolution, some mechanical devices were built to automate long tedious tasks, such as guiding patterns for looms. More sophisticated electrical machines did specialized analog calculations in the early 20th century; the first digital electronic calculating machines were developed during World War II. The speed and versatility of computers have been increasing ever since then. Conventionally, a modern computer consists of at least one processing element a central processing unit, some form of memory; the processing element carries out arithmetic and logical operations, a sequencing and control unit can change the order of operations in response to stored information. Peripheral devices include input devices, output devices, input/output devices that perform both functions. Peripheral devices allow information to be retrieved from an external source and they enable the result of operations to be saved and retrieved.
According to the Oxford English Dictionary, the first known use of the word "computer" was in 1613 in a book called The Yong Mans Gleanings by English writer Richard Braithwait: "I haue read the truest computer of Times, the best Arithmetician that euer breathed, he reduceth thy dayes into a short number." This usage of the term referred to a human computer, a person who carried out calculations or computations. The word continued with the same meaning until the middle of the 20th century. During the latter part of this period women were hired as computers because they could be paid less than their male counterparts. By 1943, most human computers were women. From the end of the 19th century the word began to take on its more familiar meaning, a machine that carries out computations; the Online Etymology Dictionary gives the first attested use of "computer" in the 1640s, meaning "one who calculates". The Online Etymology Dictionary states that the use of the term to mean "'calculating machine' is from 1897."
The Online Etymology Dictionary indicates that the "modern use" of the term, to mean "programmable digital electronic computer" dates from "1945 under this name. Devices have been used to aid computation for thousands of years using one-to-one correspondence with fingers; the earliest counting device was a form of tally stick. Record keeping aids throughout the Fertile Crescent included calculi which represented counts of items livestock or grains, sealed in hollow unbaked clay containers; the use of counting rods is one example. The abacus was used for arithmetic tasks; the Roman abacus was developed from devices used in Babylonia as early as 2400 BC. Since many other forms of reckoning boards or tables have been invented. In a medieval European counting house, a checkered cloth would be placed on a table, markers moved around on it according to certain rules, as an aid to calculating sums of money; the Antikythera mechanism is believed to be the earliest mechanical analog "computer", according to Derek J. de Solla Price.
It was designed to calculate astronomical positions. It was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, has been dated to c. 100 BC. Devices of a level of complexity comparable to that of the Antikythera mechanism would not reappear until a thousand years later. Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use; the planisphere was a star chart invented by Abū Rayhān al-Bīrūnī in the early 11th century. The astrolabe was invented in the Hellenistic world in either the 1st or 2nd centuries BC and is attributed to Hipparchus. A combination of the planisphere and dioptra, the astrolabe was an analog computer capable of working out several different kinds of problems in spherical astronomy. An astrolabe incorporating a mechanical calendar computer and gear-wheels was invented by Abi Bakr of Isfahan, Persia in 1235. Abū Rayhān al-Bīrūnī invented the first mechanical geared lunisolar calendar astrolabe, an early fixed-wired knowledge processing machine with a gear train and gear-wheels, c. 1000 AD.
The sector, a calculating instrument used for solving problems in proportion, trigonometry and division, for various functions, such as squares and cube roots, was developed in
Jet Propulsion Laboratory
The Jet Propulsion Laboratory is a federally funded research and development center and NASA field center in La Cañada Flintridge, United States, though it is referred to as residing in Pasadena, because it has a Pasadena ZIP Code. Founded in the 1930s, the JPL is owned by NASA and managed by the nearby California Institute of Technology for NASA; the laboratory's primary function is the construction and operation of planetary robotic spacecraft, though it conducts Earth-orbit and astronomy missions. It is responsible for operating NASA's Deep Space Network. Among the laboratory's major active projects are the Mars Science Laboratory mission, the Mars Reconnaissance Orbiter, the Juno spacecraft orbiting Jupiter, the NuSTAR X-ray telescope, the SMAP satellite for earth surface soil moisture monitoring, the Spitzer Space Telescope, it is responsible for managing the JPL Small-Body Database, provides physical data and lists of publications for all known small Solar System bodies. The JPL's Space Flight Operations Facility and Twenty-Five-Foot Space Simulator are designated National Historic Landmarks.
