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Resistojet Rocket
A resistojet is a method of spacecraft propulsion (electric propulsion) that provides thrust by heating a typically non-reactive fluid. Heating is usually achieved by sending electricity through a resistor consisting of a hot incandescent filament, with the expanded gas expelled through a conventional nozzle. Resistojets have been flown in space since 1965 on board military Vela satellites. However, they only became used in commercial applications in 1980 with the launch of the first satellites in the Intelsat-V program. Many GEO spacecraft, and all 95 Iridium, used Aerojet MR-501/ MR-502 series resistojet engines. Nowadays resistojet propulsion is used for orbit insertion, attitude control, and deorbit of LEO satellites, and do well in situations where energy is much less of a constraint than mass, and where propulsion efficiency needs to be reasonably high but low thrust is acceptable. Resistojets have also been proposed as means of using biowaste as reaction mass, particul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spacecraft Propulsion
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric entry. Several methods of pragmatic spacecraft propulsion have been developed, each having its own drawbacks and advantages. Most satellites have simple reliable chemical thrusters (often monopropellant rockets) or resistojet rockets for orbital station-keeping, while a few use Reaction wheel, momentum wheels for attitude control. Russian and antecedent Soviet bloc satellites have used Spacecraft electric propulsion, electric propulsion for decades, and newer Western geo-orbiting spacecraft are starting to use them for north–south station-keeping and orbit raising. Interplanetary vehicles mostly use chemical rockets as well, although a few have used electric propulsion such as ion thrusters and Hall-effect thrusters. Various technologies ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thrust
Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that system. The force applied on a surface in a direction perpendicular or normal to the surface is also called thrust. Force, and thus thrust, is measured using the International System of Units (SI) in newtons (symbol: N), and represents the amount needed to accelerate 1 kilogram of mass at the rate of 1 meter per second per second. In mechanical engineering, force orthogonal to the main load (such as in parallel helical gears) is referred to as static thrust. Examples A fixed-wing aircraft propulsion system generates forward thrust when air is pushed in the direction opposite to flight. This can be done by different means such as the spinning blades of a propeller, the propelling jet of a jet engine, or by ejecting hot gases f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Electric Propulsion
Solar electric propulsion (SEP) is the combination of solar cells and electric thrusters to propel a spacecraft through outer space. This technology has been exploited in a variety of spacecraft designs by the European Space Agency (ESA), the JAXA (Japanese Space Agency), Indian Space Research Organisation (ISRO) and NASA. SEP has a significantly higher specific impulse than chemical rocket propulsion, thus requiring less propellant mass to be launched with a spacecraft. The technology has been evaluated for missions to Mars. Overview Solar electric propulsion combines solar panels on spacecraft and one or more electric thrusters, used in tandem. There are many different types of electric thrusters, including a so-called ion thruster, a term that is often incorrectly used to describe all types of electric thrusters. It is also possible to generate electricity from the Sun without using photovoltaic panels, such as with solar concentrators and a Stirling engine. A 50 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Liquid-propellant Rocket
A liquid-propellant rocket or liquid rocket uses a rocket engine burning liquid rocket propellant, liquid propellants. (Alternate approaches use gaseous or Solid-propellant rocket , solid propellants.) Liquids are desirable propellants because they have reasonably high density and their combustion products have high Specific impulse, specific impulse (''I''sp). This allows the volume of the propellant tanks to be relatively low. Types Liquid rockets can be monopropellant rockets using a single type of propellant, or bipropellant rockets using two types of propellant. Tripropellant rockets using three types of propellant are rare. Liquid oxidizer propellants are also used in hybrid rockets, with some of the advantages of a solid rocket. Bipropellant liquid rockets use a liquid fuel such as liquid hydrogen or RP-1, and a liquid oxidizer such as liquid oxygen. The engine may be a cryogenic rocket engine, where the fuel and oxidizer, such as hydrogen and oxygen, are gases which hav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solid-propellant Rocket
A solid-propellant rocket or solid rocket is a rocket with a rocket engine that uses solid propellants (fuel/ oxidizer). The earliest rockets were solid-fuel rockets powered by gunpowder. The inception of gunpowder rockets in warfare can be credited to the ancient Chinese, and in the 13th century, the Mongols played a pivotal role in facilitating their westward adoption. All rockets used some form of solid or powdered propellant until the 20th century, when liquid-propellant rockets offered more efficient and controllable alternatives. Because of their simplicity and reliability, solid rockets are still used today in military armaments worldwide, model rockets, solid rocket boosters and on larger applications. Since solid-fuel rockets can remain in storage for an extended period without much propellant degradation, and since they almost always launch reliably, they have been frequently used in military applications such as missiles. The lower performance of solid propellant ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arcjet Rocket
An arcjet rocket or arcjet thruster is a form of electrically powered spacecraft propulsion, in which an electrical discharge ( arc) is created in a flow of propellant (typically hydrazine or ammonia). This imparts additional energy to the propellant, so that one can extract more work out of each kilogram of propellant, at the expense of increased power consumption and (usually) higher cost. Also, the thrust levels available from typically used arcjet engines are very low compared with chemical engines. When the energy is available, arcjets are well suited to keeping stations in orbit and can replace monopropellant rockets. Aerojet MR-510 series arcjet engines are currently used on Lockheed Martin A2100 satellites using hydrazine as a propellant, providing over 585 s average specific impulse at 2 kW. In Germany, researchers at the University of Stuttgart's Institute of Space Aviation Systems have been working with arcjets for years and have developed various hydrogen-powered arc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Small Satellite
