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102-594: The North American Datum ( NAD ) is the horizontal datum now used to define the geodetic network in North America. A datum is a formal description of the shape of the Earth along with an "anchor" point for the coordinate system. In surveying , cartography , and land-use planning , two North American Datums are in use for making lateral or "horizontal" measurements: the North American Datum of 1927 (NAD 27) and

204-583: A Diamant A rocket launched from the CIEES site at Hammaguir , Algeria . With Astérix, France became the sixth country to have an artificial satellite. Early satellites were built to unique designs. With advancements in technology, multiple satellites began to be built on single model platforms called satellite buses . The first standardized satellite bus design was the HS-333 geosynchronous (GEO) communication satellite launched in 1972. Beginning in 1997, FreeFlyer

306-735: A Lissajous orbit ). Earth observation satellites gather information for reconnaissance , mapping , monitoring the weather , ocean, forest, etc. Space telescopes take advantage of outer space's near perfect vacuum to observe objects with the entire electromagnetic spectrum . Because satellites can see a large portion of the Earth at once, communications satellites can relay information to remote places. The signal delay from satellites and their orbit's predictability are used in satellite navigation systems, such as GPS. Space probes are satellites designed for robotic space exploration outside of Earth, and space stations are in essence crewed satellites. The first artificial satellite launched into

408-414: A catalyst . The most commonly used propellant mixtures on satellites are hydrazine -based monopropellants or monomethylhydrazine – dinitrogen tetroxide bipropellants. Ion thrusters on satellites usually are Hall-effect thrusters , which generate thrust by accelerating positive ions through a negatively-charged grid. Ion propulsion is more efficient propellant-wise than chemical propulsion but its thrust

510-456: A standardized bus to save cost and work, the most popular of which are small CubeSats . Similar satellites can work together as groups, forming constellations . Because of the high launch cost to space, most satellites are designed to be as lightweight and robust as possible. Most communication satellites are radio relay stations in orbit and carry dozens of transponders, each with a bandwidth of tens of megahertz. Satellites are placed from

612-409: A transponder ; it creates a communication channel between a source transmitter and a receiver at different locations on Earth . Communications satellites are used for television , telephone , radio , internet , and military applications. Many communications satellites are in geostationary orbit 22,236 miles (35,785 km) above the equator , so that the satellite appears stationary at

714-576: A Satellite Vehicle", by R. R. Carhart. This expanded on potential scientific uses for satellite vehicles and was followed in June 1955 with "The Scientific Use of an Artificial Satellite", by H. K. Kallmann and W. W. Kellogg. The first artificial satellite was Sputnik 1 , launched by the Soviet Union on 4 October 1957 under the Sputnik program , with Sergei Korolev as chief designer. Sputnik 1 helped to identify

816-448: A U.S. Scout rocket from Wallops Island (Virginia, United States) with an Italian launch team trained by NASA . In similar occasions, almost all further first national satellites were launched by foreign rockets. France was the third country to launch a satellite on its own rocket. On 26 November 1965, the Astérix or A-1 (initially conceptualized as FR.2 or FR-2), was put into orbit by

918-499: A converter between the two systems. The practical impact is that if you use a modern GPS device set to work in NAD ;83 or WGS 84 to navigate to NAD 27 coordinates (as from a topo map) near Seattle , you would be off by about 95 meters (not far enough west), and you'd be about 47 meters off near Miami (not far enough north-northeast), whereas you would be much closer for points near Chicago . The definition of NAD 83(1986)

1020-411: A demand for greater precision. This led to technological innovations such as the 1735 Marine chronometer by John Harrison , but also to a reconsideration of the underlying assumptions about the shape of Earth itself. Isaac Newton postulated that the conservation of momentum should make Earth oblate (wider at the equator), while the early surveys of Jacques Cassini (1720) led him to believe Earth

1122-617: A few hundred meters depending on where in Europe you look. Mars has no oceans and so no sea level, but at least two martian datums have been used to locate places there. In geodetic coordinates , Earth's surface is approximated by an ellipsoid , and locations near the surface are described in terms of geodetic latitude ( ϕ {\displaystyle \phi } ), longitude ( λ {\displaystyle \lambda } ), and ellipsoidal height ( h {\displaystyle h} ). The ellipsoid

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1224-488: A foot or meter at the time could not practically be benchmarked to better than about 0.02 mm. Most USGS topographic maps were published in NAD 27 and many major projects by the United States Army Corps of Engineers and other agencies were defined in NAD 27, so the datum remains important, despite more refined datums being available. Because Earth deviates significantly from a perfect ellipsoid ,

