The term space debris referred to the natural debris found in the solar system: asteroids and meteoroids. However, with the 1979 beginning of the NASA Orbital Debris Program, the term refers to the debris from the mass of defunct, artificially created objects in space Earth orbit; these include old satellites and spent rocket stages, as well as the fragments from their disintegration and collisions. As of December 2016, five satellite collisions have generated space debris. Space debris is known as orbital debris, space junk, space waste, space trash, space litter or space garbage; as of 5 July 2016, the United States Strategic Command tracked a total of 17,852 artificial objects in orbit above the Earth, including 1,419 operational satellites. However, these are just objects large enough to be tracked; as of January 2019, more than 128 million bits of debris smaller than 1 cm, about 900,000 pieces of debris 1–10 cm, around 34,000 of pieces larger than 10 cm were estimated to be in orbit around the Earth.
Collisions with debris have become a hazard to spacecraft. Below 2,000 km Earth-altitude, pieces of debris are denser than meteoroids. For comparison, the International Space Station orbits in the 300–400 kilometres range, the 2009 satellite collision and 2007 antisat test occurred at 800 to 900 kilometres altitude; the ISS has Whipple shielding. The Kessler syndrome, a runaway chain reaction of collisions exponentially increasing the amount of debris, has been hypothesized to ensue beyond a critical density; this could affect useful polar-orbiting bands, increases the cost of protection for spacecraft missions and could destroy live satellites. Whether Kessler syndrome is underway has been debated; the measurement and potential removal of debris are conducted by some participants in the space industry. There are estimated to be over 128 million pieces of debris smaller than 1 cm as of January 2019. There are 900,000 pieces from one to ten cm; the current count of large debris is 34,000. The technical measurement cutoff is c. 3 mm.
Over 98 percent of the 1,900 tons of debris in low Earth orbit was accounted for by about 1,500 objects, each over 100 kg. Total mass is constant despite addition of many smaller objects, since they reenter the atmosphere sooner. Using a 2008 figure of 8,500 known items, it is estimated at 5,500 t. In LEO there are few "universal orbits"; the closest are sun-synchronous orbits that keep a constant angle between the Sun and the orbital plane. LEO satellites orbit in many planes, up to 15 times a day, causing frequent approaches between objects. Orbits are further changed by perturbations, collisions can occur from any direction. For these reasons, the Kessler syndrome applies to the LEO region; these can lead to a cascade effect. A large-enough collision could make low Earth orbit impassable. Manned missions are at 400 km and below, where air drag helps clear zones of fragments. Atmospheric expansion as a result of space weather raises the critical altitude by increasing drag. Another was fewer launches by Russia.
At higher altitudes, where air drag is less significant, orbital decay takes longer. Slight atmospheric drag, lunar perturbations, Earth's gravity perturbations, solar wind and solar radiation pressure can bring debris down to lower altitudes, but at high altitudes this may take millennia. Although high-altitude orbits are less used than LEO and the onset of the problem is slower, the numbers progress toward the critical threshold more quickly. Many communications satellites are in geostationary orbits, clustering over specific targets and sharing the same orbital path. Although velocities are low between GEO objects, when a satellite becomes derelict it assumes a geosynchronous orbit. Impact velocity peaks at about 1.5 km/s. Orbital perturbations cause longitude drift of the inoperable spacecraft and precession of the orbital plane. Close approaches are estimated at one per year; the collision debris pose less short-term risk than from an LEO collision, but the satellite would become inoperable.
Large objects, such as solar-power satellites, are vulnerable to collisions. Although the ITU now requires proof a satellite can be moved out of its orbital slot at the end of its lifespan, studies suggest this is insufficient. Since GEO orbit is too distant to measure objects under
In astronomy, perturbation is the complex motion of a massive body subject to forces other than the gravitational attraction of a single other massive body. The other forces can include a third body, resistance, as from an atmosphere, the off-center attraction of an oblate or otherwise misshapen body; the study of perturbations began with the first attempts to predict planetary motions in the sky. In ancient times the causes were a mystery. Newton, at the time he formulated his laws of motion and of gravitation, applied them to the first analysis of perturbations, recognizing the complex difficulties of their calculation. Many of the great mathematicians since have given attention to the various problems involved; the complex motions of gravitational perturbations can be broken down. The hypothetical motion that the body follows under the gravitational effect of one other body only is a conic section, can be described with the methods of geometry; this is called an unperturbed Keplerian orbit.
