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
Ideal gas law
The ideal gas law called the general gas equation, is the equation of state of a hypothetical ideal gas. It is a good approximation of the behavior of many gases under many conditions, although it has several limitations, it was first stated by Émile Clapeyron in 1834 as a combination of the empirical Boyle's law, Charles's law, Avogadro's law, Gay-Lussac's law. The ideal gas law is written as P V = n R T, where P, V and T are the pressure and absolute temperature, it is the same for all gases. It can be derived from the microscopic kinetic theory, as was achieved by August Krönig in 1856 and Rudolf Clausius in 1857; the state of an amount of gas is determined by its pressure and temperature. The modern form of the equation relates these in two main forms; the temperature used in the equation of state is an absolute temperature: the appropriate SI unit is the kelvin. The most introduced form is P V = n R T = N k B T, where: P is the pressure of the gas, V is the volume of the gas, n is the amount of substance of gas, N is the number of gas molecules, R is the ideal, or universal, gas constant, equal to the product of the Boltzmann constant and the Avogadro constant, k B is the Boltzmann constant T is the absolute temperature of the gas.
In SI units, P is measured in pascals, V is measured in cubic metres, n is measured in moles, T in kelvins. R has the value 8.314 J/ ≈ 2 cal/, or 0.08206 L·atm/. How much gas is present could be specified by giving the mass instead of the chemical amount of gas. Therefore, an alternative form of the ideal gas law may be useful; the chemical amount is equal to total mass of the gas divided by the molar mass: n = m M. By replacing n with m/M and subsequently introducing density ρ = m/V, we get: P V = m M R T P = m V R T M P = ρ R M T Defining the specific gas constant Rspecific as the ratio R/M, P = ρ R specific T This form of the ideal gas law is useful because it links pressure and temperature in a unique formula independent of the quantity of the considered gas. Alternatively, the law may be written in terms of the specific volume v, the reciprocal of density, as P v = R specific T, it is common in engineering applications, to represent the specific gas constant by the symbol R. In such cases, the universal gas constant is given a different symbol such as R ¯ to distinguish it.
In any case, the context and/or units of the gas constant should make it clear as to whether the universal or specific gas constant is being referred to. In statistical mechanics the following molecular equation is derived from first principles P = n k B T, where P is the absolute pressure of the gas, n is the number of molecules in the given volume V, T is the absolute temperature, kB is the Boltzmann constant relating temperature and energy, given by: k B = R N A where NA is the Avogadro constant. From this we notice that for a gas of mass m, with an average particle mass of μ times the atomic mass constant, mu, the number of molecules will be given by N = m μ m u, since ρ = m/V = nμmu, we find that the ideal gas law can be rewritten as P = 1 V m μ m u k B T = k B μ m u ρ T. In SI units, P is measured in pascals, V in cubic metre
Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics. Thermodynamic temperature is defined by the third law of thermodynamics in which the theoretically lowest temperature is the null or zero point. At this point, absolute zero, the particle constituents of matter have minimal motion and can become no colder. In the quantum-mechanical description, matter at absolute zero is in its ground state, its state of lowest energy. Thermodynamic temperature is also called absolute temperature, for two reasons: one, proposed by Kelvin, that it does not depend on the properties of a particular material; the International System of Units specifies a particular scale for thermodynamic temperature. It uses the kelvin scale for measurement and selects the triple point of water at 273.16 K as the fundamental fixing point. Other scales have been in use historically; the Rankine scale, using the degree Fahrenheit as its unit interval, is still in use as part of the English Engineering Units in the United States in some engineering fields.
ITS-90 gives a practical means of estimating the thermodynamic temperature to a high degree of accuracy. The temperature of a body at rest is a measure of the mean of the energy of the translational and rotational motions of matter's particle constituents, such as molecules and subatomic particles; the full variety of these kinetic motions, along with potential energies of particles, occasionally certain other types of particle energy in equilibrium with these, make up the total internal energy of a substance. Internal energy is loosely called the heat energy or thermal energy in conditions when no work is done upon the substance by its surroundings, or by the substance upon the surroundings. Internal energy may be stored in a number of ways within a substance, each way constituting a "degree of freedom". At equilibrium, each degree of freedom will have on average the same energy: k B T / 2 where k B is the Boltzmann constant, unless that degree of freedom is in the quantum regime; the internal degrees of freedom may be in the quantum regime at room temperature, but the translational degrees of freedom will be in the classical regime except at low temperatures and it may be said that, for most situations, the thermodynamic temperature is specified by the average translational kinetic energy of the particles.