1326-539: A geocentric origin and the Geodetic Reference System 1980 ([[GRS   80]]). "This datum, designated as NAD   83…is based on the adjustment of 250,000 points including 600 satellite Doppler stations which constrain the system to a geocentric origin." NAD   83 may be considered a local referencing system. WGS   84 is the World Geodetic System of 1984. It is the reference frame used by

1428-471: A global reference frame (such as WGS 84 ) is used, the coordinates of a place on the surface generally will change from year to year. Most mapping, such as within a single country, does not span plates. To minimize coordinate changes for that case, a different reference frame can be used, one whose coordinates are fixed to that particular plate. Examples of these reference frames are " NAD 83 " for North America and " ETRS89 " for Europe. Satellite This

1530-404: A global survey is combined with computers, databases, and software able to compensate for local conditions. A point having a given latitude and longitude in NAD 27 may be displaced on the order of many tens of meters from another point having the identical latitude and longitude in NAD 83, so it is important to specify the datum along with the coordinates. The North American Datum of 1927

1632-456: A more accurate representation of some specific area of coverage than WGS   84 can. OSGB36 , for example, is a better approximation to the geoid covering the British Isles than the global WGS   84 ellipsoid. However, as the benefits of a global system outweigh the greater accuracy, the global WGS   84 datum has become widely adopted. The spherical nature of Earth was known by

1734-812: A new geometric reference frame and geopotential datum based on global navigation satellite systems (GNSS), such as the Global Positioning System (GPS), and new gravimetric geoid model, potentially in 2025 or 2026 . The new gravimetric geoid model is the product of the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project. These new reference frames are intended to be easier to access and to maintain than NAD 83 and NAVD 88, which rely on physical survey marks that deteriorate over time. Geodetic datum#Horizontal datum Since

1836-418: A satellite's lifetime. Resource use is difficult to monitor and quantify for satellites and launch vehicles due to their commercially sensitive nature. However, aluminium is a preferred metal in satellite construction due to its lightweight and relative cheapness and typically constitutes around 40% of a satellite's mass. Through mining and refining, aluminium has numerous negative environmental impacts and

1938-602: A series of physically monumented geodetic control points of known location. Global datums, such as WGS 84 and ITRF , are typically bound to the center of mass of the Earth (making them useful for tracking satellite orbits and thus for use in satellite navigation systems. A specific point can have substantially different coordinates, depending on the datum used to make the measurement. For example, coordinates in NAD   83 can differ from NAD   27 by up to several hundred feet. There are hundreds of local horizontal datums around

2040-478: A single global ellipsoid. This is because satellites naturally deal with Earth as a monolithic body. Therefore, the GRS ;80 ellipsoid was developed for best approximating the Earth as a whole, and it became the foundation for the North American Datum of 1983. Though GRS 80 and its close relative, WGS 84 , are generally not the best fit for any given region, a need for the closest fit largely evaporates when

2142-449: A thin cable called a tether . Recovery satellites are satellites that provide a recovery of reconnaissance, biological, space-production and other payloads from orbit to Earth. Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation. Space-based solar power satellites are proposed satellites that would collect energy from sunlight and transmit it for use on Earth or other places. Since

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2244-588: A thought experiment by Isaac Newton to explain the motion of natural satellites , in his Philosophiæ Naturalis Principia Mathematica (1687). The first fictional depiction of a satellite being launched into orbit was a short story by Edward Everett Hale , " The Brick Moon " (1869). The idea surfaced again in Jules Verne 's The Begum's Fortune (1879). In 1903, Konstantin Tsiolkovsky (1857–1935) published Exploring Space Using Jet Propulsion Devices , which

2346-484: A traditional standard horizontal or vertical datum. A standard datum specification (whether horizontal, vertical, or 3D) consists of several parts: a model for Earth's shape and dimensions, such as a reference ellipsoid or a geoid ; an origin at which the ellipsoid/geoid is tied to a known (often monumented) location on or inside Earth (not necessarily at 0 latitude 0 longitude); and multiple control points or reference points that have been precisely measured from

2448-544: Is "the horizontal control datum for the United States that was defined by a location and azimuth on the Clarke spheroid of 1866, with origin at (the survey station) Meades Ranch (Kansas) ." ... The geoidal height at Meades Ranch was assumed to be zero, as sufficient gravity data was not available, and this was needed to relate surface measurements to the datum. "Geodetic positions on the North American Datum of 1927 were derived from

2550-400: Is a commercial off-the-shelf software application for satellite mission analysis, design, and operations. After the late 2010s, and especially after the advent and operational fielding of large satellite internet constellations —where on-orbit active satellites more than doubled over a period of five years—the companies building the constellations began to propose regular planned deorbiting of

