1.
Geostationary orbit
–
A geostationary orbit, geostationary Earth orbit or geosynchronous equatorial orbit is a circular orbit 35,786 kilometres above the Earths equator and following the direction of the Earths rotation. An object in such an orbit has a period equal to the Earths rotational period and thus appears motionless, at a fixed position in the sky. Using this characteristic, ocean color satellites with visible and near-infrared light sensors can also be operated in geostationary orbit in order to monitor sensitive changes of ocean environments, the notion of a geostationary space station equipped with radio communication was published in 1928 by Herman Potočnik. The first appearance of an orbit in popular literature was in the first Venus Equilateral story by George O. Smith. 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. Similarly, the Clarke Belt is the part of space about 35,786 km above sea level, in the plane of the equator, 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 an orbit was the Syncom-3. A worldwide network of operational geostationary meteorological satellites is used to provide visible and infrared images of Earths surface, a geostationary orbit can only be achieved at an altitude very close to 35,786 km and directly above the equator. This equates to a velocity of 3.07 km/s and an orbital period of 1,436 minutes. This ensures that the satellite will match the Earths rotational period and has a footprint on the ground. All geostationary satellites have to be located on this ring. 85° per year, to correct for this orbital perturbation, regular orbital stationkeeping manoeuvres are necessary, amounting to a delta-v of approximately 50 m/s per year. A second effect to be taken into account is the longitude drift, there are two stable and two unstable equilibrium points. Any geostationary object placed between the points would be slowly accelerated towards the stable equilibrium position, causing a periodic longitude variation. The correction of this effect requires station-keeping maneuvers with a maximal delta-v of about 2 m/s per year, solar wind and radiation pressure also exert small forces on satellites, over time, these cause them to slowly drift away from their prescribed orbits. In the absence of servicing missions from the Earth or a renewable propulsion method, hall-effect thrusters, which are currently in use, have the potential to prolong the service life of a satellite by providing high-efficiency electric propulsion. This delay presents problems for latency-sensitive applications such as voice communication, geostationary satellites are directly overhead at the equator and become lower in the sky the further north or south one travels. At latitudes above about 81°, geostationary satellites are below the horizon, because of this, some Russian communication satellites have used elliptical Molniya and Tundra orbits, which have excellent visibility at high latitudes
2.
Global Positioning System
–
The Global Positioning System is a space-based radionavigation system owned by the United States government and operated by the United States Air Force. The GPS system operates independently of any telephonic or internet reception, the GPS system provides critical positioning capabilities to military, civil, and commercial users around the world. The United States government created the system, maintains it, however, the US government can selectively deny access to the system, as happened to the Indian military in 1999 during the Kargil War. The U. S. Department of Defense developed the system and it became fully operational in 1995. Roger L. Easton of the Naval Research Laboratory, Ivan A, getting of The Aerospace Corporation, and Bradford Parkinson of the Applied Physics Laboratory are credited with inventing it. Announcements from Vice President Al Gore and the White House in 1998 initiated these changes, in 2000, the U. S. Congress authorized the modernization effort, GPS III. In addition to GPS, other systems are in use or under development, mainly because of a denial of access. The Russian Global Navigation Satellite System was developed contemporaneously with GPS, GLONASS can be added to GPS devices, making more satellites available and enabling positions to be fixed more quickly and accurately, to within two meters. There are also the European Union Galileo positioning system and Chinas BeiDou Navigation Satellite System, special and general relativity predict that the clocks on the GPS satellites would be seen by the Earths observers to run 38 microseconds faster per day than the clocks on the Earth. The GPS calculated positions would quickly drift into error, accumulating to 10 kilometers per day, the relativistic time effect of the GPS clocks running faster than the clocks on earth was corrected for in the design of GPS. The Soviet Union launched the first man-made satellite, Sputnik 1, two American physicists, William Guier and George Weiffenbach, at Johns Hopkinss Applied Physics Laboratory, decided to monitor Sputniks radio transmissions. Within hours they realized that, because of the Doppler effect, the Director of the APL gave them access to their UNIVAC to do the heavy calculations required. The next spring, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem — pinpointing the users location and this led them and APL to develop the TRANSIT system. In 1959, ARPA also played a role in TRANSIT, the first satellite navigation system, TRANSIT, used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour, in 1967, the U. S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology required by GPS. In the 1970s, the ground-based OMEGA navigation system, based on comparison of signal transmission from pairs of stations. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy, during the Cold War arms race, the nuclear threat to the existence of the United States was the one need that did justify this cost in the view of the United States Congress. This deterrent effect is why GPS was funded and it is also the reason for the ultra secrecy at that time
3.