Temperature is a measure of the random submicroscopic motions and vibrations of the particle constituents of matter. These motions comprise the internal energy of a substance. More the thermodynamic temperature of any bulk quantity of matter is the measure of the average kinetic energy per classical degree of freedom of its constituent particles. "Translational motions" are always in the classical regime. Translational motions are ordinary, whole-body movements in three-dimensional space in which particles move about and exchange energy in collisions. Figure 1 below shows translational motion in gases. Thermodynamic temperature's null point, absolute zero, is the temperature at which the particle constituents of matter are as close as possible to complete rest. Zero kinetic energy remains in a substance at absolute zero. Throughout the scientific world where measurements are made in SI units, thermodynamic temperature is measured in kelvins. Many engineering fields in the U. S. however, measure thermodynamic temperature using the Rankine scale.
By international agreement, the unit kelvin and its scale are defined by two points: absolute zero, the triple point of Vienna Standard Mean Ocean Water. Absolute zero, the lowest possible temperature, is defined as being 0 K and −273.15 °C. The triple point of water is defined as being 273.16 K and 0.01 °C. This definition does three things: It fixes the magnitude of the kelvin unit as being 1 part in 273.16 parts the difference between absolute zero and the triple point of water. Temperatures expressed in kelvins are converted to degrees Rankine by multiplying by 1.8. Temperatures expressed in degrees Rankine are converted to kelvins by dividing by 1.8. Although the kelvin and Celsius scales are defined using absolute zero and the triple point of water, it is impractical to use this definition at temperatures that are different from the triple point of water. ITS-90 is designed to represent the thermodynamic temperature as as possible throughout its range. Many different thermometer designs are required to cover the entire range.
These include helium vapor pressure thermometers, helium gas thermometers, standard platinum resistance thermometers and monochromatic radiation thermometers. For some types of thermometer the relationship between the property observed and temperature, is close to linear, so for most purposes a linear scale is sufficient, without point-by-point calibration
The troposphere is the lowest layer of Earth's atmosphere, is where nearly all weather conditions take place. It contains 75% of the atmosphere's mass and 99% of the total mass of water vapor and aerosols; the average height of the troposphere is 18 km in the tropics, 17 km in the middle latitudes, 6 km in the polar regions in winter. The total average height of the troposphere is 13 km; the lowest part of the troposphere, where friction with the Earth's surface influences air flow, is the planetary boundary layer. This layer is a few hundred meters to 2 km deep depending on the landform and time of day. Atop the troposphere is the tropopause, the border between the troposphere and stratosphere; the tropopause is an inversion layer, where the air temperature ceases to decrease with height and remains constant through its thickness. The word troposphere is derived from the Greek tropos and sphere, reflecting the fact that rotational turbulent mixing plays an important role in the troposphere's structure and behaviour.
Most of the phenomena associated with day-to-day weather occur in the troposphere. By volume, dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, small amounts of other gases. Air contains a variable amount of water vapor. Except for the water vapor content, the composition of the troposphere is uniform; the source of water vapor is at the Earth's surface through the process of evaporation. The temperature of the troposphere decreases with altitude. And, saturation vapor pressure decreases as temperature drops. Hence, the amount of water vapor that can exist in the atmosphere decreases with altitude and the proportion of water vapor is greatest near the surface of the Earth; the pressure of the atmosphere decreases with altitude. This is because the atmosphere is nearly in hydrostatic equilibrium so that the pressure is equal to the weight of air above a given point; the change in pressure with altitude can be equated to the density with the hydrostatic equation d P d z = − ρ g n = − m P g n R T where: gn is the standard gravity ρ is the densityz is the altitude P is the pressure R is the gas constant T is the thermodynamic temperature m is the molar massSince temperature in principle depends on altitude, one needs a second equation to determine the pressure as a function of altitude as discussed in the next section.