2652-499: Is a model used to precisely measure positions on Earth; it is thus a crucial component of any spatial reference system or map projection . A horizontal datum binds a specified reference ellipsoid , a mathematical model of the shape of the earth, to the physical earth. Thus, the geographic coordinate system on that ellipsoid can be used to measure the latitude and longitude of real-world locations. Regional horizontal datums, such as NAD 27 and NAD 83 , usually create this binding with

2754-759: Is a refinement of the NAD 83 datum using data from a network of very accurate GPS receivers at Continuously Operating Reference Stations (CORS). The NAD 83(2011) describes the main North American Plate, while the MA11 and PA11 solutions are for the Mariana Plate and the Pacific Plate respectively. To improve the National Spatial Reference System, NAD 83, along with North American Vertical Datum of 1988 (NAVD 88), are set to be replaced with

2856-474: Is an accepted version of this page A satellite or artificial satellite is an object, typically a spacecraft , placed into orbit around a celestial body . They have a variety of uses, including communication relay, weather forecasting , navigation ( GPS ), broadcasting , scientific research, and Earth observation. Additional military uses are reconnaissance, early warning , signals intelligence and, potentially, weapon delivery. Other satellites include

2958-461: Is based on the GRS 80 spheroid, as was WGS 84, so many older publications indicate no difference. WGS 84 subsequently changed to a slightly less flattened spheroid . This change in flattening is about 0.1 mm, a difference so small that computational programs often do not distinguish between the two ellipsoids. However, due to differences in how the reference ellipsoids are centered and oriented, coordinates in

3060-512: Is completely parameterised by the semi-major axis a {\displaystyle a} and the flattening f {\displaystyle f} . From a {\displaystyle a} and f {\displaystyle f} it is possible to derive the semi-minor axis b {\displaystyle b} , first eccentricity e {\displaystyle e} and second eccentricity e ′ {\displaystyle e'} of

3162-610: Is currently unclear. The visibility of man-made objects in the night sky may also impact people's linkages with the world, nature, and culture. At all points of a satellite's lifetime, its movement and processes are monitored on the ground through a network of facilities. The environmental cost of the infrastructure as well as day-to-day operations is likely to be quite high, but quantification requires further investigation. Particular threats arise from uncontrolled de-orbit. Some notable satellite failures that polluted and dispersed radioactive materials are Kosmos 954 , Kosmos 1402 and

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3264-476: Is defined by the latitude and longitude of an initial point ( Meades Ranch Triangulation Station in Kansas), the direction of a line between this point and a specified second point, and two dimensions that define the spheroid. The North American Datum of 1983 is based on a newer defined spheroid (GRS 80); it is an Earth-centered (or " geocentric ") datum having no initial point or initial direction. NOAA provides

3366-538: Is defined with respect to the average of stations all over the world. Thus the two systems naturally diverge over time. For much of the United States the relative rate is on the order of 1 to 2 cm per year. Hawaii and the coastal portions of central and southern California west of the San Andreas Fault are not on the North American Plate, so their divergence rate differs. The United States National Spatial Reference System NAD 83(2011/MA11/PA11) epoch 2010.00,

3468-399: Is dependent on rocket design and fuel type. The amount of green house gases emitted by rockets is considered trivial as it contributes significantly less, around 0.01%, than the aviation industry yearly which itself accounts for 2-3% of the total global greenhouse gas emissions. Rocket emissions in the stratosphere and their effects are only beginning to be studied and it is likely that

3570-473: Is deployed for military or intelligence purposes, it is known as a spy satellite or reconnaissance satellite. Their uses include early missile warning, nuclear explosion detection, electronic reconnaissance, and optical or radar imaging surveillance. Navigational satellites are satellites that use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between

3672-517: Is most used in archaeology , cartography , environmental monitoring , meteorology , and reconnaissance applications. As of 2021, there are over 950 Earth observation satellites, with the largest number of satellites operated with Planet Labs . Weather satellites monitor clouds , city lights , fires , effects of pollution , auroras , sand and dust storms , snow cover, ice mapping, boundaries of ocean currents , energy flows, etc. Environmental monitoring satellites can detect changes in

3774-581: Is one of the most carbon-intensive metals. Satellite manufacturing also requires rare elements such as lithium , gold , and gallium , some of which have significant environmental consequences linked to their mining and processing and/or are in limited supply. Launch vehicles require larger amounts of raw materials to manufacture and the booster stages are usually dropped into the ocean after fuel exhaustion. They are not normally recovered. Two empty boosters used for Ariane 5 , which were composed mainly of steel, weighed around 38 tons each, to give an idea of