GLONASS
–
GLONASS, or Global Navigation Satellite System, is a space-based satellite navigation system operating in the radionavigation-satellite service and used by the Russian Aerospace Defence Forces. It provides an alternative to GPS and is the second alternative navigational system in operation with global coverage, smartphones generally tend to use the same chipsets and the versions used since 2015 receive GLONASS signals and positioning information along with GPS. Since 2012, GLONASS was the second most used positioning system in mobile phones after GPS, the system has the advantage that smartphone users receive a more accurate reception identifying location to within 2 meters. Development of GLONASS began in the Soviet Union in 1976, beginning on 12 October 1982, numerous rocket launches added satellites to the system until the constellation was completed in 1995. After a decline in capacity during the late 1990s, in 2001, under Vladimir Putins presidency, GLONASS is the most expensive program of the Russian Federal Space Agency, consuming a third of its budget in 2010. By 2010, GLONASS had achieved 100% coverage of Russias territory and in October 2011, the GLONASS satellites designs have undergone several upgrades, with the latest version being GLONASS-K. GLONASS is a satellite navigation system, providing real time position and velocity determination for military. The satellites are located in middle circular orbit at 19,100 kilometres altitude with a 64.8 degree inclination, GLONASS orbit makes it especially suited for usage in high latitudes, where getting a GPS signal can be problematic. The constellation operates in three planes, with eight evenly spaced satellites on each. A fully operational constellation with global coverage consists of 24 satellites, to get a position fix the receiver must be in the range of at least four satellites. GLONASS satellites transmit two types of signal, open standard-precision signal L1OF/L2OF, and obfuscated high-precision signal L1SF/L2SF, the signals use similar DSSS encoding and binary phase-shift keying modulation as in GPS signals.0 MHz, known as the L1 band. The center frequency is 1602 MHz + n ×0.5625 MHz, signals are transmitted in a 38° cone, using right-hand circular polarization, at an EIRP between 25 and 27 dBW. The L2 band signals use the same FDMA as the L1 band signals, but transmit straddling 1246 MHz with the center frequency 1246 MHz + n×0.4375 MHz, the pseudo-random code is generated with a 9-stage shift register operating with a period of 1 ms. The navigational message is modulated at 50 bits per second, the superframe of the open signal is 7500 bits long and consists of 5 frames of 30 seconds, taking 150 seconds to transmit the continuous message. Each frame is 1500 bits long and consists of 15 strings of 100 bits, with 85 bits for data and check-sum bits, and 15 bits for time mark. Strings 1-4 provide immediate data for the satellite, and are repeated every frame, the data include ephemeris, clock and frequency offsets. Strings 5-15 provide non-immediate data for each satellite in the constellation, with frames I-IV each describing five satellites, the almanac uses modified Keplerian parameters and is updated daily. The details of the signal have not been disclosed
4.
Galileo (satellite navigation)
–
The €5 billion project is named after the Italian astronomer Galileo Galilei. The use of basic Galileo services will be free and open to everyone, the higher-precision capabilities will be available for paying commercial users. Galileo is intended to provide horizontal and vertical measurements within 1-metre precision. Galileo is to provide a new search and rescue function as part of the MEOSAR system. Satellites will be equipped with a transponder which will relay distress signals from emergency beacons to the Rescue coordination centre, which will then initiate a rescue operation. At the same time, the system is projected to provide a signal and this latter feature is new and is considered a major upgrade compared to the existing Cospas-Sarsat system, which does not provide feedback to the user. The first Galileo test satellite, the GIOVE-A, was launched 28 December 2005, as of December 2016 the system has 18 of 30 satellites in orbit. Galileo started offering Early Operational Capability on 15 December 2016 and is expected to reach Full Operational Capability in 2019, the complete 30-satellite Galileo system is expected by 2020. In 1999, the different concepts of the three main contributors of ESA for Galileo were compared and reduced to one by a joint team of engineers from all three countries. The first stage of the Galileo programme was agreed upon officially on 26 May 2003 by the European Union, the system is intended primarily for civilian use, unlike the more military-orientated systems of the United States, Russia, and China. The European system will only be subject to shutdown for military purposes in extreme circumstances and it will be available at its full precision to both civil and military users. On 17 January 2002, a spokesman for the stated that, as a result of US pressure and economic difficulties. A few months later, however, the situation changed dramatically, European Union member states decided it was important to have a satellite-based positioning and timing infrastructure that the US could not easily turn off in times of political conflict. The European Union and the European Space Agency agreed in March 2002 to fund the project, the starting cost for the period ending in 2005 is estimated at €1.1 billion. The required satellites were to be launched between 2011 and 2014, with the system up and running and under control from 2019. The final cost is estimated at €3 billion, including the infrastructure on Earth, the plan was for private companies and investors to invest at least two-thirds of the cost of implementation, with the EU and ESA dividing the remaining cost. The base Open Service is to be available without charge to anyone with a Galileo-compatible receiver, by early 2011 costs for the project had run 50% over initial estimates. Galileo is intended to be an EU civilian GNSS that allows all users access to it, initially GPS reserved the highest quality signal for military use, and the signal available for civilian use was intentionally degraded
5.
