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# Topic: Specific impulse

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 Specific impulse - Wikipedia, the free encyclopedia The specific impulse is a measure of the thrust per unit of propellant that is expelled, while thrust is a measure of the momentary or peak force supplied by a particular engine. The highest specific impulse for a chemical propellant ever test-fired in a rocket engine was lithium, fluorine, and hydrogen (a tripropellant): 542 seconds (5320 m/s). For a delta-v that is larger than the specific impulse, this requirement of carrying the fuel and spending much of the fuel on accelerating the fuel, gives rise to an exponential increase in fuel requirement (and larger tanks which also add to the mass). en.wikipedia.org /wiki/Specific_impulse   (2137 words)

 Kids.Net.Au - Encyclopedia > Specific impulse   (Site not responding. Last check: 2007-10-16) The specific impulse of a rocket propellant is a rough measure of how fast the propellant is ejected out of the back of the rocket. Alternatively the specific impulse is defined as the change in momentum per unit weight: The specific impulse for various means of propulsion are given in the entry for spacecraft propulsion. www.kids.net.au /encyclopedia-wiki/sp/Specific_impulse   (224 words)

 Specific impulse   (Site not responding. Last check: 2007-10-16) In other words, the specific impulse is a measure of how much push can be obtained from a fixed mass of fuel. The specific impulse of a rocket propellant is a measure of how fast the propellant is ejected out of the back of the rocket. The specific impulses for various means of propulsion are given in the entry for spacecraft propulsion. www.serebella.com /encyclopedia/article-Specific_impulse.html   (673 words)

 Kids.Net.Au - Encyclopedia > Variable specific impulse magnetoplasma rocket   (Site not responding. Last check: 2007-10-16) Variable specific impulse magnetoplasma rockets or VASIMRs as the name is commonly abbreviated is a hypothetical form of spacecraft propulsion that uses radio waves and magnetic fields to accelerate a propellant[?]. VASIMRs bridge the gap between high-thrust low-specific impulse propulsion systems and low-thrust high-specific impulse systems, being capable of functioning in either mode simply by adjusting its parameters of operation. Closing the choke shifts the rocket into high gear; it reduces the number of ions exiting the drive (thus producing less thrust), but keeps their temperature high (thus increasing specific impulse). www.kids.net.au /encyclopedia-wiki/va/Variable_specific_impulse_magnetoplasma_rocket   (368 words)

 Variable specific impulse magnetoplasma rocket - Wikipedia, the free encyclopedia The Variable specific impulse magnetoplasma rocket (VASIMR) is a hypothetical form of spacecraft propulsion that uses radio waves and magnetic fields to accelerate a propellant. VASIMRs are intended to bridge the gap between high-thrust, low-specific impulse propulsion systems and low-thrust, high-specific impulse systems, as they are capable of functioning in either mode simply by adjusting their parameters of operation. Current VASIMR designs should be capable of producing specific impulses ranging from 10,000-300,000 m/s (1,000-30,000 seconds) - the low end of this range is comparable to some ion thruster designs. en.wikipedia.org /wiki/Variable_specific_impulse_magnetoplasma_rocket   (488 words)

 Nuclear-Heated Steam Rocket Using Lunar Ice The specific impulse is proportional to the square root of the propellant mixed mean outlet temperature. The focus of this analysis is to determine the thrust-per-weight (specific power) and specific impulse (temperature) values that a nuclear-heated steam rocket must achieve if it is both to launch from the lunar surface and to use the lunar water most efficiently. The specific impulse implies a mixed mean outlet temperature of 1100 K. Calculations show the Baseline NSR infrastructure masses to be a factor between 150 and 720 lower than those of the cryo system. neofuel.com /moonicerocket   (4929 words)

 Let's be Specific Specific is a scientific term meaning "divided by weight or mass", You have probably encountered other "specific" terms in physics and chemistry. The specific volume of a gas is the volume of the gas divided by the mass of the gas contained in the volume. Specific gravity is the weight of an object divided by the weight of the same volume of water. www.grc.nasa.gov /WWW/K-12/airplane/spec.html   (286 words)

 Specific impulse In other words, the specific impulse is a measure of how much push can be obtained from a fixed mass of fuel. In free fall, the exhaust velocity determines how much the engine can change the velocity of the spacecraft without heroic measures — for changes in velocity that are large compared to the exhaust velocity, the amount of fuel required is exponential in the change in velocity needed. The specific impulses for various means of propulsion are given in the entry for spacecraft propulsion. www.abacci.com /wikipedia/topic.aspx?cur_title=Specific_impulse   (506 words)