The differences between that and the actual motion of the body are perturbations due to the additional gravitational effects of the remaining body or bodies. If there is only one other significant body the perturbed motion is a three-body problem. A general analytical solution exists for the two-body problem; the two-body problem becomes insoluble if one of the bodies is irregular in shape. Most systems that involve multiple gravitational attractions present one primary body, dominant in its effects; the gravitational effects of the other bodies can be treated as perturbations of the hypothetical unperturbed motion of the planet or satellite around its primary body. In methods of general perturbations, general differential equations, either of motion or of change in the orbital elements, are solved analytically by series expansions; the result is expressed in terms of algebraic and trigonometric functions of the orbital elements of the body in question and the perturbing bodies. This can be applied to many different sets of conditions, is not specific to any particular set of gravitating objects.
General perturbations were investigated first. The classical methods are known as variation of the elements, variation of parameters or variation of the constants of integration. In these methods, it is considered that the body is always moving in a conic section, however the conic section is changing due to the perturbations. If all perturbations were to cease at any particular instant, the body would continue in this conic section indefinitely. General perturbations takes advantage of the fact that in many problems of celestial mechanics, the two-body orbit changes rather due to the perturbations. General perturbations is applicable only if the perturbing forces are about one order of magnitude smaller, or less, than the gravitational force of the primary body. In the Solar System, this is the case. General perturbation methods are preferred for some types of problems, as the source of certain observed motions are found; this is not so for special perturbations. In methods of special perturbations, numerical datasets, representing values for the positions and accelerative forces on the bodies of interest, are made the basis of numerical integration of the differential equations of motion.
In effect, the positions and velocities are perturbed directly, no attempt is made to calculate the curves of the orbits or the orbital elements. Special perturbations can be applied to any problem in celestial mechanics, as it is not limited to cases where the perturbing forces are small. Once applied only to comets and minor planets, special perturbation methods are now the basis of the most accurate machine-generated planetary ephemerides of the great astronomical almanacs. Special perturbations are used for modeling an orbit with computers. Cowell's formulation is the simplest of the special perturbation methods. In a system of n mutually interacting bodies, this method mathematically solves for the Newtonian forces on body i by summing the individual interactions from the other j bodies: r ¨ i = ∑ j = 1 j ≠ i n G m j r i j
A Molniya orbit is a type of satellite orbit designed to provide coverage over high latitudes. It is a elliptical orbit with an inclination of 63.4 degrees, an argument of perigee of 270 degrees and an orbital period of half a sidereal day. The name comes from a series of Soviet/Russian Molniya communications satellites which have used this type of orbit since the mid 1960s; the Molniya orbit has a long dwell time over the hemisphere of interest, while moving quickly over the other. The orbit's high inclination provides a high angle of view to communications and monitoring satellites covering high latitudes. Geostationary orbits, which are inclined over the equator, can only view these regions from a low angle, are unable to view latitudes above 81 degrees; the Molniya orbit was invented by Soviet scientists in the 1960s as a high-latitude communications alternative to geostationary orbits, which require large launch energies to achieve a high perigee and to change inclination to orbit over the equator.
As a result, OKB-1 sought a less energy-demanding orbit. Studies found that this could be achieved using a elliptical orbit with an apogee over Russian territory; the orbit's name refers to the "lightning" speed with which the satellite passes through the perigee. The first use of the Molniya orbit was by the communications satellite series of the same name. After two launch failures in 1964, the first successful satellite to use this orbit, Molniya 1-01, launched on April 23, 1965; the early Molniya-1 satellites were used for long-range military communications, but they were fitted with cameras used for weather monitoring, for assessing clear areas for Zenit spy satellites. The original Molniya satellites had a lifespan of 1.5 years, as their orbits were disrupted by perturbations, they had to be replaced. The succeeding series, the Molniya-2, provided both military and civilian broadcasting and was used to create the Orbita television network, spanning the Soviet Union; these were in turn replaced by the Molniya-3 design, followed by the Mayak and Meridian satellites in 1997 and 2002 respectively.