The temperature of the troposphere decreases as altitude increases. The rate at which the temperature decreases, is called the environmental lapse rate; the ELR is nothing more than the difference in temperature between the surface and the tropopause divided by the height. The ELR assumes that the air is still, i.e. that there is no mixing of the layers of air from vertical convection, nor winds that would create turbulence and hence mixing of the layers of air. The reason for this temperature difference is that the ground absorbs most of the sun's energy, which heats the lower levels of the atmosphere with which it is in contact. Meanwhile, the radiation of heat at the top of the atmosphere results in the cooling of that part of the atmosphere; the ELR assumes as air is heated it becomes buoyant and rises. The dry adiabatic lapse rate accounts for the effect of the expansion of dry air as it rises in the atmosphere and wet adiabatic lapse rates includes the effect of the condensation of water vapor on the lapse rate.
When a parcel of air rises, it expands. As the air parcel expands, it pushes the surrounding air outward, transferring energy in the form of work from that parcel to the atmosphere; as energy transfer to a parcel of air by way of heat is slow, it is assumed to not exchange energy by way of heat with the environment. Such a process is called an adiabatic process. Since the rising parcel of air is losing energy as it does work on the surrounding atmosphere and no energy is transferred into it as heat from the atmosphere to make up for the loss, the parcel of air is losing energy, which manifests itself as a decrease in the temperature of the air parcel; the reverse, of course, will be true for a parcel of air, sinking and is being compressed. Since the process of compression and expansion of an air parcel can be considered reversible and no energy is transferred into or out of the parcel, such a process is considered isentropic, meaning that there is no change in entropy as the air parcel rises and falls, d S = 0.
Since the heat exchanged d Q = 0 is related to the entropy change d S by d Q = T d S, the equation governing the temperature as a function of height for a mixed atmosphere is d S d z = 0 where S is the entropy. The above equation states; the rate at which temperature decreases with height u
International Civil Aviation Organization
The International Civil Aviation Organization is a specialized agency of the United Nations. It codifies the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth, its headquarters is located in the Quartier International of Montreal, Canada. The ICAO Council adopts standards and recommended practices concerning air navigation, its infrastructure, flight inspection, prevention of unlawful interference, facilitation of border-crossing procedures for international civil aviation. ICAO defines the protocols for air accident investigation followed by transport safety authorities in countries signatory to the Chicago Convention on International Civil Aviation; the Air Navigation Commission is the technical body within ICAO. The Commission is composed of 19 Commissioners, nominated by the ICAO's contracting states, appointed by the ICAO Council. Commissioners serve as independent experts, who although nominated by their states, do not serve as state or political representatives.
The development of international Standards And Recommended Practices is done under the direction of the ANC through the formal process of ICAO Panels. Once approved by the Commission, standards are sent to the Council, the political body of ICAO, for consultation and coordination with the Member States before final adoption. ICAO is distinct from other international air transport organizations, like the International Air Transport Association, a trade association representing airlines; the forerunner to ICAO was the International Commission for Air Navigation. It held its first convention in 1903 in Berlin, but no agreements were reached among the eight countries that attended. At the second convention in 1906 held in Berlin, 27 countries attended; the third convention, held in London in 1912 allocated the first radio callsigns for use by aircraft. ICAN continued to operate until 1945. Fifty-two countries signed the Chicago Convention on International Civil Aviation known as the Chicago Convention, in Chicago, Illinois, on 7 December 1944.
Under its terms, a Provisional International Civil Aviation Organization was to be established, to be replaced in turn by a permanent organization when 26 countries ratified the convention. Accordingly, PICAO began operating on 6 June 1945, replacing ICAN; the 26th country ratified the Convention on 5 March 1947 and PICAO was disestablished on 4 April 1947 and replaced by ICAO, which began operations the same day. In October 1947, ICAO became an agency of the United Nations linked to the United Nations Economic and Social Council. In April 2013 Qatar offered to serve as the new permanent seat of the Organization. Qatar promised to construct a massive new headquarters for ICAO and cover all moving expenses, stating that Montreal "was too far from Europe and Asia", "had cold winters," was hard to attend due to the refusal of the Canadian government to provide visas in a timely manner, that the taxes imposed on ICAO by Canada were too high. According to The Globe and Mail, Qatar's move was at least motivated by the pro-Israel foreign policy of Canadian Prime Minister Stephen Harper.