BeiDou Navigation Satellite System
–
The BeiDou Navigation Satellite System is a Chinese satellite navigation system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, the first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites and offers limited coverage and applications. It has been offering services, mainly for customers in China and neighboring regions. It became operational in China in December 2011, with 10 satellites in use and it is planned to begin serving global customers upon its completion in 2020. In-mid 2015, China started the build-up of the third generation BeiDou system in the global coverage constellation, the first BDS-3 satellite was launched 30 September 2015. As of March 2016,4 BDS-3 in-orbit validation satellites have been launched, the official English name of the system is BeiDou Navigation Satellite System. It is named after the Big Dipper constellation, which is known in Chinese as Běidǒu, the name literally means Northern Dipper, the name given by ancient Chinese astronomers to the seven brightest stars of the Ursa Major constellation. Historically, this set of stars was used in navigation to locate the North Star Polaris, as such, the name BeiDou also serves as a metaphor for the purpose of the satellite navigation system. The original idea of a Chinese satellite navigation system was conceived by Chen Fangyun, the third satellite, BeiDou-1C, was put into orbit on 25 May 2003. The successful launch of BeiDou-1C also meant the establishment of the BeiDou-1 navigation system. On 2 November 2006, China announced that from 2008 BeiDou would offer a service with an accuracy of 10 meters, timing of 0.2 microseconds. In February 2007, the fourth and last satellite of the BeiDou-1 system and it was reported that the satellite had suffered from a control system malfunction but was then fully restored. In April 2007, the first satellite of BeiDou-2, namely Compass-M1 was successfully put into its working orbit, the second BeiDou-2 constellation satellite Compass-G2 was launched on 15 April 2009. On 2 June 2010, the satellite was launched successfully into orbit. The fifth orbiter was launched into space from Xichang Satellite Launch Center by an LM-3I carrier rocket on 1 August 2010, three months later, on 1 November 2010, the sixth satellite was sent into orbit by LM-3C. Another satellite, the Beidou-2/Compass IGSO-5 satellite, was launched from the Xichang Satellite Launch Center by a Long March-3A on 1 December 2011. In September 2003, China intended to join the European Galileo positioning system project and was to invest €230 million in Galileo over the few years. At the time, it was believed that Chinas BeiDou navigation system would only be used by its armed forces
6.