The Russian US-K early-warning satellites, which watch for American rocket launches, were launched in Molniya orbits from 1967, as part of the Oko system. From 1971, the American Jumpseat and Trumpet satellites were launched into Molniya orbits. Detailed information about both projects remains classified as of 2018; this was followed by the American SDS constellation, which operates with a mix of Molniya and geostationary orbits. These satellites are used to relay imagery from lower flying satellites back to ground stations in the United States and have been active in some capacity since 1976. A single classified communication satellite launch in 1998 may be related to this constellation. A Russian satellite constellation called Nord was designed to support mobile communications at high latitudes, in a manner similar to the Iridium constellation, but it did not progress past the planning phase. Much of the area of the former Soviet Union, Russia in particular, is located at high northern latitudes.
To broadcast to these latitudes from a geostationary orbit requires considerable power due to the low elevation angles, the extra distance and atmospheric attenuation that comes with it. As a rule of thumb, elevation angles of less than 10° can cause problems, depending on the communications frequency. A satellite in a Molniya orbit is better suited to communications in these regions, because it looks more directly down on them during large portions of its orbit. With an apogee altitude as high as 40,000 kilometres and an apogee sub-satellite point of 63.4 degrees north, it spends a considerable portion of its orbit with excellent visibility in the northern hemisphere, from Russia as well as from northern Europe and Canada. While Molniya orbits require less launch energy than geostationary orbits, the ground station needs a steerable antenna to track the spacecraft, links must be switched between satellites, the range varies, there is a greater need for station keeping, the spacecraft will pass through the Van Allen radiation belt four times per day.
Similar orbits with an argument of perigee of 90° could allow high-latitude coverage in the southern hemisphere. A proposed constellation, the Antarctic Broadband Program, would have used satellites in an inverted Molniya orbit to provide broadband internet service to facilities in Antarctica. Funded by the now defunct Australian Space Research Program, it did not progress beyond initial development. Permanent high-elevation coverage of a large area of Earth requires a constellation of at least three spacecraft in Molniya orbits. If three spacecraft are used each spacecraft will be active for a period of eight hours per orbit, centered around apogee, as illustrated in figure 4. Figure 5 shows the satellite's field of view around the apogee; the Earth completes half a rotation in 12 hours, so the apogees of successive Molniya orbits will alternate between one half of the northern hemisphere and the other. For the original Molniya orbit, the apogees were placed over Russia and North America, but by changing the right ascension of the ascending node this can be varied.
The coverage from a satellite in a Molniya orbit over Russia is shown in figures 6 to 8, over North America in figures 9 to 11. The orbits of the three spacecraft should hav
North American Aerospace Defense Command
North American Aerospace Defense Command, known until March 1981 as the North American Air Defense Command, is a combined organization of the United States and Canada that provides aerospace warning, air sovereignty, protection for Northern America. Headquarters for NORAD and the NORAD/United States Northern Command center are located at Peterson Air Force Base in El Paso County, near Colorado Springs, Colorado; the nearby Cheyenne Mountain Complex has the Alternate Command Center. The NORAD commander and deputy commander are a United States four-star general or equivalent and a Canadian three-star general or equivalent. CINCNORAD maintains the NORAD headquarters at Peterson Air Force Base near Colorado Springs, Colorado; the NORAD and USNORTHCOM Command Center at Peterson AFB serves as a central collection and coordination facility for a worldwide system of sensors designed to provide the commander and the leadership of Canada and the U. S. with an accurate picture of any aerospace or maritime threat.
