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Very Low Earth Orbit
Very low Earth orbit is a range of orbital altitudes below 400 km (250 mi), and is of increasing commercial importance in a variety of scenarios and for multiple applications, in both private and government satellite operations. Applications include earth observation, radar, infrared, weather, telecommunications, and rural internet access among others. Interest In 2009 governments started showing interest in VLEO satellites, such as the European Space Agency's scientific satellite " Gravity Field and Steady-State Ocean Circulation Explore" (GOCE), designed to take accurate measurements of Earth's gravitational field. It demonstrated a sustained orbit of between 250 and 300 km (155-186 mi ) for three years from 2009 to 2013. The Chinese Space Agency launched the Tiangong-1 space station into VLEO in 2011 orbiting at an average of 355 km (220 mi), and the Tiangong-2 in 2016, both which have since deorbited. The Tiangong launched in 2021, operates at ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. 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 a standardized bus to save cost and work, the most popular of which is small CubeSats. Similar satellites can work together as a group, forming constellations. Because of the high launch cost to space, 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 the surface to orbit by launch vehicles, high enough to avoid orbital decay by the atmosphere. Satellites can then change or maintain the orbit by pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DARPA
The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Advanced Research Projects Agency (ARPA), the agency was created on February 7, 1958, by President Dwight D. Eisenhower in response to the Soviet launching of Sputnik 1 in 1957. By collaborating with academia, industry, and government partners, DARPA formulates and executes research and development projects to expand the frontiers of technology and science, often beyond immediate U.S. military requirements.Dwight D. Eisenhower and Science & Technology, (2008). Dwight D. Eisenhower Memorial CommissionSource '' The Economist'' has called DARPA the agency "that shaped the modern world," and pointed out that " Moderna's COVID-19 vaccine sits alongside weather satellites, GPS, drones, stealth technology, voice interfaces, the personal comput ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allotropes Of Oxygen
There are several known allotropes of oxygen. The most familiar is molecular oxygen (O2), present at significant levels in Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highly reactive ozone (O3). Others are: *Atomic oxygen (O1), a free radical. *Singlet oxygen (O2*), one of two metastable states of molecular oxygen. * Tetraoxygen (O4), another metastable form. * Solid oxygen, existing in six variously colored phases, of which one is and another one metallic. Atomic oxygen Atomic oxygen, denoted O(3P) or O(3P), is very reactive, as the single atoms of oxygen tend to quickly bond with nearby molecules. On Earth's surface, it exists naturally for a very short time. In outer space, the presence of ample ultraviolet radiation results in a low Earth orbit atmosphere in which 96% of the oxygen occurs in atomic form. Ryan D. McCulla, Saint Louis University (2010). /acswebcontent.acs.org/prfar/2010/reports/P11141.html "Atomic Oxygen O(3P): P ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
International Space Station
The International Space Station (ISS) is the largest Modular design, modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA (Japan), European Space Agency, ESA (Europe), and Canadian Space Agency, CSA (Canada). The ownership and use of the space station is established by intergovernmental treaties and agreements. The station serves as a microgravity and space environment research laboratory in which Scientific research on the International Space Station, scientific research is conducted in astrobiology, astronomy, meteorology, physics, and other fields. The ISS is suited for testing the spacecraft systems and equipment required for possible future long-duration missions to the Moon and Mars. The International Space Station programme, ISS programme evolved from the Space Station Freedom, Space Station ''Freedom'', a 1984 American proposal to constr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inverse Square Law
In science, an inverse-square law is any scientific law stating that a specified physical quantity is inversely proportional to the square of the distance from the source of that physical quantity. The fundamental cause for this can be understood as geometric dilution corresponding to point-source radiation into three-dimensional space. Radar energy expands during both the signal transmission and the reflected return, so the inverse square for both paths means that the radar will receive energy according to the inverse fourth power of the range. To prevent dilution of energy while propagating a signal, certain methods can be used such as a waveguide, which acts like a canal does for water, or how a gun barrel restricts hot gas expansion to one dimension in order to prevent loss of energy transfer to a bullet. Formula In mathematical notation the inverse square law can be expressed as an intensity (I) varying as a function of distance (d) from some centre. The intensity is p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Power Density
Power density is the amount of power (time rate of energy transfer) per unit volume. In energy transformers including batteries, fuel cells, motors, power supply units etc., power density refers to a volume, where it is often called volume power density, expressed as W/m3. In reciprocating internal combustion engines, power density (power per swept volume or brake horsepower per cubic centimeter) is an important metric, based on the ''internal'' capacity of the engine, not its external size. Examples See also * Surface power density, energy per unit of area * Energy density, energy per unit volume * Specific energy, energy per unit mass *Power-to-weight ratio Power-to-weight ratio (PWR, also called specific power, or power-to-mass ratio) is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measuremen .../specific power, power per unit mass ** Specific absorption ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Space Debris
Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) are defunct human-made objects in space—principally in Geocentric orbit, Earth orbit—which no longer serve a useful function. These include derelict spacecraft—nonfunctional spacecraft and abandoned launch vehicle stages—mission-related debris, and particularly numerous in Earth orbit, fragmentation debris from the breakup of derelict rocket bodies and spacecraft. In addition to derelict human-made objects left in orbit, other examples of space debris include fragments from their disintegration, erosion and collisions or even paint flecks, solidified liquids expelled from spacecraft, and unburned particles from solid rocket motors. Space debris represents a risk to spacecraft. Space debris is typically a negative externality—it creates an external cost on others from the initial action to launch or use a spacecraft in near-Earth orbit—a cost that is typically not tak ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Satellite Constellation
A satellite constellation is a group of artificial satellites working together as a system. Unlike a single satellite, a constellation can provide permanent global or near-global coverage, such that at any time everywhere on Earth at least one satellite is visible. Satellites are typically placed in sets of complementary orbital planes and connect to globally distributed ground stations. They may also use inter-satellite communication. Other satellite groups Satellite constellations should not be confused with: * ''satellite clusters'', which are groups of satellites moving very close together in almost identical orbits (see satellite formation flying); * ''satellite series'' or ''satellite programs'' (such as Landsat), which are generations of satellites launched in succession; * ''satellite fleets'', which are groups of satellites from the same manufacturer or operator that function independently from each other (not as a system). Overview Satellites in Medium Earth or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High Frequency
High frequency (HF) is the International Telecommunication Union, ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decametre, decameters (ten to one hundred meters). Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances and for mountainous terrains which prevent Line-of-sight propagation, line-of-sight communica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thales Alenia Space
Thales Alenia Space () is a Franco-Italian aerospace manufacturer. A joint venture between the French technology corporation Thales Group (67%) and Italian defense conglomerate Leonardo (33%), the company is the largest satellite manufacturer in Europe. It is headquartered in Cannes, France. Thales Alenia Space designs and builds various space-related products, notably manufacturing numerous ranges of satellites for telecommunications, navigation, earth observation and space exploration purposes. The company is the second largest industrial participant in the International Space Station (ISS), having produced the European Space Agency's (ESA) modules for the ISS. It is also building satellites for Galileo, a European global satellite navigation system (GSNS). History Thales Alenia Space arose as a result of the French defense electronics specialist Thales Group deciding to buy out the participation of Alcatel in two joint-ventures between France's Alcatel and Italy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth Observation
Earth observation (EO) is the gathering of information about the physical, chemical, and biological systems of the planet Earth. It can be performed via remote-sensing technologies (Earth observation satellites) or through direct-contact sensors in ground-based or airborne platforms (such as weather stations and weather balloons, for example). According to the Group on Earth Observations (GEO), the concept encompasses both "space-based or remotely-sensed data, as well as ground-based or in situ data". Earth observation is used to monitor and assess the status of and changes in natural and built environments. Terminology In Europe, ''Earth observation'' has often been used to refer to satellite-based remote sensing, but the term is also used to refer to any form of observations of the Earth system, including in situ and airborne observations, for example. The GEO, which has over 100 member countries and over 100 participating organizations, uses EO in this broader sense. In ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Super Low Altitude Test Satellite
Super Low Altitude Test Satellite (SLATS) or Tsubame was a JAXA satellite intended to demonstrate operations in very low Earth orbit (VLEO, below 200 km), using ion engines to counteract aerodynamic drag from the Earth's atmosphere which is substantial at such lower orbital altitudes. It was launched on 23 December 2017, and decommissioned on 1 October 2019. The spacecraft was equipped with sensors to determine atomic oxygen density, an exposure facility to measure material degradation in the 200 km orbit, and a small camera. Initial designs had conventional, though slightly canted, solar panels (compare to the aerodynamic shape and on-body solar panels of GOCE, which flew in a 255 km orbit). SLATS received the nickname Tsubame (Japanese for barn swallow) on 14 July 2017. According to JAXA, this name was chosen as the thin, elongated satellite in super low orbit with a set of solar array wings was reminiscent of a small swallow flying low. SLATS was launched 23 De ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
