Hydrazine is an inorganic compound with the chemical formula N2H4, called diamidogen, archaically. It is a simple pnictogen hydride, is a colorless and flammable liquid with an ammonia-like odour. Hydrazine is toxic and dangerously unstable unless handled in solution as e.g. hydrazine hydrate. As of 2015, the world hydrazine hydrate market amounted to $350 million. Hydrazine is used as a foaming agent in preparing polymer foams, but significant applications include its uses as a precursor to polymerization catalysts and agrochemicals. About two million tons of hydrazine hydrate were used in foam blowing agents in 2015. Additionally, hydrazine is used in various rocket fuels and to prepare the gas precursors used in air bags. Hydrazine is used within both nuclear and conventional electrical power plant steam cycles as an oxygen scavenger to control concentrations of dissolved oxygen in an effort to reduce corrosion. Hydrazines refer to a class of organic substances derived by replacing one or more hydrogen atoms in hydrazine by an organic group.
Each H2N−N subunit is pyramidal. The N−N single bond distance is 1.45 Å, the molecule adopts a gauche conformation. The rotational barrier is twice that of ethane; these structural properties resemble those of gaseous hydrogen peroxide, which adopts a "skewed" anticlinal conformation, experiences a strong rotational barrier. Diverse routes have been developed; the key step is the creation of the nitrogen–nitrogen single bond. The many routes can be divided into those that do not. Hydrazine can be synthesized from hydrogen peroxide in the Peroxide process; the net reaction follows: 2 NH 3 + H 2 O 2 ⟶ H 2 NNH 2 + 2 H 2 O In this route, the ketone and ammonia first condense to give the imine, oxidised by hydrogen peroxide to the oxaziridine, a three-membered ring containing carbon and nitrogen. Next, the oxaziridine gives the hydrazone by treatment with ammonia, which process creates the nitrogen-nitrogen single bond; this hydrazone condenses with one more equivalent of ketone. The resulting azine is hydrolyzed to give hydrazine and regenerate the ketone, methyl ethyl ketone: Me CNNC Me + 2 H 2 O ⟶ 2 Me CO + N 2 H 4 Unlike most other processes, this approach does not produce a salt as a by-product.
In the Olin Raschig process, chlorine-based oxidants oxidize ammonia without the presence of a ketone. In the peroxide process, hydrogen peroxide oxidizes ammonia in the presence of a ketone. Hydrazine is produced in the Olin-Raschig process from sodium hypochlorite and ammonia, a process announced in 1907; this method relies on the reaction of chloramine with ammonia to create the nitrogen–nitrogen single bond as well as a hydrogen chloride byproduct: NH 2 Cl + NH 3 ⟶ H 2 NNH 2 + HCl Related to the Raschig process, urea can be oxidized instead of ammonia. Again sodium hypochlorite serves as the oxidant; the net reaction is shown: 2 CO + NaOCl + 2 NaOH ⟶ N 2 H 4 + H 2 O + NaCl + Na 2 CO 3 The process generates significant byproducts and is practised in Asia. The Bayer Ketazine Process is the predecessor to the peroxide process, it employs sodium hypochlorite as oxidant instead of hydrogen peroxide. Like all hypochlorite-based routes, this method produces an equivalent of salt for each equivalent of hydrazine.
Hydrazine forms a monohydrate, more dense than the anhydrous material. Hydrazine has basic chemical properties comparable to those of ammonia, it is difficult to diprotonate: + + H 2 O ⟶ 2 + + OH − K b = 8.4 × 10 − 16 with the values: K b = 1.3 × 10 − 6 p K a = 8.1 (for ammon
In physics, an orbit is the gravitationally curved trajectory of an object, such as the trajectory of a planet around a star or a natural satellite around a planet. Orbit refers to a repeating trajectory, although it may refer to a non-repeating trajectory. To a close approximation and satellites follow elliptic orbits, with the central mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion. For most situations, orbital motion is adequately approximated by Newtonian mechanics, which explains gravity as a force obeying an inverse-square law. However, Albert Einstein's general theory of relativity, which accounts for gravity as due to curvature of spacetime, with orbits following geodesics, provides a more accurate calculation and understanding of the exact mechanics of orbital motion; the apparent motions of the planets were described by European and Arabic philosophers using the idea of celestial spheres. This model posited the existence of perfect moving spheres or rings to which the stars and planets were attached.