One month Qatar withdrew its bid after a separate proposal to the ICAO's governing council to move the ICAO triennial conference to Doha was defeated by a vote of 22–14. The 9th edition of the Convention on International Civil Aviation includes modifications from 1948 up to year 2006. ICAO refers to its current edition of the Convention as the Statute, designates it as ICAO Document 7300/9; the Convention has 19 Annexes that are listed by title in the article Convention on International Civil Aviation. As of January 2019, there are 192 ICAO members, consisting of 191 of the 193 UN members, plus the Cook Islands. Liechtenstein has delegated Switzerland to enter into the treaty on its behalf and the treaty applies in the territory of Liechtenstein; the Republic of China was a founding member of ICAO but was replaced by People's Republic of China as the legal representative of China in 1971 and as such, did not take part in the organization. In 2013, the Republic of China was for the first time invited to attend 38th session of ICAO Assembly as a guest under the name of Chinese Taipei.
The Council of ICAO is elected by the Assembly every 3 years and consists of 36 members elected in 3 groups. The present Council was elected on 4 October 2016 at the 39th Assembly of ICAO at Montreal; the structure of the present Council is as follows: ICAO standardizes certain functions for use in the airline industry, such as the Aeronautical Message Handling System. This makes it a standards organization; each country should have an accessible Aeronautical Information Publication, based on standards defined by ICAO, containing information essential to air navigation. Countries are required to update their AIP manuals every 28 days and so provide definitive regulations and information for each country about airspace and airports. ICAO's standards dictate that temporary hazards to aircraft are published using NOTAMs. ICAO defines an International Standard Atmosphere, a model of the standard variation of pressure, temperature and viscosity with altitude in the Earth's atmosphere; this is useful in designing aircraft.
United States Naval Research Laboratory
The United States Naval Research Laboratory is the corporate research laboratory for the United States Navy and the United States Marine Corps. It conducts applied research, technological development and prototyping; the laboratory's specialties include plasma physics, space physics, materials science, tactical electronic warfare. NRL is one of the first US Government scientific R&D laboratories, having opened in 1923 at the instigation of Thomas Edison, is under the Office of Naval Research. NRL's research expenditures are $1 billion per year; the Naval Research Laboratory conducts a variety of basic and scientific research and technological development of importance to the Navy. It has a history of scientific breakthroughs and technological achievements dating back to its foundation in 1923. In some instances the laboratory's contributions to military technology have been declassified decades after those technologies have become adopted. In 2011, NRL researchers published 1,398 unclassified scientific & technical articles, book chapters and conference proceedings.
In 2008, the NRL was ranked No. 3 among all U. S. institutions holding nanotechnology-related patents, behind IBM and the University of California. Current areas of research at NRL include: Advanced radio and infrared sensors Autonomous systems Computer science and artificial intelligence Directed energy technology Electronic electro-optical device technology Electronic warfare Enhanced maintainability and survivability technology Environmental effects on naval systems Imaging research and systems Information technology Marine geosciences Materials Meteorology Ocean acoustics Oceanography Space systems and technology Surveillance and sensor technology Undersea technologyIn 2014, the NRL was researching: armor for munitions in transport, high-powered lasers, remote explosives detection, the dynamics of explosive gas mixtures, electromagnetic Railgun technology, detection of hidden nuclear materials, graphene devices, high-power high frequency amplifiers, acoustic lensing, information-rich orbital coastline mapping, arctic weather forecasting, global aerosol analysis & prediction, high-density plasmas, Millisecond pulsars, broadband laser data links, virtual mission operation centers, battery technology, photonic crystals, carbon nanotube electronics, electronic sensors, mechanical nano-resonators, solid-state chemical sensors, organic opto-electronics, neural-electronic interfaces and self-assembling nanostructures.