3876-430: Is the chemical propellant used which then releases ammonia , hydrogen and nitrogen as gas into the upper atmosphere. Also, the environment of the outer atmosphere causes the degradation of exterior materials. The atomic oxygen in the upper atmosphere oxidises hydrocarbon-based polymers like Kapton , Teflon and Mylar that are used to insulate and protect the satellite which then emits gasses like CO 2 and CO into

3978-568: Is the only world referencing system in place today. WGS   84 is the default standard datum for coordinates stored in recreational and commercial GPS units. Users of GPS are cautioned that they must always check the datum of the maps they are using. To correctly enter, display, and to store map related map coordinates, the datum of the map must be entered into the GPS map datum field. Examples of map datums are: The Earth's tectonic plates move relative to one another in different directions at speeds on

4080-573: Is then based on its distance and direction from Meades Ranch: If a point was X meters in azimuth Y degrees from Meades Ranch, measured on the Clarke Ellipsoid of 1866, then its latitude and longitude on that ellipsoid were defined and could be calculated. These are the defining dimensions for NAD 27, but Clarke actually defined his 1866 spheroid as a = 20,926,062 British feet, b = 20,855,121 British feet. The conversion to meters uses Clarke's 1865 inch-meter ratio of 39.370432. The length of

4182-425: Is very small (around 0.5 N or 0.1 lb f ), and thus requires a longer burn time. The thrusters usually use xenon because it is inert , can be easily ionized , has a high atomic mass and storable as a high-pressure liquid. Most satellites use solar panels to generate power, and a few in deep space with limited sunlight use radioisotope thermoelectric generators . Slip rings attach solar panels to

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4284-516: The Greenwich Observatory for longitude, from the Equator for latitude, or from the nearest coast for sea level. Astronomical and chronological methods have limited precision and accuracy, especially over long distances. Even GPS requires a predefined framework on which to base its measurements, so WGS   84 essentially functions as a datum, even though it is different in some particulars from

4386-774: The 39th parallel north and the triangulation arc along the 98th meridian west that was near the geographic center of the contiguous United States . The datum declares the Meades Ranch Triangulation Station in Osborne County, Kansas to be 39°13′26.686″ north latitude, 98°32′30.506″ west longitude. NAD 27 is oriented by declaring the azimuth from Meades Ranch to Waldo Station (also in Osborne County, about 4.5 mi (7.2 km) northwest of Waldo, Russell County ) to be 255°28′14.52″ from north. The latitude and longitude of every other point in North America

4488-802: The American Rocket Society , the National Science Foundation , and the International Geophysical Year, the Army and Navy worked on Project Orbiter with two competing programs. The army used the Jupiter C rocket , while the civilian–Navy program used the Vanguard rocket to launch a satellite. Explorer 1 became the United States' first artificial satellite, on 31 January 1958. The information sent back from its radiation detector led to

4590-721: The Anglo-French Survey (1784–1790) , by the end of the 18th century, survey control networks covered France and the United Kingdom . More ambitious undertakings such as the Struve Geodetic Arc across Eastern Europe (1816-1855) and the Great Trigonometrical Survey of India (1802-1871) took much longer, but resulted in more accurate estimations of the shape of the Earth ellipsoid . The first triangulation across

4692-571: The Chinese military shot down an aging weather satellite, followed by the US Navy shooting down a defunct spy satellite in February 2008. On 18 November 2015, after two failed attempts, Russia successfully carried out a flight test of an anti-satellite missile known as Nudol . On 27 March 2019, India shot down a live test satellite at 300 km altitude in 3 minutes, becoming the fourth country to have

4794-607: The Netherlands , Norway , Pakistan , Poland , Russia , Saudi Arabia , South Africa , Spain , Switzerland , Thailand , Turkey , Ukraine , the United Kingdom and the United States , had some satellites in orbit. Japan's space agency (JAXA) and NASA plan to send a wooden satellite prototype called LingoSat into orbit in the summer of 2024. They have been working on this project for few years and sent first wood samples to

4896-465: The Transit 5-BN-3 . When in a controlled manner satellites reach the end of life they are intentionally deorbited or moved to a graveyard orbit further away from Earth in order to reduce space debris . Physical collection or removal is not economical or even currently possible. Moving satellites out to a graveyard orbit is also unsustainable because they remain there for hundreds of years. It will lead to

4998-736: The U.S. Department of Defense (DoD) and is defined by the National Geospatial-Intelligence Agency (NGA) (formerly the Defense Mapping Agency, then the National Imagery and Mapping Agency). WGS   84 is used by the DoD for all its mapping, charting, surveying, and navigation needs, including its GPS "broadcast" and "precise" orbits. WGS   84 was defined in January 1987 using Doppler satellite surveying techniques. It

