In physics the Lorentz force is the combination of electric and magnetic force on a point charge due to electromagnetic fields. A particle of charge q moving with a velocity v in an electric field E and a magnetic field B experiences a force of F = q E + q v × B. Variations on this basic formula describe the magnetic force on a current-carrying wire, the electromotive force in a wire loop moving through a magnetic field, the force on a charged particle which might be traveling near the speed of light. Historians suggest that the law is implicit in a paper by James Clerk Maxwell, published in 1865. Hendrik Lorentz arrived in a complete derivation in 1895, identifying the contribution of the electric force a few years after Oliver Heaviside identified the contribution of the magnetic force; the force F acting on a particle of electric charge q with instantaneous velocity v, due to an external electric field E and magnetic field B, is given by: where × is the vector cross product. In terms of cartesian components, we have: F x = q, F y = q, F z = q.
In general, the electric and magnetic fields are functions of the time. Therefore, the Lorentz force can be written as: F = q in which r is the position vector of the charged particle, t is time, the overdot is a time derivative. A positively charged particle will be accelerated in the same linear orientation as the E field, but will curve perpendicularly to both the instantaneous velocity vector v and the B field according to the right-hand rule; the term qE is called the electric force. According to some definitions, the term "Lorentz force" refers to the formula for the magnetic force, with the total electromagnetic force given some other name; this article will not follow this nomenclature: In what follows, the term "Lorentz force" will refer to the expression for the total force. The magnetic force component of the Lorentz force manifests itself as the force that acts on a current-carrying wire in a magnetic field. In that context, it is called the Laplace force; the Lorentz force is a force exerted by the electromagnetic field on the charged particle, that is, it is the rate at which linear momentum is transferred from the electromagnetic field to the particle.
Associated with it is the power, the rate at which energy is transferred from the electromagnetic field to the particle. That power is v ⋅ F = q v ⋅ E. Notice that the magnetic field does not contribute to the power because the magnetic force is always perpendicular to the velocity of the particle. For a continuous charge distribution in motion, the Lorentz force equation becomes: d F = d q where dF is the force on a small piece of the charge distribution with charge dq. If both sides of this equation are divided by the volume of this small piece of the charge distribution dV, the result is: f = ρ where f is the force density and ρ is the charge density. Next, the current density corresponding to the motion of the charge continuum is J = ρ v so the continuous analogue to the equation is The total force is the volume integral over the charge distr
Sublimation (phase transition)
Sublimation is the transition of a substance directly from the solid to the gas phase, without passing through the intermediate liquid phase. Sublimation is an endothermic process that occurs at temperatures and pressures below a substance's triple point in its phase diagram, which corresponds to the lowest pressure at which the substance can exist as a liquid; the reverse process of sublimation is deposition or desublimation, in which a substance passes directly from a gas to a solid phase. Sublimation has been used as a generic term to describe a solid-to-gas transition followed by a gas-to-solid transition. While a transition from liquid to gas is described as evaporation if it occurs below the boiling point of the liquid, as boiling if it occurs at the boiling point, there is no such distinction within the solid-to-gas transition, always described as sublimation. At normal pressures, most chemical compounds and elements possess three different states at different temperatures. In these cases, the transition from the solid to the gaseous state requires an intermediate liquid state.
The pressure referred to is the partial pressure of the substance, not the total pressure of the entire system. So, all solids that possess an appreciable vapour pressure at a certain temperature can sublime in air. For some substances, such as carbon and arsenic, sublimation is much easier than evaporation from the melt, because the pressure of their triple point is high, it is difficult to obtain them as liquids; the term sublimation refers to a physical change of state and is not used to describe the transformation of a solid to a gas in a chemical reaction. For example, the dissociation on heating of solid ammonium chloride into hydrogen chloride and ammonia is not sublimation but a chemical reaction; the combustion of candles, containing paraffin wax, to carbon dioxide and water vapor is not sublimation but a chemical reaction with oxygen. Sublimation is caused by the absorption of heat which provides enough energy for some molecules to overcome the attractive forces of their neighbors and escape into the vapor phase.
