Rocket propellant

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Rocket propellant is the material used either directly by the rocket as the reaction mass (mass of propulsion) issued, usually at a very high speed, from a rocket engine to generate a boost, and thus provides a spacecraft propulsion, or indirectly to produce reaction mass in chemical reactions. Each type of rocket requires a different type of propellant: a chemical rocket requires a propellant capable of undergoing an exothermic chemical reaction, which provides the energy to accelerate the gas produced through the nozzle. Thermal rockets instead use inert propellants of low molecular weight that are chemically compatible with the heating mechanism at high temperatures, while cold gas promoters use pressurized inert gas, easily stored. Electric propulsion forces require propellant to be easily ionized or made into plasma, and in extreme cases propellant nuclear pulse propulsion consists of many small, non-nuclear explosive weapons in which the resulting shock waves push the spacecraft away from the explosive, thus creating a propulsion. One of the spacecraft was designed (but never built), dubbed the "Orion Project" (not to be confused with the NASA Orion spacecraft).

Video Rocket propellant

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Rocket propellants are high oxygen-containing fuels or fuel mixtures plus oxidants, whose combustion takes place, in a definite and controlled manner with the evolution of very large volumes of gas. In a rocket engine, the propellant is burned in the combustion chamber and the hot gas jet (usually at 3000 ° C and 300 kg/cm 2) passes through the nozzle at a very high speed. The rocket creates a boost by repelling the mass in high speed jets (see Third Newton's Law). The chemical rocket, the subject of this article, creates a boost by reacting the propellant inside the combustion chamber into a very hot gas at high pressure, which is then expanded and accelerated by way through the nozzle at the rear of the rocket. The amount of the resulting forward force, known as thrust, is the propellant mass flow rate multiplied by its velocity (relative to the rocket), as determined by Newton's third law of motion. The impulse is, therefore, the same and opposite reaction that drives the rocket, and not by the interaction of the exhaust flow with the air around the rocket. Equivalently, one can think of rockets being accelerated upward by the pressure of flaming gases against the combustion chamber and the nozzle. This operational principle is in stark contrast to the common belief that rockets "push" against the air behind or below it. Rockets actually perform better in outer space (where there is no behind or below them to push), because there is a reduction in air pressure on the outside of the engine, and because it is possible to install longer nozzles without suffering flow separation, in addition to the lack of resistance air.

Kecepatan maksimum yang dapat dicapai oleh roket tanpa adanya kekuatan eksternal terutama adalah fungsi dari rasio massanya dan kecepatan buangnya . Hubungan ini dijelaskan oleh persamaan rocket : ${\ displaystyle V_ {f} = V_ {e} \ ln (M_ {0}/M_ {f})}  ÂÂ$ , di mana ${\ displaystyle V_ {f}}  ÂÂ$ adalah kecepatan akhir, ${\ displaystyle V_ {e}}  ÂÂ$ adalah kecepatan buang relatif terhadap roket, ${\ displaystyle M_ {0}}  ÂÂ$ adalah total massa awal, dan ${\ displaystyle M_ {f}}  ÂÂ$ adalah massa setelah propelan dibakar. Rasio massa menyatakan berapa proporsi roket adalah propelan (kombinasi bahan bakar/pengoksidasi) sebelum pengapian mesin. Biasanya, roket satu tahap mungkin memiliki fraksi massa propelan 90%, struktur 10%, dan karenanya rasio massa 9: 1. Dorongan yang disampaikan oleh motor ke kendaraan roket per berat propelan yang dikonsumsi adalah dorongan khusus roket spesifik . Propelan dengan impuls spesifik yang lebih tinggi dikatakan lebih efisien karena lebih banyak dorongan dihasilkan per unit propelan.

The lower rocket stage typically uses high-density propellants (low volume per unit mass) due to its lighter capacity to the propellant weight ratio and because higher performance propellants require higher expansion ratios for maximum performance than can be achieved when operated in the atmosphere. Thus, the first-phase Saturn V uses liquid-kerosene oxygen instead of liquid oxygen-liquid oxygen used at its upper stage. Likewise, Space Shuttle uses high-density, high-density solid rocket boosters for its removal with liquid oxygen-hydrogen liquid. The Space Shuttle Main Engines are used partly for the lift-off but mainly for orbital insertion.