NORAD has administratively divided the North American landmass into three regions: Alaska NORAD Region - Eleventh Air Force Canadian NORAD Region - 1 Canadian Air Division Continental U. S. Region - First Air Force Both the CONR and CANR regions are divided into eastern and western sectors; the Alaskan NORAD Region maintains continuous capability to detect and warn off any atmospheric threat in its area of operations from its Regional Operations Control Center at Joint Base Elmendorf–Richardson, Alaska. ANR maintains the readiness to conduct a continuum of aerospace control missions, which include daily air sovereignty in peacetime and deterrence in time of tension, active air defense against manned and unmanned air-breathing atmospheric vehicles in times of crisis. ANR is supported by reserve units. Active duty forces are provided by 11 AF and the Canadian Armed Forces, reserve forces provided by the Alaska Air National Guard. Both 11 AF and the CAF provide active duty personnel to the ROCC to maintain continuous surveillance of Alaskan airspace.
Canadian NORAD Region Headquarters is at Manitoba. It was established on 22 April 1983, it is responsible for providing control of Canadian airspace. The Royal Canadian Air Force provides alert assets to NORAD. CANR is divided into two sectors, which are designated as the Canada East Sector and Canada West Sector. Both Sector Operations Control Centers are co-located at CFB North Bay Ontario; the routine operation of the SOCCs includes reporting track data, sensor status and aircraft alert status to NORAD headquarters. In 1996 CANR was moved to CFB Winnipeg. Canadian air defense forces assigned to NORAD include 409 Tactical Fighter Squadron at CFB Cold Lake, Alberta and 425 Tactical Fighter Squadron at CFB Bagotville, Quebec. All squadrons fly the McDonnell Douglas CF-18 Hornet fighter aircraft. To monitor for drug trafficking, in cooperation with the Royal Canadian Mounted Police and the United States drug law enforcement agencies, the Canadian NORAD Region monitors all air traffic approaching the coast of Canada.
Any aircraft that has not filed a flight plan may be directed to land and be inspected by RCMP and Canada Border Services Agency. The Continental NORAD Region is the component of NORAD that provides airspace surveillance and control and directs air sovereignty activities for the Contiguous United States. CONR is the NORAD designation of the United States Air Force First Air Force/AFNORTH, its headquarters is located at Florida. The First Air Force became responsible for the USAF air defense mission on 30 September 1990. AFNORTH is the United States Air Force component of United States Northern Command. 1 AF/CONR-AFNORTH comprises Air National Guard Fighter Wings assigned an air defense mission to 1 AF/CONR-AFNORTH on federal orders, made up of citizen Airmen. The primary weapons systems are the McDonnell Douglas F-15 Eagle and General Dynamics F-16 Fighting Falcon aircraft, it plans, controls and ensures air sovereignty and provides for the unilateral defense of the United States. It is organized with a combined First Air Force command post at Tyndall Air Force Base and two Sector Operations Control Centers at Rome, New York for the US East ROCC and McChord Field, Washington for the US West ROCC manned by active duty personnel to maintain continuous surveillance of CONUS airspace.
In its role as the CONUS NORAD Region, 1 AF/CONR-AFNORTH performs counter-drug surveillance operations. The United States Pacific Command would make the determination that an inbound missile is a threat to the United States in the Pacific Region. Hawaii is the only state in the United States with a pre-programmed Wireless Emergency Alert that can be sent to wireless devices if a ballistic missile is heading toward Hawaii. If the missile is fired from North Korea, the missile would take 20 minutes to reach Hawaii. PACOM would take less than 5 minutes to make a determination that the missile could strike Hawaii and would notify the Hawaii Emergency Management Agency. HI-EMA would issue the Civil Defense Warning that an inbound missile could strike Hawaii and that people should Shelter-in-Place: Get Inside, Stay Inside, Stay Tuned. People in Hawaii would have 12 to 15 minutes before impact. Federal Emergency Management Agency (F
Goddard Space Flight Center
The Goddard Space Flight Center is a major NASA space research laboratory located 6.5 miles northeast of Washington, D. C. in unincorporated Prince George's County, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC employs 10,000 civil servants and contractors, it is one of ten major NASA field centers, named in recognition of American rocket propulsion pioneer Dr. Robert H. Goddard. GSFC is within the former Goddard census-designated place. GSFC is the largest combined organization of scientists and engineers in the United States dedicated to increasing knowledge of the Earth, the Solar System, the Universe via observations from space. GSFC is a major US laboratory for operating unmanned scientific spacecraft. GSFC conducts scientific investigation and operation of space systems, development of related technologies. Goddard scientists can develop and support a mission, Goddard engineers and technicians can design and build the spacecraft for that mission. Goddard scientist John C.