Since the process requires additional energy, it is an endothermic change. The enthalpy of sublimation can be calculated by adding the enthalpy of fusion and the enthalpy of vaporization. Solid carbon dioxide sublimes everywhere along the line below the triple point (e.g. at the temperature of −78.5 °C at atmospheric pressure, whereas its melting into liquid CO2 can occur only along the line at pressures and temperatures above the triple point. Snow and ice sublime, although more at temperatures below the freezing/melting point temperature line at 0 °C for most pressures. In freeze-drying, the material to be dehydrated is frozen and its water is allowed to sublime under reduced pressure or vacuum; the loss of snow from a snowfield during a cold spell is caused by sunshine acting directly on the upper layers of the snow. Ablation is a process that includes erosive wear of glacier ice. Naphthalene, an organic compound found in pesticides such as mothballs, sublimes because it is made of non-polar molecules that are held together only by van der Waals intermolecular forces.
Naphthalene is a solid that sublimes at standard atmospheric temperature with the sublimation point at around 80 °C or 176 °F. At low temperature, its vapour pressure is high enough, 1 mmHg at 53 °C, to make the solid form of naphthalene evaporate into gas. On cool surfaces, the naphthalene vapours will solidify to form needle-like crystals. Iodine produces fumes on gentle heating, it is possible to obtain liquid iodine at atmospheric pressure by controlling the temperature at just above the melting point of iodine. In forensic science, iodine vapor can reveal latent fingerprints on paper. Arsenic can sublime at high temperatures. Cadmium and zinc are not suitable materials for use in vacuum because they sublimate much more than other common materials. Sublimation is a technique used by chemists to purify compounds. A solid is placed in a sublimation apparatus and heated under vacuum. Under this reduced pressure, the solid volatilizes and condenses as a purified compound on a cooled surface, leaving a non-volatile residue of impurities behind.
Once heating ceases and the vacuum is removed, the purified compound may be collected from the cooling surface. For higher purification efficiencies, a temperature gradient is applied, which allows for the separation of different fractions. Typical setups use an evacuated glass tube, heated in a controlled manner; the material flow is from the hot end, where the initial material is placed, to the cold end, connected to a pump stand. By controlling temperatures along the length of the tube, the operator can control the zones of re-condensation, with volatile compounds being pumped out of the system moderately volatile compounds re-condensing along the tube according to their different volatilities, non-volatile compounds remaining in the hot end. Vacuum sublimation of this type is the method of choice for purification of organic compounds for use in the organic electronics industry, where high purities are needed to satisfy the standards for consumer electronics and other applications. In ancient alchemy, a protoscience that contributed to the development of modern chemistry and medicine, alchemists developed a structure of basic laboratory techniques, theory and experimental methods.
Sublimation was used to refer to the process in which a
Plasma is one of the four fundamental states of matter, was first described by chemist Irving Langmuir in the 1920s. Plasma can be artificially generated by heating or subjecting a neutral gas to a strong electromagnetic field to the point where an ionized gaseous substance becomes electrically conductive, long-range electromagnetic fields dominate the behaviour of the matter. Plasma and ionized gases have properties and display behaviours unlike those of the other states, the transition between them is a matter of nomenclature and subject to interpretation. Based on the surrounding environmental temperature and density ionized or ionized forms of plasma may be produced. Neon signs and lightning are examples of ionized plasma; the Earth's ionosphere is a plasma and the magnetosphere contains plasma in the Earth's surrounding space environment. The interior of the Sun is an example of ionized plasma, along with the solar corona and stars. Positive charges in ions are achieved by stripping away electrons orbiting the atomic nuclei, where the total number of electrons removed is related to either increasing temperature or the local density of other ionized matter.