It assumed the heavens were fixed apart from the motion of the spheres, was developed without any understanding of gravity. After the planets' motions were more measured, theoretical mechanisms such as deferent and epicycles were added. Although the model was capable of reasonably predicting the planets' positions in the sky and more epicycles were required as the measurements became more accurate, hence the model became unwieldy. Geocentric it was modified by Copernicus to place the Sun at the centre to help simplify the model; the model was further challenged during the 16th century, as comets were observed traversing the spheres. The basis for the modern understanding of orbits was first formulated by Johannes Kepler whose results are summarised in his three laws of planetary motion. First, he found that the orbits of the planets in our Solar System are elliptical, not circular, as had been believed, that the Sun is not located at the center of the orbits, but rather at one focus. Second, he found that the orbital speed of each planet is not constant, as had been thought, but rather that the speed depends on the planet's distance from the Sun.
Third, Kepler found a universal relationship between the orbital properties of all the planets orbiting the Sun. For the planets, the cubes of their distances from the Sun are proportional to the squares of their orbital periods. Jupiter and Venus, for example, are about 5.2 and 0.723 AU distant from the Sun, their orbital periods about 11.86 and 0.615 years. The proportionality is seen by the fact that the ratio for Jupiter, 5.23/11.862, is equal to that for Venus, 0.7233/0.6152, in accord with the relationship. Idealised orbits meeting these rules are known as Kepler orbits. Isaac Newton demonstrated that Kepler's laws were derivable from his theory of gravitation and that, in general, the orbits of bodies subject to gravity were conic sections. Newton showed that, for a pair of bodies, the orbits' sizes are in inverse proportion to their masses, that those bodies orbit their common center of mass. Where one body is much more massive than the other, it is a convenient approximation to take the center of mass as coinciding with the center of the more massive body.
Advances in Newtonian mechanics were used to explore variations from the simple assumptions behind Kepler orbits, such as the perturbations due to other bodies, or the impact of spheroidal rather than spherical bodies. Lagrange developed a new approach to Newtonian mechanics emphasizing energy more than force, made progress on the three body problem, discovering the Lagrangian points. In a dramatic vindication of classical mechanics, in 1846 Urbain Le Verrier was able to predict the position of Neptune based on unexplained perturbations in the orbit of Uranus. Albert Einstein in his 1916 paper The Foundation of the General Theory of Relativity explained that gravity was due to curvature of space-time and removed Newton's assumption that changes propagate instantaneously; this led astronomers to recognize that Newtonian mechanics did not provide the highest accuracy in understanding orbits. In relativity theory, orbits follow geodesic trajectories which are approximated well by the Newtonian predictions but the differences are measurable.
All the experimental evidence that can distinguish between the theories agrees with relativity theory to within experimental measurement accuracy. The original vindication of general relativity is that it was able to account for the remaining unexplained amount in precession of Mercury's perihelion first noted by Le Verrier. However, Newton's solution is still used for most short term purposes since it is easier to use and sufficiently accurate. Within a planetary system, dwarf planets and other minor planets and space debris orbit the system's barycenter in elliptical orbits. A comet in a parabolic or hyperbolic orbit about a barycenter is not gravitationally bound to the star and therefore is not considered part of the star's planetary system. Bodies which are gravitationally bound to one of the planets in a planetary system, either natural or artificial satellites, follow orbits about a barycenter near or within that planet. Owing to mutual gravitational perturbations, the eccentricities of the planetary orbits vary over time.
Mercury, the smallest planet in the Solar System, has the most eccentric orbit
Hydrogen peroxide is a chemical compound with the formula H2O2. In its pure form, it is a pale blue, clear liquid more viscous than water. Hydrogen peroxide is the simplest peroxide, it is used as bleaching agent and antiseptic. Concentrated hydrogen peroxide, or "high-test peroxide", is a reactive oxygen species and has been used as a propellant in rocketry, its chemistry is dominated by the nature of its unstable peroxide bond. Hydrogen peroxide is unstable and decomposes in the presence of light; because of its instability, hydrogen peroxide is stored with a stabilizer in a weakly acidic solution. Hydrogen peroxide is found in biological systems including the human body. Enzymes that use or decompose hydrogen peroxide are classified as peroxidases; the boiling point of H2O2 has been extrapolated as being 150.2 °C 50 °C higher than water. In practice, hydrogen peroxide will undergo explosive thermal decomposition if heated to this temperature, it may be safely distilled at lower temperatures under reduced pressure.