Mather shared the 2006 Nobel Prize in Physics for his work on COBE. GSFC operates two spaceflight tracking and data acquisition networks and maintains advanced space and Earth science data information systems, develops satellite systems for the National Oceanic and Atmospheric Administration. GSFC manages operations for many NASA and international missions including the Hubble Space Telescope, the Explorers Program, the Discovery Program, the Earth Observing System, INTEGRAL, MAVEN, OSIRIS-REx, the Solar and Heliospheric Observatory, the Solar Dynamics Observatory, Swift. Past missions managed by GSFC include the Rossi X-ray Timing Explorer, Compton Gamma Ray Observatory, SMM, COBE, IUE, ROSAT. Unmanned earth observation missions and observatories in Earth orbit are managed by GSFC, while unmanned planetary missions are managed by the Jet Propulsion Laboratory in Pasadena, California. Goddard is NASA's first, oldest, space center, its original charter was to perform five major functions on behalf of NASA: technology development and fabrication, scientific research, technical operations, project management.
The center is organized into several directorates, each charged with one of these key functions. Until May 1, 1959, NASA's presence in Greenbelt, Maryland was known as the Beltsville Space Center, it was renamed the Goddard Space Flight Center, after Dr. Robert H. Goddard, its first 157 employees transferred from the United States Navy's Project Vanguard missile program, but continued their work at the Naval Research Laboratory in Washington, D. C. while the center was under construction. Goddard Space Flight Center contributed to Project Mercury, America's first manned space flight program; the Center assumed a lead role for the project in its early days and managed the first 250 employees involved in the effort, who were stationed at Langley Research Center in Hampton, Virginia. However, the size and scope of Project Mercury soon prompted NASA to build a new Manned Spacecraft Center, now the Johnson Space Center, in Houston, Texas. Project Mercury's personnel and activities were transferred there in 1961.
Goddard Space Flight Center remained involved in the manned space flight program, providing computer support and radar tracking of flights through a worldwide network of ground stations called the Spacecraft Tracking and Data Acquisition Network. However, the Center focused on designing unmanned satellites and spacecraft for scientific research missions. Goddard pioneered several fields of spacecraft development, including modular spacecraft design, which reduced costs and made it possible to repair satellites in orbit. Goddard's Solar Max satellite, launched in 1980, was repaired by astronauts on the Space Shuttle Challenger in 1984; the Hubble Space Telescope, launched in 1990, remains in service and continues to grow in capability thanks to its modular design and multiple servicing missions by the Space Shuttle. Today, the center remains involved in each of NASA's key programs. Goddard has developed more instruments for planetary exploration than any other organization, among them scientific instruments sent to every planet in the Solar System.
The Center's contribution to the Earth Science Enterprise includes several spacecraft in the Earth Observing System fleet as well as EOSDIS, a science data collection and distribution system. For the manned space flight program, Goddard develops tools for use by astronauts during extra-vehicular activity, operates the Lunar Reconnaissance Orbiter, a spacecraft designed to study the Moon in preparation for future manned exploration. Goddard's wooded campus is a few miles northeast of Washington, D. C. in Prince George's County. The center is on Greenbelt Road, Maryland Route 193. Baltimore, NASA Headquarters in Washington are 30–45 minutes away by highway. Greenbelt has a train station with access to the Washington Metro system and the MARC commuter train's Camden line; the High Bay Cleanroom located in building 29 is the world's largest ISO 7 cleanroom with 1.3 million cubic feet of space. Vacuum chambers in adjacent buildings 10 and 7 can be chilled or heated to +/- 200 °C. Adjacent building 15 houses the High Capacity Centrifuge, capable of generating 30 G on up to a 2.5 tons load.