This can be accompanied by the dissociation of molecular bonds, though this process is distinctly different from chemical processes of ion interactions in liquids or the behaviour of shared ions in metals. The response of plasma to electromagnetic fields is used in many modern technological devices, such as plasma televisions or plasma etching. Plasma may be the most abundant form of ordinary matter in the universe, although this hypothesis is tentative based on the existence and unknown properties of dark matter. Plasma is associated with stars, extending to the rarefied intracluster medium and the intergalactic regions; the word plasma comes from Ancient Greek πλάσμα, meaning'moldable substance' or'jelly', describes the behaviour of the ionized atomic nuclei and the electrons within the surrounding region of the plasma. Each of these nuclei are suspended in a movable sea of electrons. Plasma was first identified in a Crookes tube, so described by Sir William Crookes in 1879; the nature of this "cathode ray" matter was subsequently identified by British physicist Sir J.
J. Thomson in 1897; the term "plasma" was coined by Irving Langmuir in 1928. Lewi Tonks and Harold Mott-Smith, both of whom worked with Irving Langmuir in the 1920s, recall that Langmuir first used the word "plasma" in analogy with blood. Mott-Smith recalls, in particular, that the transport of electrons from thermionic filaments reminded Langmuir of "the way blood plasma carries red and white corpuscles and germs."Langmuir described the plasma he observed as follows: "Except near the electrodes, where there are sheaths containing few electrons, the ionized gas contains ions and electrons in about equal numbers so that the resultant space charge is small. We shall use the name plasma to describe this region containing balanced charges of ions and electrons." Plasma is a state of matter in which an ionized gaseous substance becomes electrically conductive to the point that long-range electric and magnetic fields dominate the behaviour of the matter. The plasma state can be contrasted with the other states: solid and gas.
Plasma is an electrically neutral medium of unbound negative particles. Although these particles are unbound, they are not "free" in the sense of not experiencing forces. Moving charged particles generate an electric current within a magnetic field, any movement of a charged plasma particle affects and is affected by the fields created by the other charges. In turn this governs collective behaviour with many degrees of variation. Three factors define a plasma: The plasma approximation: The plasma approximation applies when the plasma parameter, Λ, representing the number of charge carriers within a sphere surrounding a given charged particle, is sufficiently high as to shield the electrostatic influence of the particle outside of the sphere. Bulk interactions: The Debye screening length is short compared to the physical size of the plasma; this criterion means that interactions in the bulk of the plasma are more important than those at its edges, where boundary effects may take place. When this criterion is satisfied, the plasma is quasineutral.
Plasma frequency: The electron plasma frequency is large compared to the electron-neutral collision frequency. When this condition is valid, electrostatic interactions dominate over the processes of ordinary gas kinetics. Plasma temperature is measured in kelvin or electronvolts and is, informally, a measure of the thermal kinetic energy per particle. High temperatures are needed to sustain ionisation, a defining feature of a plasma; the degree of plasma ionisation is determined by the electron temperature relative to the ionization energy, in a relationship called the Saha equation. At low temperatures and electrons tend to recombine into bound states—atoms—and the plasma will become a gas. In most cases the electrons are close enough to thermal equilibrium that their temperature is well-defined; because of the large difference in ma
The National Aeronautics and Space Administration is an independent agency of the United States Federal Government responsible for the civilian space program, as well as aeronautics and aerospace research. NASA was established in 1958; the new agency was to have a distinctly civilian orientation, encouraging peaceful applications in space science. Since its establishment, most US space exploration efforts have been led by NASA, including the Apollo Moon landing missions, the Skylab space station, the Space Shuttle. NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle, the Space Launch System and Commercial Crew vehicles; the agency is responsible for the Launch Services Program which provides oversight of launch operations and countdown management for unmanned NASA launches. NASA science is focused on better understanding Earth through the Earth Observing System. From 1946, the National Advisory Committee for Aeronautics had been experimenting with rocket planes such as the supersonic Bell X-1.
In the early 1950s, there was challenge to launch an artificial satellite for the International Geophysical Year. An effort for this was the American Project Vanguard. After the Soviet launch of the world's first artificial satellite on October 4, 1957, the attention of the United States turned toward its own fledgling space efforts; the US Congress, alarmed by the perceived threat to national security and technological leadership, urged immediate and swift action. On January 12, 1958, NACA organized a "Special Committee on Space Technology", headed by Guyford Stever. On January 14, 1958, NACA Director Hugh Dryden published "A National Research Program for Space Technology" stating: It is of great urgency and importance to our country both from consideration of our prestige as a nation as well as military necessity that this challenge be met by an energetic program of research and development for the conquest of space... It is accordingly proposed that the scientific research be the responsibility of a national civilian agency...