Maps Rocket propellant

History

Solid rocket propellants were first developed during the 13th century under the Song Chinese dynasty, when bows, arrows and launchers of projectile launchers were state-of-the-art military technology in medieval Europe. Song Chinese first used solid propellant (chemical gunpowder) in 1232 during the Kaifeng military siege.

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Chemical propellant

There are four main types of chemical rocket propellants: solid, stored liquids, cryogenic liquids, and liquid monopropellants. The solid/liquid hybrid bi-propellant rocket engine also begins to see limited use.

Solid propellant

Description

Solid propellants are "composites" consisting mostly of large or single, double, or triple macroscopic particles (depending on the number of main ingredients), which is a homogeneous mixture of one or more of the main ingredients. The composites typically comprise a mixture of solid oxidizing granules (eg ammonium nitrate, ammonium dinitramide, ammonium perchlorate, potassium nitrate) in polymer binder (bonding agent) with flake or powder energetic compounds (eg RDX, HMX), metal additives (eg aluminum , beryllium), plasticizer, stabilizer, and/or combustion rate gauge (iron oxide, copper oxide). Single, double, or triple bases are mixtures of fuels, oxidizers, binders and plasticizers that are macroscopically indistinguishable and often mixed as liquids and healed in a single batch. Often, material from double-base propellant has many roles. For example, RDX is a fuel and oxidizer, while nitrocellulose is a fuel, oxidizer, and plasticizer. Further complicated categorization, there are many propellants which contain elements of double and composite base propellants, which often contain some amount of homogenous mixed additive into the binder. In the case of gunpowder (composite pressed without polymer binder) the fuel is charcoal, the oxidant is potassium nitrate, and sulfur serves as a catalyst. (Note: sulfur is not a true catalyst in gunpowder as it is widely used for various reaction products such as K ₂ S.) During the 1950s and 60s researchers in the United States developed composite ammonium perchlorate composite (APCP ). This mixture is typically 69-70% ammonium perchlorate (oxidizer), combined with a fine 16-20% aluminum powder (fuel), incorporated in an 11-14% polybutadiene acrylonitrile (PBAN) or hydroxyl-terminated polybutadiene (rubber fuel polybutadiene). This mixture is formed as a thickened liquid and then put into the correct form and healed into a solid but flexible solid. Historically, compute of APCP solid propellant is relatively small. The military, however, uses various types of solid propellants some of which exceed APCP performance. The highest specific impulse comparison achieved with the various combinations of solid and liquid propellant used in the launch vehicle is currently given in an article on solid fuel rockets.

Advantages

Solid propellant rockets are much easier to store and handle than liquid propellant rockets. The high propellant density makes it a compact size as well. These features plus simplicity and low cost make solid rocket propellers ideal for military applications. In the 1970s and 1980s, the US switched fully to compacted ICBMs: LGM-30 Minuteman and LG-118A Peacekeeper (MX). In the 1980s and 1990s, the Soviet Union/Russia also deployed solid-fuel ICBM (RT-23, RT-2PM, and RT-2UTTH), but retained two fuel-driven ICBMs (R-36 and UR -100N). All solid-fueled ICBM on both sides have three solid initial stages, and those with multiple targeted warheads have a precision maneuverable bus that is used to adjust the trajectory of the re-entry vehicle. ICBM Minuteman III AS was reduced to a single warhead in 2011 in accordance with the START agreement that left only the Trident Naval ICBM with multiple warheads.

Their simplicity also makes solid rockets a good choice whenever a large amount of thrust and cost is a problem. Space Shuttle and many other orbital launch vehicles use solid-fuel rockets in a solid rocket booster stage for this reason.