International Space Station
–
The International Space Station is a space station, or a habitable artificial satellite, in low Earth orbit. Its first component launched into orbit in 1998, and the ISS is now the largest man-made body in space, the ISS consists of pressurised modules, external trusses, solar arrays, and other components. ISS components have been launched by Russian Proton and Soyuz rockets, the ISS serves as a microgravity and space environment research laboratory in which crew members conduct experiments in biology, human biology, physics, astronomy, meteorology, and other fields. The station is suited for the testing of systems and equipment required for missions to the Moon. The ISS maintains an orbit with an altitude of between 330 and 435 km by means of reboost manoeuvres using the engines of the Zvezda module or visiting spacecraft and it completes 15.54 orbits per day. The ISS is the space station to be inhabited by crews, following the Soviet and later Russian Salyut, Almaz. The station has continuously occupied for 16 years and 156 days since the arrival of Expedition 1 on 2 November 2000. This is the longest continuous presence in low Earth orbit. It has been visited by astronauts, cosmonauts and space tourists from 17 different nations, Soyuz has very limited downmass capability. The ISS programme is a joint project among five participating space agencies, NASA, Roscosmos, JAXA, ESA, the ownership and use of the space station is established by intergovernmental treaties and agreements. The station is divided two sections, the Russian Orbital Segment and the United States Orbital Segment, which is shared by many nations. As of January 2014, the American portion of ISS is being funded until 2024, Roscosmos has endorsed the continued operation of ISS through 2024 but has proposed using elements of the Russian Orbital Segment to construct a new Russian space station called OPSEK. On 28 March 2015, Russian sources announced that Roscosmos and NASA had agreed to collaborate on the development of a replacement for the current ISS. NASA later issued a statement expressing thanks for Russias interest in future co-operation in space exploration. According to the original Memorandum of Understanding between NASA and Rosaviakosmos, the International Space Station was intended to be a laboratory, observatory and factory in low Earth orbit. It was also planned to provide transportation, maintenance, and act as a base for possible future missions to the Moon, Mars. In the 2010 United States National Space Policy, the ISS was given roles of serving commercial, diplomatic. The ISS provides a platform to conduct scientific research, the ISS simplifies individual experiments by eliminating the need for separate rocket launches and research staff
7.
Hubble Space Telescope
–
The Hubble Space Telescope is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. Although not the first space telescope, Hubble is one of the largest and most versatile, with a 2. 4-meter mirror, Hubbles four main instruments observe in the near ultraviolet, visible, and near infrared spectra. Hubbles orbit outside the distortion of Earths atmosphere allows it to take extremely high-resolution images, Hubble has recorded some of the most detailed visible light images ever, allowing a deep view into space and time. Many Hubble observations have led to breakthroughs in astrophysics, such as determining the rate of expansion of the universe. The HST was built by the United States space agency NASA, the Space Telescope Science Institute selects Hubbles targets and processes the resulting data, while the Goddard Space Flight Center controls the spacecraft. Space telescopes were proposed as early as 1923, Hubble was funded in the 1970s, with a proposed launch in 1983, but the project was beset by technical delays, budget problems, and the Challenger disaster. When finally launched in 1990, Hubbles main mirror was found to have been ground incorrectly, the optics were corrected to their intended quality by a servicing mission in 1993. Hubble is the telescope designed to be serviced in space by astronauts. After launch by Space Shuttle Discovery in 1990, five subsequent Space Shuttle missions repaired, upgraded, the fifth mission was canceled on safety grounds following the Columbia disaster. However, after spirited public discussion, NASA administrator Mike Griffin approved the fifth servicing mission, the telescope is operating as of 2017, and could last until 2030–2040. Its scientific successor, the James Webb Space Telescope, is scheduled for launch in 2018, the history of the Hubble Space Telescope can be traced back as far as 1946, to the astronomer Lyman Spitzers paper Astronomical advantages of an extraterrestrial observatory. In it, he discussed the two advantages that a space-based observatory would have over ground-based telescopes. First, the resolution would be limited only by diffraction, rather than by the turbulence in the atmosphere. Second, a telescope could observe infrared and ultraviolet light. Spitzer devoted much of his career to pushing for the development of a space telescope, space-based astronomy had begun on a very small scale following World War II, as scientists made use of developments that had taken place in rocket technology. An orbiting solar telescope was launched in 1962 by the United Kingdom as part of the Ariel space program, oAO-1s battery failed after three days, terminating the mission. It was followed by OAO-2, which carried out observations of stars and galaxies from its launch in 1968 until 1972. The continuing success of the OAO program encouraged increasingly strong consensus within the community that the LST should be a major goal
8.