NACA is capable, by rapid extension and expansion of its effort, of providing leadership in space technology. While this new federal agency would conduct all non-military space activity, the Advanced Research Projects Agency was created in February 1958 to develop space technology for military application. On July 29, 1958, Eisenhower signed the National Aeronautics and Space Act, establishing NASA; when it began operations on October 1, 1958, NASA absorbed the 43-year-old NACA intact. A NASA seal was approved by President Eisenhower in 1959. Elements of the Army Ballistic Missile Agency and the United States Naval Research Laboratory were incorporated into NASA. A significant contributor to NASA's entry into the Space Race with the Soviet Union was the technology from the German rocket program led by Wernher von Braun, now working for the Army Ballistic Missile Agency, which in turn incorporated the technology of American scientist Robert Goddard's earlier works. Earlier research efforts within the US Air Force and many of ARPA's early space programs were transferred to NASA.
In December 1958, NASA gained control of the Jet Propulsion Laboratory, a contractor facility operated by the California Institute of Technology. The agency's leader, NASA's administrator, is nominated by the President of the United States subject to approval of the US Senate, reports to him or her and serves as senior space science advisor. Though space exploration is ostensibly non-partisan, the appointee is associated with the President's political party, a new administrator is chosen when the Presidency changes parties; the only exceptions to this have been: Democrat Thomas O. Paine, acting administrator under Democrat Lyndon B. Johnson, stayed on while Republican Richard Nixon tried but failed to get one of his own choices to accept the job. Paine was confirmed by the Senate in March 1969 and served through September 1970. Republican James C. Fletcher, appointed by Nixon and confirmed in April 1971, stayed through May 1977 into the term of Democrat Jimmy Carter. Daniel Goldin was appointed by Republican George H. W. Bush and stayed through the entire administration of Democrat Bill Clinton.
Robert M. Lightfoot, Jr. associate administrator under Democrat Barack Obama, was kept on as acting administrator by Republican Donald Trump until Trump's own choice Jim Bridenstine, was confirmed in April 2018. Though the agency is independent, the survival or discontinuation of projects can depend directly on the will of the President; the first administrator was Dr. T. Keith Glennan appointed by Republican President Dwight D. Eisenhower. During his term he brought together the disparate projects in American space development research; the second administrator, James E. Webb, appointed by President John F. Kennedy, was a Democrat who first publicly served under President Harry S. Truman. In order to implement the Apollo program to achieve Kennedy's Moon la
Staged combustion cycle
The staged combustion cycle is a power cycle of a bipropellant rocket engine. In the staged combustion cycle, propellant flows through multiple combustion chambers, is thus combusted in stages; the main advantage relative to other rocket engine power cycles is high fuel efficiency, measured through specific impulse, while its main disadvantage is engineering complexity. Propellant flows through two kinds of combustion chambers. In the preburner, a small portion of propellant is combusted, the over-pressure produced is used to drive the turbopumps that feed the engine with propellant. In the main combustion chamber, the propellants are combusted to produce thrust; the fuel efficiency of the staged combustion cycle is in part a result of all propellant flowing to the main combustion chamber. The staged combustion cycle is sometimes referred to as closed cycle, as opposed to the gas generator, or open cycle where a portion of propellant never reaches the main combustion chamber; the engineering complexity is a result of the preburner exhaust of hot and pressurized gas which when oxidizer-rich, produces harsh conditions for turbines and plumbing.