Losses

With respect to liquid fuel rockets, solid fuel rockets have a lower specific drive, the size of propellant efficiency. The propellant mass ratio of the upper stages of strong propellant is typically in the range of 0.91 to 0.93 which is as good or better than most upper steps of liquid propellant but overall performance is less than for liquid stages due to lower exhaust of solids. speed. The high possible mass ratios with the unsegmented are the result of high propellant densities and very strong wound-to-weight motor-filament motor ratios. A disadvantage for solid rockets is that they can not be blocked in real time, although a programmable thrust schedule can be created by adjusting the interior propellant's geometry. Solid rockets can be released to extinguish combustion or retractable as a means of controlling the range or accommodating the separation of warheads. Casting large amounts of propellant requires consistency and repetition guaranteed by computer control. Casting voids in the propellant can affect the combustion rate so that mixing and casting takes place under vacuum and the mixture of scattered propellants is scattered and scanned to ensure no large gas bubbles are inserted into the motor. Solid fuel rockets are intolerant of cracks and cavities and often require post processing such as X-ray scans to identify errors. Since the combustion process depends on the fuel surface area; voids and cracks represent local increases in burning surface area. It increases local temperature, system pressure and radiant heat flux to the surface. This positive feedback loop further increases the burn rate and can easily lead to catastrophic failure usually due to failure or damage to the nozzle system.

Liquid propellant

Current type

The most common liquid liquids in use today:

• Liquid oxygen (LOX) and very fine kerosene (RP-1). Used for the first stages of Saturn V, Atlas V and Falcon, Russian Soyuz, Zenit Ukraine, and development rockets such as Angara and Long March 6. Very similar to Robert Goddard's first rocket, this combination is widely regarded as the most practical for boosters raised in ground surface and therefore must operate at full atmospheric pressure.
• LOX and liquid hydrogen, used in Space Shuttle orbiter, Atlas V upper stage centaurs, upper stage Saturn V, newer Delta IV rockets, H-IIA rockets, and most of the European Ariane 5 rockets.
• Dinitrogen tetroxide (N ₂ O ₄ ) and hydrazine (N ₂ H ₄ ), MMH, or UDMH. Used in military, orbital, and remote rockets because these two liquids can be stored for long periods at a reasonable temperature and pressure. N ₂ O ₄ /UDMH is the main fuel for Proton rockets, Long March long rockets (LM 1-4), PSLV, and Fregat and Briz-M top levels. This combination is hipergolic, making an interesting simple ignition sequence. The major discomfort is that this propellant is highly toxic, requiring careful handling.
• Monopropellants such as hydrogen peroxide, hydrazine and nitrous oxide are primarily used for attitude control and maintenance of space stations where their long-term storage, simplicity of use, and the ability to provide the required small impulses exceed their lower specific impulses compared with bipropellants. Hydrogen peroxide is also used to drive the turbopump in the first stage of the Soyuz launch vehicle.

History history

These include propellants such as the letters-coded rocket propellants used by Germans in World War II used for Messerschmitt Me 163 Comet Walter HWK 109-509 motor and pioneer SR-2 pioneer SRBM, and Soviet/Russian utilized syntin , the synthetic cyclopropane, C ₁₀ H ₁₆ used on Soyuz U2 until 1995. Syntin develops a specific impulse about 10 seconds larger than kerosene.

Benefits

Liquid-fuel rockets have higher specific impulses than solid rockets and can be strangled, switched off, and restarted. Only the combustion chamber of a liquid-fueled rocket must be resistant to combustion pressure and high temperature and they can be regeneratively cooled by liquid propellant. In vehicles using turbopumps, the propellant tank is at a much lower pressure than the combustion chamber. For this reason, most orbital launch vehicles use liquid propellants.

The main performance advantage of liquid propellant is due to oxidizing agent. Some practical liquid oxidizers (liquid oxygen, nitrogen tetroxide, and hydrogen peroxide) are available which have better specific impulses than ammonium perchlorate used in most solid rockets, when paired with a comparable fuel. These facts have led to the use of hybrid propellants: stored oxidizers used with solid fuels, which retain most of the virtues of both fluids (high ISPs) and solids (simplicity). (New nitramine solid propellants based on CL-20 (HNIW) can match the performance of NTO/UDMH liquid storage propellants, but can not be controlled as well as stored liquids.)