The laboratory includes a range of R&D facilities. 2014 additions included the NRL Nanoscience Institute's 5,000 sq ft Class 100 nanofabrication cleanroom. The Naval Research Laboratory has a long history of spacecraft development; this includes the second and seventh American satellites in Earth orbit, the first solar-powered satellite, the first surveillance satellite, the first meteorological satellite and the first GPS satellite. Project Vanguard, the first American satellite program, tasked NRL with the design and launch of an artificial satellite, accomplished in 1958; as of 2013, Vanguard I and its upper launch stage are still in orbit, making them the longest-lived man-made satellites. Vanguard II was the first satellite to observe the Earth's cloud cover and therefore the first meteorological satellite. NRL's Galactic Radiation and Background I was the first U. S. intelligence satellite, mapping out Soviet radar networks from space. The Global Positioning System was tested by NRL's Timation series of satellites.
The first operational GPS satellite, Timation IV was designed and constructed at NRL. NRL pioneered the study of the sun Ultraviolet and X-Ray spectrum and continues to contribute to the field with satellites like Coriolis launched in 2003. NRL is responsible for the Tactical Satellite Program with spacecraft launched in 2006, 2009 and 2011; the NRL designed the first satellite tracking system, which became the prototype for future satellite tracking networks. Prior to the success of surveillance satellites, the iconic parabolic antenna atop NRL's main headquarters in Washington, D. C. was part of Communication Moon Relay, a project that utilized signals bounced off the Moon both for long-distance communications research and surveillance of internal Soviet transmissions during the Cold War. NRL's spacecraft development program continues today with the TacSat-4 experimental tactical reconnaissance and communication satellite. In addition to spacecraft design, NRL designs and operates spaceborne research instruments and experiments, such as the Strontium Iodide Radiation Instrumentation and RAM Angle and Magnetic field sensor aboard STPSat-5, the Wide-field imager for solar probe aboard the Parker Solar Probe, the Large Angle and Spectrometric Coronagraph Experiment aboard the Solar and Heliospheric Observatory.
NASA's Fermi Gamma-ray Space Telescope was tested at NRL spacecraft testing facilities. NRL scientists have most contributed leading research to the study of novas and gamma ray bursts; the Marine Meteorology Division, located in Monterey, contributes to weather forecasting in the United States and around the world by publishing imagery from 18 weather satellites. Satellite images of severe weather that are used for advanced warning originate from NRL–MRY, as seen in 2017 during hurricane Harvey. NRL is involved in weather forecasting models such as the
Geopotential height or geopotential altitude is a vertical coordinate referenced to Earth's mean sea level, an adjustment to geometric height using the variation of gravity with latitude and vertical position. Thus, it can be considered a "gravity-adjusted height". One speaks of the geopotential height of a certain pressure level, which would correspond to the geopotential height at which that pressure occurs. At an elevation of h, the geopotential is defined as: Φ = ∫ 0 h g d z, where g is the acceleration due to gravity, ϕ is latitude, z is the geometric elevation, thus geopotential is the gravitational potential energy per unit mass at that elevation h. The geopotential height is: Z g = Φ g 0, which normalizes the geopotential to g0, the standard gravity at mean sea level. Geophysical scientists use geopotential height as a function of pressure rather than pressure as a function of geometric height, because doing so in many cases makes analytical calculations more convenient. For example, the primitive equations which weather forecast models solve are more expressed in terms of geopotential than geometric height.
Using the former eliminates air density from the equations. A plot of geopotential height for a single pressure level shows the troughs and ridges and lows, which are seen on upper air charts; the geopotential thickness between pressure levels – difference of the 850 hPa and 1000 hPa geopotential heights for example – is proportional to mean virtual temperature in that layer. Geopotential height contours can be used to calculate the geostrophic wind, faster where the contours are more spaced and tangential to the geopotential height contours; the National Weather Service defines geopotential height as: "...roughly the height above sea level of a pressure level. For example, if a station reports that the 500 mb height at its location is 5600 m, it means that the level of the atmosphere over that station at which the atmospheric pressure is 500 mb is 5600 meters above sea level; this is an estimated height based on temperature and pressure data." Atmospheric model Above mean sea level Hofmann-Wellenhof, B. and Moritz, H.
"Physical Geodesy", 2005. ISBN 3-211-23584-1 Eskinazi, S. "Fluid Mechanics and Thermodynamics of our Environment", 1975. ISBN 0-12-242540-5 Media related to Geopotential height at Wikimedia Commons