Staged combustion was first proposed by Alexey Isaev in 1949. The first staged combustion engine was the S1.5400 used in the Soviet planetary rocket, designed by Melnikov, a former assistant to Isaev. About the same time, Nikolai Kuznetsov began work on the closed cycle engine NK-9 for Korolev's orbital ICBM, GR-1. Kuznetsov evolved that design into the NK-15 and NK-33 engines for the unsuccessful Lunar N1 rocket; the non-cryogenic N2O4/UDMH engine RD-253 using staged combustion was developed by Valentin Glushko circa 1963 for the Proton rocket. After the abandonment of the N-1, Kuznetsov was ordered to destroy the NK-33 technology, but instead he warehoused dozens of the engines. In the 1990s, Aerojet was contacted and visited Kuznetsov's plant. Upon meeting initial skepticism about the high specific impulse and other specifications, Kuznetsov shipped an engine to the US for testing. Oxidizer-rich staged combustion had been deemed impossible; the Russian RD-180 engine employs a staged-combustion rocket engine cycle.
Lockheed Martin began purchasing the RD-180 in circa 2000 for the Atlas III and the V, rockets. The purchase contract was subsequently taken over by United Launch Alliance, the Lockheed-Martin successor company after 2006, ULA continues to fly the Atlas V with RD-180 engines as of 2019; the first laboratory staged-combustion test engine in the West was built in Germany in 1963, by Ludwig Boelkow. Hydrogen peroxide/kerosene fueled engines such as the British Gamma of the 1950s may use a closed-cycle process by catalytically decomposing the peroxide to drive turbines before combustion with the kerosene in the combustion chamber proper; this gives the efficiency advantages of staged combustion, while avoiding major engineering problems. The Space Shuttle Main Engine is another example of a staged combustion engine, the first to use liquid oxygen and liquid hydrogen, its counterpart in the Soviet shuttle was the RD-0120, similar in specific impulse and chamber pressure specification to the SSME, but with some differences that reduced complexity and cost at the expense of increased engine weight.
Several variants of the staged combustion cycle exist. Preburners that burn a small portion of oxidizer with a full flow of fuel are called fuel-rich, while preburners that burn a small portion of fuel with a full flow of oxidizer are called oxidizer-rich; the RD-180 has an oxidizer-rich preburner. The SpaceX Raptor has both oxidizer-rich and fuel-rich preburners, a design called full-flow staged combustion. Staged combustion designs can be either twin-shaft. In the single-shaft design, one set of preburner and turbine drives both propellant turbopumps. Examples include the Energomash RD-180 and the Blue Origin BE-4. In the twin-shaft design, the two propellant turbopumps are driven by separate turbines, which are in turn driven by the outflow of either one or separate preburners. Examples of twin-shaft designs include the Rocketdyne RS-25, the JAXA LE-7, the Raptor. Relative to a single-shaft design, the twin-shaft design requires an additional turbine, but allows for individual control of the two turbopumps.
In addition to the propellant turbopumps, staged combustion engines require smaller boost pumps so to prevent both preburner backflow and turbopump cavitation. For example, the RD-180 and RS-25 use boost pumps driven by tap-off and expander cycles, as well as pressurized tanks, to incrementally increase propellant pressure prior to entering the preburner. Full-flow staged combustion is a twin-shaft staged combustion cycle that uses both oxidizer-rich and fuel-rich preburners; the cycle allows full flow of both propellants through the turbines. The fuel turbopump is driven by the fuel-rich preburner, the oxidizer turbopump is driven by the oxidizer-rich preburner. Benefits of the full-flow staged combustion cycle include turbines that run cooler and at lower pressure, due to increased mass flow, leading to a longer engine life and higher reliability; as an example, up to 25 flights were anticipated for an engine design studied by the DLR in the frame of the SpaceLiner project. Further, the full-flow cycle eliminates the need for an interpropellant turbine seal required to separate oxidizer-rich gas from the fuel turbopump or fuel-
A hybrid-propellant rocket is a rocket with a rocket motor that uses rocket propellants in two different phases: one solid and the other either gas or liquid. The hybrid rocket concept can be traced back at least 75 years. Hybrid rockets avoid some of the disadvantages of solid rockets like the dangers of propellant handling, while avoiding some disadvantages of liquid rockets like their mechanical complexity; because it is difficult for the fuel and oxidizer to be mixed intimately, hybrid rockets tend to fail more benignly than liquids or solids. Like liquid rocket engines, hybrid rocket motors can be shut down and the thrust is throttleable; the theoretical specific impulse performance of hybrids is higher than solid motors and lower than liquid engines. I s p as high. Hybrid systems are more complex than solid ones, but they avoid significant hazards of manufacturing and handling solid rocket motors by storing the oxidizer and the fuel separately; the first work on hybrid rockets was performed in the late 1930s at IG Farben in Germany and concurrently at the California Rocket Society in the United States.