While liquid propellants are cheaper than solid propellant, for orbital launchers, no cost savings, and historically unimportant; the cost of propellant is a very small part of the overall cost of the rocket. Some propellants, especially oxygen and nitrogen, may be collected from the upper atmosphere, and transferred into low Earth orbit for use in depot propellants at a much reduced cost.

Disadvantages

The main difficulty with liquid propellant also with oxidation. It is generally at least quite difficult to store and handle because of its high reactivity with common ingredients, may have extreme toxicity (nitric acid, nitrogen tetroxide), requires moderate cryogenic storage (liquid oxygen), or both (FLOX, fluorine/LOX mixture ). Several exotic oxidations have been proposed: liquid ozone (O <3 ), ClF ₃ , and ClF ₅ , all of which are not stable, energetic, and toxic.

Liquid-fuel rockets also require potentially troublesome valves and seals and a thermally suppressed combustion chamber, which increases rocket costs. Many employ specially designed turbopumps that raise costs greatly because of the difficult fluid flow patterns present in the casing.

Gas propellant

Gas propellant usually involves some sort of compressed gas. However, due to the low density of the gas and the high weight of the pressure vessel required to accommodate it, the gases see little current use but are sometimes used for vernier machines, especially with inert propellants such as nitrogen.

GOX (oxygen gas) is used as an oxidizer for Buran program orbital maneuvering system.

Hybrid propellant

Hybrid rockets typically have solid fuels and liquid or NEMA oxidators. The oxidizing fluid can make it possible to throttle and revive the motor such as a liquid-fueled rocket. Hybrid rockets can also be safer in terms of the environment than solid rockets because some high-performance solid-phase oxidation contains chlorine (especially composites with ammonium perchlorate), compared to the more benign oxygenated liquid or nitrogen oxides often used in hybrids. This only applies to certain hybrid systems. There are hybrids that have used chlorine or fluorine compounds as oxidizing agents and harmful substances such as beryllium compounds that are mixed into solid fuel. Since only one constituent is fluid, hybrids can be simpler than liquid rockets depending on the motive force used to transport fluid into the combustion chamber. Less fluid typically means fewer and smaller piping systems, valves, and pumps (if used).

Hybrid motors suffer from two major drawbacks. The first, along with a solid rocket motor, is that the casing around the fuel grains must be built to withstand full combustion pressures and often extreme temperatures as well. However, modern composite structures handle this problem well, and when used with nitrous oxide and solid rubber propellant (HTPB), a relatively small percentage of fuel is required, so the combustion chamber is not too large.

The main difficulty left with hybrids is by mixing the propellant during the combustion process. In solid propellants, oxidizers and fuels are mixed at the plant under carefully controlled conditions. The liquid propellant is generally mixed by the injector at the top of the combustion chamber, which directs many small streams of fuel and oxidants that move rapidly to one another. The design of a liquid-fueled injector injector has been studied very long and still rejects reliable performance predictions. In hybrid motors, mixing occurs on the surface of a fuel that melts or evaporates. Mixing is not a well-controlled process and generally, quite a lot of propellant is left unburnt, which limits the efficiency of the motor. The rate of fuel combustion is largely determined by the oxidation flux and the open fuel surface area. This burning rate is usually not sufficient for high power operations such as an impulse stage except for surface area or high oxidizing flux. Overly high oxidation flux can cause flooding and loss of locally available fire-extinguishing grip. The surface area can be increased, usually with longer grains or multiple ports, but this can increase the size of the combustion chamber, reducing grain strength and/or reducing volumetric loading. In addition, because burns continue, the hole in the center of the grain ('port') widened and the mixed ratio tended to be more rich oxidizer.