5100-557: The United States Coast and Geodetic Survey adopted a national horizontal datum called the United States Standard Datum, based on the Clarke Ellipsoid of 1866. It was fitted to data previously collected for regional datums, which by that time had begun to overlap. In 1913, Canada and Mexico adopted that datum, so it was also renamed the North American Datum. As more data were gathered, discrepancies appeared, so

5202-564: The White House announced on 29 July 1955 that the U.S. intended to launch satellites by the spring of 1958. This became known as Project Vanguard . On 31 July, the Soviet Union announced its intention to launch a satellite by the fall of 1957. Sputnik 2 was launched on 3 November 1957 and carried the first living passenger into orbit, a dog named Laika . The dog was sent without possibility of return. In early 1955, after being pressured by

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5304-450: The elevations of Earth features including terrain , bathymetry , water level , and human-made structures. An approximate definition of sea level is the datum WGS 84 , an ellipsoid , whereas a more accurate definition is Earth Gravitational Model 2008 (EGM2008), using at least 2,159 spherical harmonics . Other datums are defined for other areas or at other times; ED50 was defined in 1950 over Europe and differs from WGS   84 by

5406-455: The (coordinates of and an azimuth at Meades Ranch) through a readjustment of the triangulation of the entire network in which Laplace azimuths were introduced, and the Bowie method was used." NAD   27 is a local referencing system covering North America. The North American Datum of 1983 (NAD 83) is "The horizontal control datum for the United States, Canada, Mexico, and Central America, based on

5508-457: The Earth's vegetation , atmospheric trace gas content, sea state, ocean color, and ice fields. By monitoring vegetation changes over time, droughts can be monitored by comparing the current vegetation state to its long term average. Anthropogenic emissions can be monitored by evaluating data of tropospheric NO 2 and SO 2 . A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via

5610-417: The Earth's orbit was the Soviet Union 's Sputnik 1 , on October 4, 1957. As of December 31, 2022, there are 6,718 operational satellites in the Earth's orbit, of which 4,529 belong to the United States (3,996 commercial), 590 belong to China, 174 belong to Russia, and 1,425 belong to other nations. The first published mathematical study of the possibility of an artificial satellite was Newton's cannonball ,

5712-500: The Earth, called remote sensing . Most Earth observation satellites are placed in low Earth orbit for a high data resolution, though some are placed in a geostationary orbit for an uninterrupted coverage. Some satellites are placed in a Sun-synchronous orbit to have consistent lighting and obtain a total view of the Earth. Depending on the satellites' functions, they might have a normal camera , radar , lidar , photometer , or atmospheric instruments. Earth observation satellite's data

5814-546: The Moon and the Sun. Satellites utilize ultra-white reflective coatings to prevent damage from UV radiation. Without orbit and orientation control, satellites in orbit will not be able to communicate with ground stations on the Earth. Chemical thrusters on satellites usually use monopropellant (one-part) or bipropellant (two-parts) that are hypergolic . Hypergolic means able to combust spontaneously when in contact with each other or to

5916-561: The North American Datum of 1983 (NAD 83). Both are geodetic reference systems based on slightly different assumptions and measurements. Vertical measurements, based on distances above or below Mean High Water (MHW), are calculated using the North American Vertical Datum of 1988 (NAVD 88). NAD 83, along with NAVD 88, is set to be replaced with a new GPS - and gravimetric geoid model-based geometric reference frame and geopotential datum, potentially in 2025 . In 1901

6018-547: The United States was not completed until 1899. The U.S. survey resulted in the North American Datum (horizontal) of 1927 (NAD   27) and the Vertical Datum of 1929 (NAVD29), the first standard datums available for public use. This was followed by the release of national and regional datums over the next several decades. Improving measurements, including the use of early satellites , enabled more accurate datums in

6120-462: The ancient Greeks, who also developed the concepts of latitude and longitude, and the first astronomical methods for measuring them. These methods, preserved and further developed by Muslim and Indian astronomers, were sufficient for the global explorations of the 15th and 16th Centuries. However, the scientific advances of the Age of Enlightenment brought a recognition of errors in these measurements, and

6222-455: The atmosphere. Given the current surge in satellites in the sky, soon hundreds of satellites may be clearly visible to the human eye at dark sites. It is estimated that the overall levels of diffuse brightness of the night skies has increased by up to 10% above natural levels. This has the potential to confuse organisms, like insects and night-migrating birds, that use celestial patterns for migration and orientation. The impact this might have

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6324-603: The atmosphere. For example, SpaceX Starlink satellites, the first large satellite internet constellation to exceed 1000 active satellites on orbit in 2020, are designed to be 100% demisable and burn up completely on their atmospheric reentry at the end of their life, or in the event of an early satellite failure. In different periods, many countries, such as Algeria , Argentina , Australia , Austria , Brazil , Canada , Chile , China , Denmark , Egypt , Finland , France , Germany , India , Iran , Israel , Italy , Japan , Kazakhstan , South Korea , Malaysia , Mexico ,