Leonid Andrussow, working in Germany, first theorized hybrid propellant rockets. O. Lutz, W. Noeggerath, Andrussow tested a 10 kilonewtons hybrid rocket motor using coal and gaseous N2O as the propellants. Oberth worked on a hybrid rocket motor using LOX as the oxidizer and graphite as the fuel; the high heat of sublimation of carbon prevented these rocket motors from operating efficiently, as it resulted in a negligible burning rate. In the 1940s, the California Pacific Rocket Society used LOX in combination with several different fuel types, including wood and rubber; the most successful of these tests was with the rubber fuel, still the dominant fuel in use today. In June 1951, a LOX/rubber rocket was flown to an altitude of 9 kilometres. Two major efforts occurred in the 1950s. One of these efforts was by K. Berman at General Electric; the duo used 90 % polyethylene in a rod and tube grain design. They drew several significant conclusions from their work; the fuel grain had uniform burning. Grain cracks did not affect combustion.
No hard starts were observed. The fuel surface acted as a flame holder; the oxidizer could be throttled with one valve, a high oxidizer to fuel ratio helped simplify combustion. The negative observations were low burning rates and that the thermal instability of peroxide was problematic for safety reasons. Another effort that occurred in the 1950s was development of a reverse hybrid. In a standard hybrid rocket motor, the solid material is the fuel. In a reverse hybrid rocket motor, the oxidizer is solid. William Avery of the Applied Physics Laboratory used jet fuel and ammonium nitrate, selected for their low cost, his O/F ratio was 0.035, 200 times smaller than the ratio used by Moore and Berman. In 1953 Pacific Rocket Society was developing the XDF-23, a 4 inches x 72 inches hybrid rocket, designed by Jim Nuding, using LOX and rubber polymer called "Thiokol", they had tried other fuels in prior iterations including cotton, paraffin wax and wood. The XDF name. In the 1960s, European organizations began work on hybrid rockets.
ONERA, based in France, Volvo Flygmotor, based in Sweden, developed sounding rockets using hybrid rocket motor technology. The ONERA group focused on a hypergolic rocket motor, using an amine fuel; the company flew eight rockets: once in April 1964, three times in June 1965, four times in 1967. The maximum altitude the flights achieved was over 100 kilometres; the Volvo Flygmotor group used a hypergolic propellant combination. They used nitric acid for their oxidizer, but used Tagaform as their fuel, their flight was in 1969. Meanwhile, in the United States, United Technologies Center and Beech Aircraft were working on a supersonic target drone, known as Sandpiper, it used polymethyl methacrylate - Mg for the fuel. The drone flew six times in 1968, for more than 300 seconds and to an altitude greater than 160 kilometres; the second iteration of the rocket, known as the HAST, had IRFNA-PB/PMM for its propellants and was throttleable over a 10/1 range. HAST could carry a heavier payload than the Sandpiper.
Another iteration, which used the same propellant combination as the HAST, was developed by Chemical Systems Division and Teledyne Aircraft. Development for this program ended in the mid-1980s. Chemical Systems Division worked on a propellant combination of lithium and FLOx; this was an efficient hypergolic rocket, throtteable. The vacuum specific impulse was 380 seconds at 93% combustion efficiency. AMROC developed the largest hybrid rockets created in the late 1980s and early 1990s; the first version of their engine, fired at the Air Force Phillips Laboratory, produced 312,000 newtons of thrust for 70 seconds with a propellant combination of LOX and hydroxyl-terminated polybutadiene. The second version of the motor, known as the H-250F, produced more than 1,000,000 newtons o