Parsons Corporation assisted in the construction of the Class 10,000 cleanroom to support Hubble Space Telescope as well as other Goddard missions. The High Energy Astrophysics Science Archive Research Center is NASA's designated center for the archiving and
A geostationary orbit referred to as a geosynchronous equatorial orbit, is a circular geosynchronous orbit 35,786 km above Earth's equator and following the direction of Earth's rotation. An object in such an orbit appears motionless, at a fixed position in the sky, to ground observers. Communications satellites and weather satellites are placed in geostationary orbits, so that the satellite antennae that communicate with them do not have to rotate to track them, but can be pointed permanently at the position in the sky where the satellites are located. Using this characteristic, ocean-color monitoring satellites with visible and near-infrared light sensors can be operated in geostationary orbit in order to monitor sensitive changes of ocean environments. A geostationary orbit is a particular type of geosynchronous orbit, which has an orbital period equal to Earth's rotational period, or one sidereal day. Thus, the distinction is that, while an object in geosynchronous orbit returns to the same point in the sky at the same time each day, an object in geostationary orbit never leaves that position.
Geosynchronous orbits move around relative to a point on Earth's surface because, while geostationary orbits have an inclination of 0° with respect to the Equator, geosynchronous orbits have varying inclinations and eccentricities. The first appearance of a geostationary orbit in popular literature was in October, 1942, in the first Venus Equilateral story by George O. Smith, but Smith did not go into details. British science fiction author Arthur C. Clarke disseminated the idea with more details on how it would work, in a 1945 paper entitled "Extra-Terrestrial Relays — Can Rocket Stations Give Worldwide Radio Coverage?", published in Wireless World magazine. Clarke acknowledged the connection in his introduction to The Complete Venus Equilateral; the orbit, which Clarke first described as useful for broadcast and relay communications satellites, is sometimes called the Clarke Orbit. The Clarke Belt is the part of space about 35,786 km above sea level, in the plane of the equator, where near-geostationary orbits may be implemented.
The Clarke Orbit is about 265,000 km in circumference. Most commercial communications satellites, broadcast satellites and SBAS satellites operate in geostationary orbits. A geostationary transfer orbit is used to move a satellite from low Earth orbit into a geostationary orbit; the first satellite placed into a geostationary orbit was the Syncom-3, launched by a Delta D rocket in 1964. A worldwide network of operational geostationary meteorological satellites is used to provide visible and infrared images of Earth's surface and atmosphere; these satellite systems include: the United States GOES Meteosat, launched by the European Space Agency and operated by the European Weather Satellite Organization, EUMETSAT the Repulic of Korea COMS, GK-2A the Japanese Himawari Chinese Fengyun India's INSAT series A statite, a hypothetical satellite that uses a solar sail to modify its orbit, could theoretically hold itself in a geostationary "orbit" with different altitude and/or inclination from the "traditional" equatorial geostationary orbit.
Satellites in geostationary orbits are far enough away from Earth that communication latency becomes significant — about a quarter of a second for a trip from one ground-based transmitter to the satellite and back to another ground-based transmitter. For example, for ground stations at latitudes of φ = ±45° on the same meridian as the satellite, the time taken for a signal to pass from Earth to the satellite and back again can be computed using the cosine rule, given the geostationary orbital radius r, the Earth's radius R and the speed of light c, as Δ t = 2 c R 2 + r 2 − 2 R r cos φ ≈ 253 ms; this delay presents problems for latency-sensitive applications such as voice communication. Geostationary satellites are directly overhead at the equator and appear lower in the sky to an observer nearer the poles; as the observer's latitude increases, communication becomes more difficult due to factors such as atmospheric refraction, Earth's thermal emission, line-of-sight obstructions, signal reflections from the ground or nearby structures.