A small satellite, miniaturized satellite, or smallsat is a satellite of low mass and size, usually under . While all such satellites can be referred to as "small", different classifications are used to categorize them based on mass. Satellites can be built small to reduce the large economic cost of launch vehicles and the costs associated with construction. Miniature satellites, especially in large numbers, may be more useful than fewer, larger ones for some purposes – for example, gathering of scientific data and radio relay. Technical challenges in the construction of small satellites may include the lack of sufficient power storage or of room for a propulsion system. Rationales One rationale for miniaturizing satellites is to reduce the cost; heavier satellites require larger rockets with greater thrust that also have greater cost to finance. In contrast, smaller and lighter satellites require smaller and cheaper launch vehicles and can sometimes be launched in mult ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Specific Impulse
Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine, such as a rocket engine, rocket using propellant or a jet engine using fuel, generates thrust. In general, this is a ratio of the ''Impulse (physics), impulse'', i.e. change in momentum, ''per mass'' of propellant. This is equivalent to "thrust per massflow". The resulting unit is equivalent to velocity. If the engine expels mass at a constant exhaust velocity v_e then the thrust will be \mathbf = v_e \frac . If we integrate over time to get the total change in momentum, and then divide by the mass, we see that the specific impulse is equal to the exhaust velocity v_e . In practice, the specific impulse is usually lower than the actual physical exhaust velocity inefficiencies in the rocket, and thus corresponds to an "effective" exhaust velocity. That is, the specific impulse I_ in units of velocity *is defined by* : \mathbf = I_ \frac , where \mathbf is the average thrust. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cold Gas Thruster
A cold gas thruster (or a cold gas propulsion system) is a type of rocket engine which uses the expansion of a (typically inert) pressurized gas to generate thrust. As opposed to traditional rocket engines, a cold gas thruster does not house any combustion and therefore has lower thrust and specific impulse, efficiency compared to conventional monopropellant and Liquid-propellant rocket, bipropellant rocket engines. Cold gas thrusters have been referred to as the "simplest manifestation of a rocket engine" because their design consists only of a fuel tank, a regulating valve, a propelling nozzle, and the little required plumbing. They are the cheapest, simplest, and most reliable propulsion systems available for orbital maintenance, maneuvering and Spacecraft attitude control, attitude control. Cold gas thrusters are predominantly used to provide stabilization for smaller space missions which require contaminant-free operation. Specifically, CubeSat propulsion system development ha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monopropellant Rocket
A monopropellant rocket (or "monochemical rocket") is a rocket that uses a single chemical as its propellant. Monopropellant rockets are commonly used as small attitude and trajectory control rockets in satellites, rocket upper stages, crewed spacecraft, and spaceplanes. Chemical-reaction based monopropellant rockets The simplest monopropellant rockets depend on the chemical decomposition of a storable propellant after passing it over a catalyst bed. The power for the thruster comes from the high pressure gas created during the decomposition reaction that allows a Rocket engine nozzle, rocket nozzle to speed up the gas to create thrust. The most commonly used monopropellant is hydrazine (), a compound unstable in the presence of a Catalysis, catalyst and which is also a strong reducing agent. The most common catalyst is granular alumina (aluminum oxide, ) coated with iridium. These coated granules are usually under the commercial labels Aerojet S-405 (previously made by Shell plc, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heating Element
A heating element is a device used for conversion of electric energy into heat, consisting of a heating resistor and accessories. Heat is generated by the passage of electric current through a resistor through a process known as Joule heating. Heating elements are used in household appliances, industrial equipment, and scientific instruments enabling them to perform tasks such as cooking, warming, or maintaining specific temperatures higher than the ambient. Heating elements may be used to transfer heat via Thermal conduction, conduction, convection, or radiation. They are different from devices that generate heat from electrical energy via the Peltier effect, and have no dependence on the direction of electrical current. Principles of operation Resistance & resistivity Materials used in heating elements have a relatively high Electrical resistivity and conductivity, electrical resistivity, which is a measure of the material's ability to resist electric current. The Electri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cubic Zirconia
Cubic zirconia (CZ) is the cubic crystalline form of zirconium dioxide (ZrO2). The synthesized material is hard and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirconium silicate (ZrSiO4). It is sometimes erroneously called ''cubic zirconium''. Because of its low cost, durability, and close visual likeness to diamond, synthetic cubic zirconia has remained the most gemologically and economically important competitor for diamonds since commercial production began in 1976. Its main competitor as a synthetic gemstone is a more recently cultivated material, synthetic moissanite. Technical aspects Cubic zirconia is crystallographically isometric, an important attribute of a would-be diamond simulant. During synthesis zirconium oxide naturally forms monoclinic crystals, which are stable under normal atmospheric conditions. A stabilizer is required for cubic crystals (taking on the fluorite structure) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