JPL traces its beginnings to 1936 in the Guggenheim Aeronautical Laboratory at the California Institute of Technology when the first set of rocket experiments were carried out in the Arroyo Seco. Caltech graduate students Frank Malina, Qian Xuesen, Weld Arnold, Apollo M. O. Smith, along with Jack Parsons and Edward S. Forman, tested a small, alcohol-fueled motor to gather data for Malina's graduate thesis. Malina's thesis advisor was engineer/aerodynamicist Theodore von Kármán, who arranged for U. S. Army financial support for this "GALCIT Rocket Project" in 1939. In 1941, Parsons, Martin Summerfield, pilot Homer Bushey demonstrated the first jet-assisted takeoff rockets to the Army. In 1943, von Kármán, Malina and Forman established the Aerojet Corporation to manufacture JATO rockets; the project took on the name Jet Propulsion Laboratory in November 1943, formally becoming an Army facility operated under contract by the university. During JPL's Army years, the laboratory developed two deployed weapon systems, the MGM-5 Corporal and MGM-29 Sergeant intermediate-range ballistic missiles.
These missiles were the first US ballistic missiles developed at JPL. It developed a number of other weapons system prototypes, such as the Loki anti-aircraft missile system, the forerunner of the Aerobee sounding rocket. At various times, it carried out rocket testing at the White Sands Proving Ground, Edwards Air Force Base, Goldstone, California. In 1954, JPL teamed up with Wernher von Braun's engineers at the Army Ballistic Missile Agency's Redstone Arsenal in Huntsville, Alabama, to propose orbiting a satellite during the International Geophysical Year; the team lost that proposal to Project Vanguard, instead embarked on a classified project to demonstrate ablative re-entry technology using a Jupiter-C rocket. They carried out three successful sub-orbital flights in 1956 and 1957. Using a spare Juno I, the two organizations launched the United States' first satellite, Explorer 1, on January 31, 1958. JPL was transferred to NASA in December 1958, becoming the agency's primary planetary spacecraft center.
JPL engineers designed and operated Ranger and Surveyor missions to the Moon that prepared the way for Apollo. JPL led the way in interplanetary exploration with the Mariner missions to Venus and Mercury. In 1998, JPL opened the Near-Earth Object Program Office for NASA; as of 2013, it has found 95% of asteroids that are a kilometer or more in diameter that cross Earth's orbit. JPL was early to employ female mathematicians. In the 1940s and 1950s, using mechanical calculators, women in an all-female computations group performed trajectory calculations. In 1961, JPL hired Dana Ulery as the first female engineer to work alongside male engineers as part of the Ranger and Mariner mission tracking teams. JPL has been recognized four times by the Space Foundation: with the Douglas S. Morrow Public Outreach Award, given annually to an individual or organization that has made significant contributions to public awareness of space programs, in 1998; when it was founded, JPL's site was west of a rocky flood-plain – the Arroyo Seco riverbed – above the Devil's Gate dam in the northwestern panhandle of the city of Pasadena.
While the first few buildings were constructed in land bought from the city of Pasadena, subsequent buildings were constructed in neighboring unincorporated land that became part of La Cañada Flintridge. Nowadays, most of the 177 acres of the U. S. federal government-owned NASA property that makes up the JPL campus is located in La Cañada Flintridge. Despite this, JPL still uses a Pasadena address as its official mailing address; the city of La Cañada Flintridge was incorporated in 1976, well after JPL attained international recognition as a Pasadena institution. There has been occasional rivalry between the two cities over the issue of which one should be mentioned in the media as the home of the laboratory. There are 6,000 full-time Caltech employees, a few thousand additional contractors working on any given day. NASA has a resident office at the facility staffed by federal managers who oversee JPL's activities and work for NASA. There are some Caltech graduate students, college student interns and co-op students.