6426-447: The capability to destroy live satellites. The environmental impact of satellites is not currently well understood as they were previously assumed to be benign due to the rarity of satellite launches. However, the exponential increase and projected growth of satellite launches are bringing the issue into consideration. The main issues are resource use and the release of pollutants into the atmosphere which can happen at different stages of

6528-422: The coordinates of a point from one datum system to another. Because the survey networks upon which datums were traditionally based are irregular, and the error in early surveys is not evenly distributed, datum conversion cannot be performed using a simple parametric function. For example, converting from NAD 27 to NAD 83 is performed using NADCON (later improved as HARN), a raster grid covering North America, with

6630-514: The datum used to make the measurement. There are hundreds of locally developed reference datums around the world, usually referenced to some convenient local reference point. Contemporary datums, based on increasingly accurate measurements of the shape of Earth, are intended to cover larger areas. The most common reference Datums in use in North America are NAD   27, NAD   83, and WGS 84 . The North American Datum of 1927 (NAD   27)

6732-438: The datum was recomputed in 1927, using the same spheroid and origin as its predecessor. The North American Datum of 1927 (NAD 27) was based on surveys of the entire continent from a common reference point that was chosen in 1901, because it was as near the center of the contiguous United States as could be calculated: It was based on a triangulation station at the junction of the transcontinental triangulation arc of 1899 on

6834-534: The density of high atmospheric layers through measurement of its orbital change and provided data on radio-signal distribution in the ionosphere . The unanticipated announcement of Sputnik 1's success precipitated the Sputnik crisis in the United States and ignited the so-called Space Race within the Cold War . In the context of activities planned for the International Geophysical Year (1957–1958),

6936-530: The discovery of the Earth's Van Allen radiation belts . The TIROS-1 spacecraft, launched on April 1, 1960, as part of NASA's Television Infrared Observation Satellite (TIROS) program, sent back the first television footage of weather patterns to be taken from space. In June 1961, three and a half years after the launch of Sputnik 1, the United States Space Surveillance Network cataloged 115 Earth-orbiting satellites. While Canada

7038-408: The disparity on the ground between a point having the same horizontal coordinates in two different datums could reach kilometers if the point is far from the origin of one or both datums. This phenomenon is called datum shift or, more generally, datum transformation , as it may involve rotation and scaling, in addition to displacement. Because Earth is an imperfect ellipsoid, local datums can give

7140-484: The earth's climate. After deorbiting 70% of satellites end up in the ocean and are rarely recovered. Using wood as an alternative material has been posited in order to reduce pollution and debris from satellites that reenter the atmosphere. Space debris pose dangers to the spacecraft (including satellites) in or crossing geocentric orbits and have the potential to drive a Kessler syndrome which could potentially curtail humanity from conducting space endeavors in

7242-937: The ellipsoid The two main reference ellipsoids used worldwide are the GRS   80 and the WGS   84. A more comprehensive list of geodetic systems can be found here . The Global Positioning System (GPS) uses the World Geodetic System 1984 (WGS   84) to determine the location of a point near the surface of Earth. The difference in co-ordinates between datums is commonly referred to as datum shift . The datum shift between two particular datums can vary from one place to another within one country or region, and can be anything from zero to hundreds of meters (or several kilometers for some remote islands). The North Pole , South Pole and Equator will be in different positions on different datums, so True North will be slightly different. Different datums use different interpolations for

7344-670: The ellipsoid that best approximates its shape varies region by region across the world. Clarke 1866, and North American Datum of 1927 with it, were surveyed to best suit North America as a whole. Likewise, historically, most regions of the world used ellipsoids measured locally to best suit the vagaries of Earth's shape in their respective locales. While ensuring the most accuracy locally, this practice makes integrating and disseminating information across regions troublesome. As satellite geodesy and remote sensing technology reached high precision and were made available for civilian applications, it became feasible to acquire information referred to

7446-419: The final rocket stages that place satellites in orbit and formerly useful satellites that later become defunct. Except for passive satellites , most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope thermoelectric generators (RTGs). Most satellites also have a method of communication to ground stations , called transponders . Many satellites use

7548-444: The further pollution of space and future issues with space debris. When satellites deorbit much of it is destroyed during re-entry into the atmosphere due to the heat. This introduces more material and pollutants into the atmosphere. There have been concerns expressed about the potential damage to the ozone layer and the possibility of increasing the earth's albedo , reducing warming but also resulting in accidental geoengineering of