 Electrothermally augmented hydrazine thruster - Patent 4305247 Specific impulse of hydrazine thruster is augmented by electrothermally heating the hot gas in heater passages 36 and 37 as it passes from hydrazine dissociation chamber 14 to thrust nozzle 28. This invention is directed to a hydrazine thruster which has augumented specific impulse by heating of the gases which are the product of hydrazine dissociation. The electrothermal augumentation of the specific impulse provides a system in which thrust is achieved even with electrical failure, but without the augumentation provided. www.freepatentsonline.com /4305247.html   (1386 words)

 Space Propulsion Let's do it Better Electrically   (Site not responding. Last check: 2007-10-16) The practical implication of specific impulse can immediately be seen by considering the amount of propellant needed to provide a certain total impulse. Thus, if a system were operating at a specific impulse of 300 seconds, 200 pounds of propellant would be required to provide a total impulse of 60,000 pound-seconds. If the launch vehicle propellant were given a specific impulse of approximately 2400 seconds, then the system at launch would weigh only about 1.4 times as much as the weight placed into orbit. www.airpower.maxwell.af.mil /airchronicles/aureview/1973/Nov-Dec/baty.html   (5321 words)

 Rocket Tutorial from ATI Space and Defense Technical Training Courses However, in practice the specific impulse is usually regarded as a measure of the efficiency of the propellant alone. By the rocket equation, assuming a specific impulse of 300 seconds, the fraction of the separated mass consumed by the propellant for the apogee maneuver is 46 percent from Cape Canaveral, 40 percent from Kourou, and 39 percent from the equator. The specific impulse is 4300 seconds, the mass flow rate is 4 mg/s, and the thrust is 165 mN. www.catalog.com /hitekweb/rocket_tutorial.htm   (3806 words)

 Specific Impulse Inc. Press Release Specific Impulse's scalable solutions are designed for ease of use by marketing professionals, and require no knowledge of HTML or other web technologies. Specific Impulse is privately held, with offices in San Jose and Oakland, California. Specific Impulse™, StageOne™, IntraStar™, and MissionControl™ are trademarks of Specific Impulse Inc. Other trademarks are the property of their respective owners. www.specific-impulse.com /content/view_press_release_373.html   (370 words)

 Space Propulsion Let's do it Better Electrically   (Site not responding. Last check: 2007-10-16) Total impulse establishes the magnitude of the thrust and the duration of the thrusting time that are necessary to complete a certain mission. Specific impulse is generally defined as the velocity imparted to the propellant divided by gravitational acceleration. As mentioned at the first of this section, the use of high specific impulse devices to perform the launching function could reduce the size of the launching vehicle to roughly the size of the payload. airpower.maxwell.af.mil /airchronicles/aureview/1973/Nov-Dec/baty.html   (5329 words)

 Specific impulse - Education - Information - Educational Resources - Encyclopedia - Music The specific impulse of a rocket (commonly abbreviated I In this sense, specific impulse is defined as the change in momentum per unit weight: The specific impulse in seconds is the time one kilogram of fuel lasts if a one-earth-gravity thrust (including for example a hypothetical hovering over the Earth) is applied to a mass of one kilogram. www.music.us /education/S/Specific-impulse.htm   (1099 words)

 TECH ISP - Solar Electric Propulsion Potential Mission Applications   (Site not responding. Last check: 2007-10-16) The fundamental performance expectation of a space mission, regardless of propulsion type, is specified by the "Rocket Equation", which relates the ratio of final to initial masses to the ratio of the Delta V to the specific impulse, which is proportional to the propellant velocity. The trends shown on Figure 2 then imply that for a given mission there is a specific impulse that minimizes the total mass of the electric propulsion system (which is closely approximated by the sum of the power and propellant masses). It is important to note that the optimum specific impulse tends to increase both with increasing mission Delta V (as suggested by Figure 1) and with decreasing specific mass (the ratio of total mass to power level) of the spacecraft. www.inspacepropulsion.com /tech/solar_elec_prop__missionapps.html   (1070 words)