There has been less hybrid motor development than solid and liquid motors. For military use, ease of handling and maintenance has encouraged the use of solid rockets. For orbital work, liquid fuels are more efficient than hybrids and most of the development is concentrated there. Recently there has been an increase in the development of hybrid motors for nonmetallic suborbital work:

• Some universities have recently experimented with hybrid rockets. Brigham Young University, Utah University and Utah State University launched a student-designed rocket called Unity IV in 1995 that burned hydrolyzed polybutadiene solid fuel (HTPB) with an oxygen gas oxidizer, and in 2003 launched a larger version that burned HTPB with nitrous oxide. Stanford University studied hybrid oxide nitric oxide/paraffinic motors. UCLA has launched a hybrid rocket through a group of undergraduate students since 2009 using HTPB.
• The Rochester Institute of Technology builds HTPB hybrid rockets to launch small payloads into space and to some near-Earth objects. The first launch was in Summer 2007.
• SpaceShipOne scale composite, the first private manned spacecraft, powered by a hybrid rocket that burns HTPB with nitrous oxide: RocketMotorOne. Hybrid rocket engines are manufactured by SpaceDev. SpaceDev partially bases its motor on experimental data collected from AMROC (American Rocket Company) motor testing at NASA Stennis Space Center's E1 stand.
• Dream Chaser spacecraft intends to use twin hybrid engines with similar designs for SpaceShipOne for enhanced orbit, deorbiting, and emergency escape systems.

Gel propellant

Some work has been done on gelling of liquid propellant to provide propellant with low vapor pressure to reduce the risk of unintentional fireballs. Gel propellants behave like solid propellants in storage and such as liquid propellants are used.

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Inert propellant

Some rocket designs have propellants getting their energy from non-chemical or even external sources. For example, water rockets use compressed gas, usually air, to force water out of a rocket.

Solar thermal rockets and nuclear thermal rockets typically propose to use liquid hydrogen to specify about 600-900 seconds, or in some cases, depleted water. as a vapor for I _sp about 190 seconds.

In addition to low performance requirements such as attitude control jets, inert gases such as nitrogen have been used.

The nuclear thermal rocket passes propellant over the central reactor, heats the propellant and causes it to expand rapidly out of the rocket nozzle, pushing the plane forward. The propellant itself does not directly interact with the interior of the reactor, so the propellant is not irradiated.

The solar thermal rockets use concentrated sunlight to heat the propellant, rather than using a nuclear reactor.

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Mixed ratio

The theoretical discard velocity of determined propellant chemistry is a function of the energy released per unit of mass of propellant (specific energy). Unburned fuel or oxidizer attracts specific energy. However, most rockets run a rich mix of fuel.

Penjelasan umum untuk campuran kaya bahan bakar adalah bahwa campuran kaya bahan bakar memiliki knalpot berat molekul yang lebih rendah, yang dengan mengurangi ${\ displaystyle M}  ÂÂ$ meningkatkan rasio ${\ displaystyle {\ frac {\ sqrt {T_ {c}}} {M}}}  ÂÂ$ yang kira-kira sama dengan kecepatan buang teoretis. Campuran kaya bahan bakar sebenarnya memiliki kecepatan knalpot teoritis yang lebih rendah, karena ${\ displaystyle {\ sqrt {T_ {c}}}}  ÂÂ$ menurun secepat atau lebih cepat dari ${\ displaystyle M}  ÂÂ$ .

The rocket nozzle converts heat energy from propellant into directed kinetic energy. This conversion happens in a short time, in the order of one millisecond. During the conversion, energy must be transferred very quickly from the rotation and vibration state of the exhaust molecule to translation. Molecules with fewer atoms (such as CO and H ₂ ) store less energy in vibration and rotation than molecules with more atoms (such as CO ₂ and H ₂ O). These smaller molecules transfer more of their rotational and vibrational energy to translational energy than larger molecules, and the resulting increase in the nozzle efficiency is large enough that the real rocket engine increases actual exhaust speed by running a rich mixture with theoretical exhaust velocity lower.