7650-490: The ground). Some imaging satellites chose a Sun-synchronous orbit because they can scan the entire globe with similar lighting. As the number of satellites and space debris around Earth increases, the threat of collision has become more severe. A small number of satellites orbit other bodies (such as the Moon , Mars , and the Sun ) or many bodies at once (two for a halo orbit , three for

7752-412: The impact of regulated ozone-depleting substances. Whilst emissions of water vapour are largely deemed as inert, H 2 O is the source gas for HO x and can also contribute to ozone loss through the formation of ice particles. Black carbon particles emitted by rockets can absorb solar radiation in the stratosphere and cause warming in the surrounding air which can then impact the circulatory dynamics of

7854-462: The impacts will be more critical than emissions in the troposphere. The stratosphere includes the ozone layer and pollutants emitted from rockets can contribute to ozone depletion in a number of ways. Radicals such as NO x , HO x , and ClO x deplete stratospheric O 3 through intermolecular reactions and can have huge impacts in trace amounts. However, it is currently understood that launch rates would need to increase by ten times to match

7956-633: The later 20th century, such as NAD 83 in North America, ETRS89 in Europe, and GDA94 in Australia. At this time global datums were also first developed for use in satellite navigation systems, especially the World Geodetic System (WGS   84) used in the U.S. global positioning system (GPS), and the International Terrestrial Reference System and Frame (ITRF) used in the European Galileo system. A horizontal datum

8058-400: The mid-2000s, satellites have been hacked by militant organizations to broadcast propaganda and to pilfer classified information from military communication networks. For testing purposes, satellites in low earth orbit have been destroyed by ballistic missiles launched from the Earth. Russia , United States , China and India have demonstrated the ability to eliminate satellites. In 2007,

8160-705: The most potent scientific tools of the Twentieth Century." The United States had been considering launching orbital satellites since 1945 under the Bureau of Aeronautics of the United States Navy . Project RAND eventually released the report, but considered the satellite to be a tool for science, politics, and propaganda, rather than a potential military weapon. In 1946, American theoretical astrophysicist Lyman Spitzer proposed an orbiting space telescope . In February 1954, Project RAND released "Scientific Uses for

8262-546: The older satellites that reached the end of life , as a part of the regulatory process of obtaining a launch license. The largest artificial satellite ever is the International Space Station . By the early 2000s, and particularly after the advent of CubeSats and increased launches of microsats —frequently launched to the lower altitudes of low Earth orbit (LEO)—satellites began to more frequently be designed to get destroyed, or breakup and burnup entirely in

8364-642: The order of 50 to 100 mm (2.0 to 3.9 in) per year. Therefore, locations on different plates are in motion relative to one another. For example, the longitudinal difference between a point on the equator in Uganda, on the African Plate , and a point on the equator in Ecuador, on the South American Plate , increases by about 0.0014 arcseconds per year. These tectonic movements likewise affect latitude. If

8466-409: The origin and physically monumented. Then the coordinates of other places are measured from the nearest control point through surveying . Because the ellipsoid or geoid differs between datums, along with their origins and orientation in space, the relationship between coordinates referred to one datum and coordinates referred to another datum is undefined and can only be approximated. Using local datums,

8568-532: The possible use of communications satellites for mass communications. He suggested that three geostationary satellites would provide coverage over the entire planet. In May 1946, the United States Air Force 's Project RAND released the Preliminary Design of an Experimental World-Circling Spaceship , which stated "A satellite vehicle with appropriate instrumentation can be expected to be one of

8670-513: The precise shape and size of Earth ( reference ellipsoids ). For example, in Sydney there is a 200 metres (700 feet) difference between GPS coordinates configured in GDA (based on global standard WGS   84) and AGD (used for most local maps), which is an unacceptably large error for some applications, such as surveying or site location for scuba diving . Datum conversion is the process of converting

8772-412: The quantity of materials that are often left in the ocean. Rocket launches release numerous pollutants into every layer of the atmosphere, especially affecting the atmosphere above the tropopause where the byproducts of combustion can reside for extended periods. These pollutants can include black carbon , CO 2 , nitrogen oxides (NO x ), aluminium and water vapour , but the mix of pollutants

8874-461: The rise of the global positioning system (GPS), the ellipsoid and datum WGS 84 it uses has supplanted most others in many applications. The WGS   84 is intended for global use, unlike most earlier datums. Before GPS, there was no precise way to measure the position of a location that was far from reference points used in the realization of local datums, such as from the Prime Meridian at

8976-427: The same point in the sky; therefore the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track the satellite. Others form satellite constellations in low Earth orbit , where antennas on the ground have to follow the position of the satellites and switch between satellites frequently. When an Earth observation satellite or a communications satellite