The JPL Education Office serves educators and students by providi
Atlas-Agena
The Atlas-Agena was an American expendable launch system derived from the SM-65 Atlas missile. It was a member of the Atlas family of rockets, was launched 109 times between 1960 and 1978, it was used to launch the first five Mariner unmanned probes to the planets Venus and Mars, the Ranger and Lunar Orbiter unmanned probes to the Moon. The upper stage was used as an unmanned orbital target vehicle for the Gemini manned spacecraft to practice rendezvous and docking. However, the launch vehicle family was developed for the Air Force and most of its launches were classified DoD payloads; the Atlas-Agena was a two-and-a-half-stage rocket, with a stage-and-a-half Atlas missile as the first stage, an RM-81 Agena second stage. Atlas D missiles, redesignated as the LV-3, were used as the first stage; these were replaced by the standardized Atlas SLV-3, its derivatives, the SLV-3A and B. The final Atlas-Agena launch used an Atlas E/F; the earliest Agena variant was the Agena A in 1959-60. Most of these were flown on Thor-Agena boosters for the Discoverer program and only four used Atlases, two of which failed.
Late in 1960, Lockheed introduced the uprated Agena B stage, restartable and had longer propellant tanks for more burn time. It first flew on the Thor and did not make its maiden voyage on an Atlas for months, when Midas 3 launched on July 12, 1961. Atlas-Agenas were used for DoD and NASA programs, but proved a reliability nightmare as one failure after another happened. In late 1962, after Ranger 5 suffered another booster malfunction, NASA convened a review board which undertook a wholesale reevaluation of the Atlas-Agena as a launch vehicle; the board found that quality control and checkout procedures were poor, that this situation was exacerbated by the several dozen configurations of the booster, as each individual DoD and NASA program necessitated custom modifications to the Atlas and Agena, the latter differed in its Atlas and Thor variants. The board recommended improved quality control, better hardware, establishing one standardized launch vehicle for all space programs; the end result was the Atlas SLV-3 and Agena D, standardized versions of the Atlas D core and Agena B which would be the same on every launch.
The Agena D first flew in July 1963 for DoD launches, but NASA continued using Agena Bs for the remaining Ranger missions. The Atlas SLV-3 meanwhile first flew in August 1964. Dozens of Atlas SLV-3/Agena D boosters were flown over the following years for the KH-7 Gambit program for a few NASA missions; the last Atlas-Agena was flown in 1978 to launch SEASAT, but on a repurposed Atlas F missile rather than the SLV-3. Launches were conducted from Launch Complexes 12, 13 and 14 at the Cape Canaveral Air Force Station, Launch Complexes 1 and 2 at Point Arguello. All Atlas-Agena vehicles contained an Inadvertent Separation Destruct System to destroy the Agena in the event that it separated prematurely from the Atlas, a situation that could be caused by a booster hard-over or if the Atlas self-destructed in flight; the ISDS charges were mounted on the adapter section between the two vehicles and would activate if a series of tripwires were broken. During the coasting period between staging, the ISDS charges were disabled.
The Atlas's own RSO charges were wired so that they would destroy both vehicles if activated. Most Agenas had their own separate RSO charges, although NASA planetary probes omitted them for weight-saving reasons and due to the flight trajectory used, which meant that destruct of the Agena was no longer possible following staging. Two Atlas-Agena flights involved an intentional destruct of the Atlas while two others resulted in an ISDS destruction of the Agena following in-flight malfunction and self-destruct of the Atlas; the Gemini-Agena Target Vehicle had a specially modified Range Safety destruct system designed to fire slugs into the propellant tanks rather than the conventional method of rupturing them externally, since an inadvertent activation of the RSO system in orbit could endanger the Gemini astronauts. The first Atlas-Agena flight, Midas 1 in February 1960, failed when the unproven ISDS system mistakenly activated at staging, rupturing the Atlas's LOX tank and causing the breakup of the Agena.
The ISDS system was redesigned afterwards and this failure mode did not repeat itself. The Ranger spacecraft were designed to impact the Moon, returning photographs of the lunar surface until their destruction; the spacecraft was designed in three Blocks, all similar in appearance with a forward antenna and magnetometer, supported by a boom, with more sensors and two solar panels and a dish antenna mounted at the base. The first two Block I spacecraft, Ranger 1 and Ranger 2, were launched on August 23 and November 18, 1961, not to the Moon, but in intended high Earth orbits to test the Atlas-Agena and spacecraft capabilities. However, the Agena malfunctioned on both flights and left the probes trapped in a useless low Earth orbit from which they soon decayed; the Block II missions, Ranger 3, Ranger 4, Ranger 5, were launched away from Earth in January and October 1962, but all three failed due to either malfunctions of the probe or launch vehicle difficulties. Ranger 3 missed the Moon entirely.