In aqueous solutions hydrogen peroxide differs from the pure substance due to the effects of hydrogen bonding between water and hydrogen peroxide molecules. Hydrogen peroxide and water form a eutectic mixture; the boiling point of the same mixtures is depressed in relation with the mean of both boiling points. It occurs at 114 °C; this boiling point is 14 °C greater than that of pure water and 36.2 °C less than that of pure hydrogen peroxide. Hydrogen peroxide is a nonplanar molecule as shown by Paul-Antoine Giguère in 1950 using infrared spectroscopy, with C2 symmetry. Although the O−O bond is a single bond, the molecule has a high rotational barrier of 2460 cm−1; the increased barrier is ascribed to repulsion between the lone pairs of the adjacent oxygen atoms and results in hydrogen peroxide displaying atropisomerism. The molecular structures of gaseous and crystalline H2O2 are different; this difference is attributed to the effects of hydrogen bonding, absent in the gaseous state. Crystals of H2O2 are tetragonal with the space group D44P4121.
Hydrogen peroxide has several structural analogues with Hm−X−X−Hn bonding arrangements. It has the highest boiling point of this series, its melting point is fairly high, being comparable to that of hydrazine and water, with only hydroxylamine crystallising more indicative of strong hydrogen bonding. Diphosphane and hydrogen disulfide exhibit only weak hydrogen bonding and have little chemical similarity to hydrogen peroxide. All of these analogues are thermodynamically unstable. Structurally, the analogues all adopt similar skewed structures, due to repulsion between adjacent lone pairs. Alexander von Humboldt synthesized one of the first synthetic peroxides, barium peroxide, in 1799 as a by-product of his attempts to decompose air. Nineteen years Louis Jacques Thénard recognized that this compound could be used for the preparation of a unknown compound, which he described as eau oxygénée – subsequently known as hydrogen peroxide. An improved version of Thénard's process used hydrochloric acid, followed by addition of sulfuric acid to precipitate the barium sulfate byproduct.
This process was used from the end of the 19th century until the middle of the 20th century. Thénard and Joseph Louis Gay-Lussac synthesized sodium peroxide in 1811; the bleaching effect of peroxides and their salts on natural dyes became known around that time, but early attempts of industrial production of peroxides failed, the first plant producing hydrogen peroxide was built in 1873 in Berlin. The discovery of the synthesis of hydrogen peroxide by electrolysis with sulfuric acid introduced the more efficient electrochemical method, it was first implemented into industry in 1908 in Weißenstein, Austria. The anthraquinone process, still used, was developed during the 1930s by the German chemical manufacturer IG Farben in Ludwigshafen; the increased demand and improvements in the synthesis methods resulted in the rise of the annual production of hydrogen peroxide from 35,000 tonnes in 1950, to over 100,000 tonnes in 1960, to 300,000 tonnes by 1970. Pure hydrogen peroxide was long believed to be unstable, as early attempts to separate it from the water, present during synthesis, all failed.
This instability was due to traces of impurities, which catalyze the decomposition of the hydrogen peroxide. Pure hydrogen peroxide was first obtained in 1894—almost 80 years after its discovery—by Richard Wolffenstein, who produced it by vacuum distillation. Determination of the molecular structure of hydrogen peroxide proved to be difficult. In 1892 the Italian physical chemist Giacomo Carrara determined its molecular mass by freezing-point depression, which confirmed that its molecular formula is H2O2. At least half a dozen hypothetical molecular structures seemed to be consistent with the available evidence. In 1934, the English mathematical physicist William Penney and the Scottish physicist Gordon Sutherland proposed a molecular structure for hydrogen peroxide, similar to the presently accepted one. Hydrogen peroxide was prepared industrially by hydrolysis of ammonium persulfate, itself obtained by the electrolysis of a solution
Monomethylhydrazine is a volatile hydrazine chemical with the chemical formula CH3NH2. It is used as a rocket propellant in bipropellant rocket engines because it is hypergolic with various oxidizers such as nitrogen tetroxide and nitric acid; as a propellant, it is described in specification MIL-PRF-27404. MMH is a hydrazine derivative, once used in the orbital maneuvering system and reaction control system engines of NASA's Space Shuttle, which used MMH and MON-3; this chemical is toxic and carcinogenic in small amounts, but it is stored in orbit providing moderate performance for low fuel tank system weight. The European Space Agency has attempted to seek new options in terms of bipropellant rocket combinations to avoid poisonous chemicals such as this and its relatives. MMH and its chemical relative unsymmetrical dimethylhydrazine have a key advantage that they are stable enough to be used in regeneratively cooled rocket engines; the Apollo Lunar Modules used a one-to-one mixture of hydrazine and UDMH as one part of the rocket fuel for lunar landings and takeoff: the rocket motors formed a hypergolic mixture of the hydrazines with liquid dinitrogen tetroxide as the usual oxidizer.