At latitudes above about 81°, geostationary satellites are below the horizon and cannot be seen at all. Because of this, some Russian communication satellites have used elliptical Molniya and Tundra orbits, which have excellent visibility at high latitudes. Satellites in geostationary orbit must all occupy a single ring above the equator; the requirement to space these satellites apart to avoid harmful radio-frequency interference during operations means that there are a limited number of orbital "slots" available, thus only a limited number of satellites can be operated in geostationary orbit. This has led to conflict between different countries wishing access to the same orbital slots and radio frequencies; these disputes are addressed through the International Telecommunication Union's allocation mechanism. In the 1976 Bogotá Declaration, eight countries located on the Earth's equator claimed sovereignty ov
In the context of spaceflight, a satellite is an artificial object, intentionally placed into orbit. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as Earth's Moon. On 4 October 1957 the Soviet Union launched the world's first artificial satellite, Sputnik 1. Since about 8,100 satellites from more than 40 countries have been launched. According to a 2018 estimate, some 4,900 remain in orbit, of those about 1,900. 500 operational satellites are in low-Earth orbit, 50 are in medium-Earth orbit, the rest are in geostationary orbit. A few large satellites have been assembled in orbit. Over a dozen space probes have been placed into orbit around other bodies and become artificial satellites to the Moon, Venus, Jupiter, Saturn, a few asteroids, a comet and the Sun. Satellites are used for many purposes. Among several other applications, they can be used to make star maps and maps of planetary surfaces, take pictures of planets they are launched into.
Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, space telescopes. Space stations and human spacecraft in orbit are satellites. Satellite orbits vary depending on the purpose of the satellite, are classified in a number of ways. Well-known classes include low Earth orbit, polar orbit, geostationary orbit. A launch vehicle is a rocket, it lifts off from a launch pad on land. Some are launched at sea aboard a plane. Satellites are semi-independent computer-controlled systems. Satellite subsystems attend many tasks, such as power generation, thermal control, attitude control and orbit control. "Newton's cannonball", presented as a "thought experiment" in A Treatise of the System of the World, by Isaac Newton was the first published mathematical study of the possibility of an artificial satellite. The first fictional depiction of a satellite being launched into orbit was a short story by Edward Everett Hale, The Brick Moon.
The idea surfaced again in Jules Verne's The Begum's Fortune. In 1903, Konstantin Tsiolkovsky published Exploring Space Using Jet Propulsion Devices, the first academic treatise on the use of rocketry to launch spacecraft, he calculated the orbital speed required for a minimal orbit, that a multi-stage rocket fuelled by liquid propellants could achieve this. In 1928, Herman Potočnik published The Problem of Space Travel -- The Rocket Motor, he described the use of orbiting spacecraft for observation of the ground and described how the special conditions of space could be useful for scientific experiments. In a 1945 Wireless World article, the English science fiction writer Arthur C. Clarke described in detail the possible use of communications satellites for mass communications, he suggested. The US military studied the idea of what was referred to as the "earth satellite vehicle" when Secretary of Defense James Forrestal made a public announcement on 29 December 1948, that his office was coordinating that project between the various services.
The first artificial satellite was Sputnik 1, launched by the Soviet Union on 4 October 1957, initiating the Soviet Sputnik program, with Sergei Korolev as chief designer. This in turn triggered the Space Race between the United States. Sputnik 1 helped to identify 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. Sputnik 2 was launched on 3 November 1957 and carried the first living passenger into orbit, a dog named Laika. In May, 1946, Project RAND had 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 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.
The United States Air Force's Project RAND released the report, but considered the satellite to be a tool for science and propaganda, rather than a potential military weapon. In 1954, the Secretary of Defense stated, "I know of no American satellite program." In February 1954 Project RAND released "Scientific Uses for a Satellite Vehicle," written 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. In the context of activities planned for the International Geophysical Year, 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 Soviets announced that they intended to launch a satellite by the fall of 1957. Following pressure by the American Rocket Society, the National Science Foundation, the International Geophysical Year, military interest picked up and in early 1955 the Army and Navy were worki