Ranger 4's solar panels failed to deploy, the navigation system failed, sending the probe to impact the lunar far side without returning any pictures or data. Ranger 5 suffered an unk
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
Telemetry
Telemetry is an automated communications process by which measurements and other data are collected at remote or inaccessible points and transmitted to receiving equipment for monitoring. The word is derived from Greek roots: tele = remote, metron = measure. Systems that need external instructions and data to operate require the counterpart of telemetry, telecommand. Although the term refers to wireless data transfer mechanisms, it encompasses data transferred over other media such as a telephone or computer network, optical link or other wired communications like power line carriers. Many modern telemetry systems take advantage of the low cost and ubiquity of GSM networks by using SMS to receive and transmit telemetry data. A telemeter is a device used to remotely measure any quantity, it consists of a sensor, a transmission path, a display, recording, or control device. Telemeters are the physical devices used in telemetry. Electronic devices are used in telemetry and can be wireless or hard-wired, analog or digital.
Other technologies are possible, such as mechanical and optical. Telemetry may be commutated to allow. Telemetering information over wire had its origins in the 19th century. One of the first data-transmission circuits was developed in 1845 between the Russian Tsar's Winter Palace and army headquarters. In 1874, French engineers built a system of weather and snow-depth sensors on Mont Blanc that transmitted real-time information to Paris. In 1901 the American inventor C. Michalke patented the selsyn, a circuit for sending synchronized rotation information over a distance. In 1906 a set of seismic stations were built with telemetering to the Pulkovo Observatory in Russia. In 1912, Commonwealth Edison developed a system of telemetry to monitor electrical loads on its power grid; the Panama Canal used extensive telemetry systems to monitor locks and water levels. Wireless telemetry made early appearances in the radiosonde, developed concurrently in 1930 by Robert Bureau in France and Pavel Molchanov in Russia.
Molchanov's system modulated temperature and pressure measurements by converting them to wireless Morse code. The German V-2 rocket used a system of primitive multiplexed radio signals called "Messina" to report four rocket parameters, but it was so unreliable that Wernher von Braun once claimed it was more useful to watch the rocket through binoculars. In the US and the USSR, the Messina system was replaced with better systems. Early Soviet missile and space telemetry systems which were developed in the late 1940s used either pulse-position modulation or pulse-duration modulation. In the United States, early work employed similar systems, but were replaced by pulse-code modulation. Soviet interplanetary probes used redundant radio systems, transmitting telemetry by PCM on a decimeter band and PPM on a centimeter band. Telemetry has been used by weather balloons for transmitting meteorological data since 1920. Telemetry is used to transmit drilling mechanics and formation evaluation information uphole, in real time, as a well is drilled.
These services are known as Measurement while Logging while drilling. Information acquired thousands of feet below ground, while drilling, is sent through the drilling hole to the surface sensors and the demodulation software; the pressure wave is translated into useful information after noise filters. This information is used for Formation evaluation, Drilling Optimization, Geosteering. Telemetry is a key factor in modern motor racing, allowing race engineers to interpret data collected during a test or race and use it to properly tune the car for optimum performance. Systems used in series such as Formula One have become advanced to the point where the potential lap time of the car can be calculated, this time is what the driver is expected to meet. Examples of measurements on a race car include accelerations in three axes, temperature readings, wheel speed, suspension displacement. In Formula One, driver input is recorded so the team can assess driver performance and the FIA can determine or rule out driver error as a possible cause.
Developments include two-way telemetry which allows engineers to update calibrations on the car in real time. In Formula One, two-way telemetry surfaced in the early 1990s and consisted of a message display on the dashboard which the team could update, its development continued until May 2001. By 2002, teams were able to change engine mapping and deactivate engine sensors from the pit while the car was on the track. For the 2003 season, the FIA banned two-way telemetry from Formula One. Telemetry has been applied in yacht racing on Oracle Racing's USA 76. One way telemetry system has been applied in R/C racing car to get information by car's sensors like: engine RPM, temperatures, throttle. In the transportation industry, telemetry provides meaningful information about a vehicle or driver's performance by collecting data from sensors within the vehicle; this is undertaken for various reasons ranging from staff compliance monitoring, insurance rating to predictive maintenance. Telemetry is used to link traffic counter devices to data recorders to measure traffic flows and vehicle lengths and weights.
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