Iridium satellite constellation
–
The Iridium satellite constellation is a satellite constellation providing voice and data coverage to satellite phones, pagers and integrated transceivers over the Earths entire surface. Iridium Communications owns and operates the constellation and sells equipment and access to its services, the constellation consists of 66 active satellites in orbit required for global coverage, and additional spare satellites to serve in case of failure. Satellites are in low Earth orbit at a height of approximately 485 mi, orbital velocity of the satellites is approximately 17,000 mph. Satellites communicate with neighboring satellites via Ka band inter-satellite links, each satellite can have four inter-satellite links, two to neighbors fore and aft in the same orbital plane, and two to satellites in neighboring planes to either side. The satellites orbit from pole to pole with an orbital period of roughly 100 minutes. This design means there is excellent satellite visibility and service coverage even at the North and South poles. The over-the-pole orbital design produces seams where satellites in counter-rotating planes next to one another are traveling in opposite directions, the constellation of 66 active satellites has 6 orbital planes spaced 30 degrees apart, with 11 satellites in each plane. This reduced set of 6 planes is sufficient to cover the entire Earths surface at every moment, because of the shape of the Iridium satellites reflective antennas, the satellites focus sunlight on a small area of the Earths surface in an incidental manner. This results in an effect called Iridium flares, where the satellite appears as one of the brightest objects in the night sky. The Iridium satellite constellation was conceived in the early 1990s, as a way to reach high Earth latitudes with reliable satellite communication services, early calculations showed that 77 satellites would be needed, hence the name Iridium – after the metal with atomic number 77. It turned out that just 66 were required to complete the blanket coverage of the planet with communication services, the constellation was launched to orbit in the late 1990s and the first telephone call was made over the network in 1998. However, although the system met its requirements, it was not a success in the market. Insufficient market demand existed for the product at the points on offer from Iridium as set by its parent company Motorola. The company failed to earn revenue sufficient to service the debt associated with building out the constellation and Iridium went bankrupt, the constellation continued following the bankruptcy of the original Iridium corporation. Users include journalists, explorers, and military units, the satellites each contain seven Motorola/Freescale PowerPC 603E processors running at roughly 200 MHz, connected by a custom backplane network. One processor is dedicated to each antenna, and two processors are dedicated to satellite control, one being a spare. Late in the project an extra processor was added to perform resource management, the cellular look down antenna has 48 spot beams arranged as 16 beams in three sectors. The four inter-satellite cross links on each operate at 10 Mbit/s
9.
Van Allen radiation belt
–
A radiation belt is a zone of energetic charged particles, most of which originate from the solar wind that is captured by and held around a planet by that planets magnetic field. The Earth has two belts and sometimes others may be temporarily created. The discovery of the belts is credited to James Van Allen, Earths two main belts extend from an altitude of about 1,000 to 60,000 kilometers above the surface in which region radiation levels vary. Most of the particles form the belts are thought to come from solar wind. By trapping the solar wind, the magnetic field deflects those energetic particles, the belts are located in the inner region of the Earths magnetosphere. The belts trap energetic electrons and protons, other nuclei, such as alpha particles, are less prevalent. The belts endanger satellites, which must have their sensitive components protected with adequate shielding if they spend significant time in that zone, kristian Birkeland, Carl Størmer, and Nicholas Christofilos had investigated the possibility of trapped charged particles before the Space Age. Explorer 1 and Explorer 3 confirmed the existence of the belt in early 1958 under James Van Allen at the University of Iowa, the trapped radiation was first mapped by Explorer 4, Pioneer 3 and Luna 1. The term Van Allen belts refers specifically to the radiation belts surrounding Earth, however, the Sun does not support long-term radiation belts, as it lacks a stable, global, dipole field. The Earths atmosphere limits the belts particles to regions above 200–1,000 km, the belts are confined to a volume which extends about 65° on either side of the celestial equator. The NASA Van Allen Probes mission aims at understanding how populations of relativistic electrons and ions in space form or change in response to changes in solar activity, the Van Allen Probes mission successfully launched on August 30,2012. The primary mission is scheduled to last two years with expendables expected to last four, NASAs Goddard Space Flight Center manages the Living With a Star program of which the Van Allen Probes is a project, along with Solar Dynamics Observatory. The Applied Physics Laboratory is responsible for the implementation and instrument management for the Van Allen Probes, Radiation belts exist around other planets and moons in the solar system that have magnetic fields powerful enough to sustain them. To date, most of these belts have been poorly mapped. The Voyager Program only nominally confirmed the existence of similar belts around Uranus, the inner Van Allen Belt extends typically from an altitude of 0.2 to 2 Earth radii or 1,000 km to 6,000 km above the Earth. In certain cases when solar activity is stronger or in areas such as the South Atlantic Anomaly. The inner belt contains high concentrations of electrons in the range of hundreds of keV and energetic protons with energies exceeding 100 MeV, the source of lower energy protons is believed to be proton diffusion due to changes in the magnetic field during geomagnetic storms. Due to the offset of the belts from Earths geometric center
10.
Earth
–
Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally 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 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost 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 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.