The effect of the molecular weight of the exhaust on the nozzle efficiency is the most important for nozzles operating near the surface of the ocean. High expansion rockets that operate in a vacuum see a much smaller effect, and therefore run less rich. The Saturn-II stage (LOX/LH ₂ rocket) varies the mixed ratio during flight to optimize performance.

LOX/hydrocarbon rockets only run somewhat rich (O/F 3 mass ratio rather than stoichiometry 3.4 to 4) because the release of energy per unit mass falls rapidly because of the mixed ratio deviates from stoichiometry. LOX/LH ₂ rockets run very rich (O/F 4 mass ratio rather than stoichiometric 8) because hydrogen is so light that the energy release per unit of propellant mass falls very slowly with extra hydrogen. In fact, the LOX/LH ₂ rockets are generally limited to how rich they are run by mass performance penalties from the extra hydrogen tank, rather than the hydrogen mass itself.

Another reason to run rich is that the off-stoichiometric mixture burns colder than the stoichiometric mix, which makes engine cooling easier. Since fuel-rich combustion products are less chemically (corrosive) than oxygen products, most rocket engines are designed to run rich fuels, with at least one exception for Russia's RD-180 preburner, which burns LOX and RP-1 with a ratio of 2 , 72.

In addition, the mixed ratio can be dynamic during launch. This can be utilized with a design that adjusts the oxidator ratio to the fuel (along with overall drive) during the flight to maximize overall system performance. For example, as long as the thrust power of the thrust is premium while the specific impulse is less so. Thus, the system can be optimized by adjusting the O/F ratio carefully so that the engine runs cooler at higher thrust levels. It also allows the engine to be designed a bit more compactly, increasing its overall thrust on weight performance.

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Propellant density

Although liquid hydrogen gives high I _sp , its low density is a significant loss: hydrogen occupies about 7x more volume per kilogram than solid fuel such as kerosene. It not only punishes tankers, but also pipes and fuel pumps that lead from the tank, which needs to be 7x bigger and heavier. (The oxidizing side of the engine and the tank is of course not affected.) This makes the vehicle dry mass much higher, so the use of liquid hydrogen is not as favorable as expected. Indeed, some solid hydrocarbon/LOX propellant combinations have higher performance when dry mass penalties are included.

Due to lower I _sp , the solid propellant launch vehicle has a higher takeoff mass, but this does not mean a high proportionate cost; otherwise, the vehicle may end up cheaper. Liquid hydrogen is a fuel that is quite expensive to produce and store, and causes many practical difficulties with the design and manufacture of vehicles.

Due to a higher overall weight, a fuel-intensive launch vehicle necessarily requires a higher takeoff thrust, but brings this thrusting ability to orbit. This, in combination with a better thrust/weight ratio, means that solid fuel vehicles reach orbit earlier, thus minimizing losses due to gravity. Thus, the effective delta-v requirements for this vehicle are reduced.

However, liquid hydrogen does not provide a clear advantage when the overall mass needs to be minimized; for example, Saturn V vehicles use it at the top level; This weight loss means that the first phase of solid fuel can be made smaller, saving considerable money.

Tripropelant rocket designs often try to use the optimal propellant blend for launch vehicles. It mainly uses solid fuel while at low altitudes and switches to hydrogen at higher altitudes. The study by Robert Salkeld in the 1960s proposed SSTO using this technique. Space Shuttle estimates this by using a solid solid rocket booster for the majority of thrust during the first 120 seconds, the main engine, burning a fuel-rich mixture of hydrogen and oxygen to operate continuously during launch but only provides the majority of thrust on the higher. altitude after the BPRS blackout.

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See also

• ALICE (propellant)
• Trinitramide
• Timeline of hydrogen technology
• Category: Rocket fuel
• Comparison: Aviation fuel
• The nuclear drive
• Ion thruster
• Crawford burner

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References

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External links

• Rocket Propellers (from Rocket & Space Technology )
• List of rocket, practical and theoretical rock detail
• Short Rocket Essay by S. Abbas Raza on solid rocket fuel development at 3 Quarks Daily

Source of the article : Wikipedia