9078-409: The satellite; the slip rings can rotate to be perpendicular with the sunlight and generate the most power. All satellites with a solar panel must also have batteries , because sunlight is blocked inside the launch vehicle and at night. The most common types of batteries for satellites are lithium-ion , and in the past nickel–hydrogen . Earth observation satellites are designed to monitor and survey

9180-404: The satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few meters in real time. Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects. Tether satellites are satellites that are connected to another satellite by

9282-489: The space in 2021 to test the material's resilience to space conditions. Most satellites use chemical or ion propulsion to adjust or maintain their orbit , coupled with reaction wheels to control their three axis of rotation or attitude. Satellites close to Earth are affected the most by variations in the Earth's magnetic , gravitational field and the Sun's radiation pressure ; satellites that are further away are affected more by other bodies' gravitational field by

9384-458: The special conditions of space could be useful for scientific experiments. The book described geostationary satellites (first put forward by Konstantin Tsiolkovsky ) and discussed the communication between them and the ground using radio, but fell short with the idea of using satellites for mass broadcasting and as telecommunications relays. In a 1945 Wireless World article, English science fiction writer Arthur C. Clarke described in detail

9486-459: The stratosphere. Both warming and changes in circulation can then cause depletion of the ozone layer. Several pollutants are released in the upper atmospheric layers during the orbital lifetime of LEO satellites. Orbital decay is caused by atmospheric drag and to keep the satellite in the correct orbit the platform occasionally needs repositioning. To do this nozzle-based systems use a chemical propellant to create thrust. In most cases hydrazine

9588-409: The surface to the orbit by launch vehicles , high enough to avoid orbital decay by the atmosphere . Satellites can then change or maintain the orbit by propulsion , usually by chemical or ion thrusters . As of 2018, about 90% of the satellites orbiting the Earth are in low Earth orbit or geostationary orbit ; geostationary means the satellites stay still in the sky (relative to a fixed point on

9690-503: The two datums differ from each other by amounts on the order of a meter over much of the United States. Each datum has undergone refinements with more accurate and later measurements. One well-known difference is the placement of the center of the Earth, with the two systems differing by about 2.2 metres (7.2 ft). In addition, NAD 83 is defined to remain constant over time for points on the North American Plate , whereas WGS 84

9792-470: The value of each cell being the average adjustment distance for that area in latitude and longitude. Datum conversion may frequently be accompanied by a change of map projection . A geodetic reference datum is a known and constant surface which is used to describe the location of unknown points on Earth. Since reference datums can have different radii and different center points, a specific point on Earth can have substantially different coordinates depending on

9894-524: The world, usually referenced to some convenient local reference point. Contemporary datums, based on increasingly accurate measurements of the shape of Earth, are intended to cover larger areas. The WGS 84 datum, which is almost identical to the NAD 83 datum used in North America and the ETRS89 datum used in Europe, is a common standard datum. A vertical datum is a reference surface for vertical positions , such as

9996-421: Was prolate (wider at the poles). The subsequent French geodesic missions (1735-1739) to Lapland and Peru corroborated Newton, but also discovered variations in gravity that would eventually lead to the geoid model. A contemporary development was the use of the trigonometric survey to accurately measure distance and location over great distances. Starting with the surveys of Jacques Cassini (1718) and

10098-412: Was redefined again and was more closely aligned with International Earth Rotation Service (IERS) frame ITRF 94. It was then formally called WGS   84 (G873). WGS   84 (G873) was adopted as the reference frame for broadcast orbits on January 29, 1997. Another update brought it to WGS   84 (G1674). The WGS   84 datum, within two meters of the NAD   83 datum used in North America,

10200-426: Was the first academic treatise on the use of rocketry to launch spacecraft. He calculated the orbital speed required for a minimal orbit, and inferred that a multi-stage rocket fueled by liquid propellants could achieve this. Herman Potočnik explored the idea of using orbiting spacecraft for detailed peaceful and military observation of the ground in his 1928 book, The Problem of Space Travel . He described how

10302-419: Was the third country to build a satellite which was launched into space, it was launched aboard an American rocket from an American spaceport. The same goes for Australia, whose launch of the first satellite involved a donated U.S. Redstone rocket and American support staff as well as a joint launch facility with the United Kingdom. The first Italian satellite San Marco 1 was launched on 15 December 1964 on

10404-448: Was used as the reference frame for broadcast GPS Ephemerides (orbits) beginning January 23, 1987. At 0000 GMT January 2, 1994, WGS   84 was upgraded in accuracy using GPS measurements. The formal name then became WGS   84 (G730), since the upgrade date coincided with the start of GPS Week 730. It became the reference frame for broadcast orbits on June 28, 1994. At 0000 GMT September 30, 1996 (the start of GPS Week 873), WGS   84

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