About three tons of mixed hydrazines and four and one half tons of the oxidizer were required for each landing, about one-third of those amounts for the lunar take-off to orbit. Monomethylhydrazine is believed to be the main cause of the toxicity of mushrooms of genus Gyromitra the false morel. In these cases, MMH is formed by the hydrolysis of gyromitrin. Monomethylhydrazine is considered to be a possible occupational carcinogen, the occupational exposure limits to MMH are set at protective levels to account for the possible carcinogenicity. A known use of MMH is in the synthesis of Suritozole
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. Space propulsion or in-space propulsion deals with propulsion systems used in the vacuum of space and should not be confused with launch vehicles. Several methods, both pragmatic and hypothetical, have been developed each having its own drawbacks and advantages. Most satellites have simple reliable chemical thrusters or resistojet rockets for orbital station-keeping and some use momentum wheels for attitude control. Soviet bloc satellites have used electric propulsion for decades, newer Western geo-orbiting spacecraft are starting to use them for north-south station-keeping and orbit raising. Interplanetary vehicles use chemical rockets as well, although a few have used Ion thrusters and Hall effect thrusters to great success. Artificial satellites must be launched into orbit after which they must be placed in their nominal orbit. Once in the desired orbit, they need some form of attitude control so that they are pointed with respect to the Earth, the Sun, some astronomical object of interest.
They are subject to drag from the thin atmosphere, so that to stay in orbit for a long period of time some form of propulsion is necessary to make small corrections. Many satellites need to be moved from one orbit to another from time to time, this requires propulsion. A satellite's useful life is over once it has exhausted its ability to adjust its orbit. For interplanetary travel, a spacecraft must use its engines to leave Earth's orbit. Once it has done so, it must somehow make its way to its destination. Current interplanetary spacecraft do this with a series of short-term trajectory adjustments. In between these adjustments, the spacecraft moves along its trajectory with a constant velocity; the most fuel-efficient means to move from one circular orbit to another is with a Hohmann transfer orbit: the spacecraft begins in a circular orbit around the Sun. A short period of thrust in the direction of motion accelerates or decelerates the spacecraft into an elliptical orbit around the Sun, tangential to its previous orbit and to the orbit of its destination.
The spacecraft falls along this elliptical orbit until it reaches its destination, where another short period of thrust accelerates or decelerates it to match the orbit of its destination. Special methods such as aerobraking or aerocapture are sometimes used for this final orbital adjustment; some spacecraft propulsion methods such as solar sails provide low but inexhaustible thrust. The concept has been tested by the Japanese IKAROS solar sail spacecraft. No spacecraft capable of short duration interstellar travel has yet been built, but many hypothetical designs have been discussed; because interstellar distances are great, a tremendous velocity is needed to get a spacecraft to its destination in a reasonable amount of time. Acquiring such a velocity on launch and getting rid of it on arrival remains a formidable challenge for spacecraft designers; when in space, the purpose of a propulsion system is to change the v, of a spacecraft. Because this is more difficult for more massive spacecrafts, designers discuss spacecraft performance in amount of change in momentum per unit of propellant consumed called specific impulse.
Higher the specific impulse, better the efficiency. Ion propulsion engines have high specific impulse and low thrust whereas chemical rockets like monopropellant or bipropellant rocket engines have a low specific impulse but high thrust; when launching a spacecraft from Earth, a propulsion method must overcome a higher gravitational pull to provide a positive net acceleration. In orbit, any additional impulse very tiny, will result in a change in the orbit path; the rate of change of velocity is called acceleration, the rate of change of momentum is called force. To reach a given velocity, one can apply a small acceleration over a long period of time, or one can apply a large acceleration over a short time. One can achieve a given impulse with a large force over a short time or a small force over a long time; this means that for manoeuvring in space, a propulsion method that produces tiny accelerations but runs for a long time can produce the same impulse as a propulsion method that produces large accelerations for a short time.
When launching from a planet, tiny accelerations cannot overcome the planet's gravitational pull and so cannot be used. Earth's surface is situated deep in a gravity well; the escape velocity required to get out of it is 11.2 kilometers/second. As human beings evolved in a gravitational field of 1g, an ideal propulsion system would be one that provides a continuous acceleration of 1g; the occupants of a rocket or spaceship having such a propulsion system would be free from all the ill effects of free fall, such as nausea, muscular weakness, reduced sense of taste, or leaching of calcium from their bones. The law of conservation of momentum means that in order for a propulsion method to change the momentum of a space craft it must change the momentum of something else as well. A few designs take advantage of things like magnetic fields or light pressure in order to chan