 [No title]   (Site not responding. Last check: 2007-10-16) The hypothetical Variable specific impulse magnetoplasma rocket(VASIMR) propulsion should yield a minimum of 10,000-300,000 m/s but will probably require a great deal of heavy machinery to confine even relatively diffuse plasmas, so they will be unusable for very-high-thrust applications such as launch from planetary surfaces. In this sense, specific impulse is defined as the change in momentum per unit weight-on-Earth of the propellent: In rocketry the specific impulse as the impulse per unit mass of propellant used is simply the effective exhaust velocity: www.worldhistory.com /wiki/s/specific-impulse.htm   (2026 words)

 Nuclear-Heated Steam Rocket Using Lunar Ice A first-order derivation and estimates of the power-per-mass and specific impulse yield requirements for a nuclear-heated steam rocket (NSR) to deliver payloads to lunar escape from the lunar south pole. This analysis connects specific power and specific impulse requirements to the required (minimum) nuclear reactor power per volume of nuclear fuel element and the required maximum temperature of the nuclear fuel elements. Specific impulse is a measure of propellant utilization efficiency. www.neofuel.com /moonicerocket   (4929 words)

 Specific impulse   (Site not responding. Last check: 2007-10-16) In other words, the specific impulse is a measure of how much push can be obtained from a fixedmass of fuel. The specific impulse of a rocket propellant is a measure of how fast the propellant isejected out of the back of the rocket. In free fall, the exhaust velocity determines how much the engine can changethe velocity of the spacecraft without heroic measures — for changes in velocity that are large compared to the exhaustvelocity, the amount of fuel required is exponential in the change in velocity needed. www.therfcc.org /specific-impulse-117027.html   (411 words)

 Max Payload per Launch Dollar The rocket scientist uses "specific impulse" as the measure of velocity. The incorrect answer “highest specific impulse” is the equivalent to putting all the available energy into as small a propellant mass as is practical. Higher specific impulses (600 - 900 seconds) such as are achievable using liquid Hydrogen propellant typically result in at least an order of magnitude poorer performance. www.neofuel.com /optimum   (3498 words)

 Nerva Alpha The engine had a mass of 2550 kg and was designed to operate at a specific impulse of 875 s for one hour at a thrust of 73 kN or at a specific impulse of 860 s for two hours at a thrust of 71.7 kN (the Alpha engine). Indications were that the specific impulse degradation during startup and shutdown might be decreased by a factor of two over early rough estimates that were based on linear thrust and linear temperature ramps. The usefulness of the cooldown impulse to the mission depended greatly on where the thrust occurred and this was dependent on the specific mission being analyzed. www.astronautix.com /engines/neralpha.htm   (2914 words)

 Specific impulse - NewMars Specific impulse is a measure of the effectiveness of a fuel in a type of engine, usually for either rockets or jet engines. For a fuel, the specific impulse can be calculated by calculating how many seconds a quantity of fuel could generate enough thrust to support the weight of that mass of fuel. The specific impulse of that fuel would then be 450. www.newmars.com /wiki/index.php?title=Specific_impulse&printable=yes   (225 words)

 Chemical Rocket Launcher Specific impulse describes propulsive efficiency of all contraptions which generate thrust by consuming fuel or rocket propellant. Solid propellant rocket is inexpensive, but has a low specific impulse (2-3 km/s), has to carry heavy casing, and cannot be throttled or stopped; it burns until all the grain is exhausted. Steam rockets cannot be used as rocket launchers because their specific impulse is too low and their dry weight is too high. www.islandone.org /LEOBiblio/SPBI101.HTM   (4559 words)

 Space and its Exploration: How a Solid Propellant Rocket Works   (Site not responding. Last check: 2007-10-16) Specific Impulse, the thrust per unit propellant burned each second, measures rocket performance and more specifically, internal thrust production a product of pressure and heat. In designing the rocket's propellant grain specific impulse must be taken into account since it can be the difference betwixt a conflagration of failure (explosion), and a successfully optimized thrust producing rocket. If a propellant with a high specific impulse is used as the fuel for a rocket whose grain design offers a high surface area ratio, high amounts of thrust will ensue ignition. adc.gsfc.nasa.gov /adc/education/space_ex/solid.html   (894 words)

 Magnetohydrodynamic Ion Drive The specific impulse is defined to be the ratio of the thrust T to the rate of use of the sea level weight of propellant: Specific impulse is essentially an indication of how much a rocket's velocity can be increased by a given amount of fuel[ ]. Specific impulse can be thought of as the gas mileage of the engine. www.madmadscientist.com /iondrive.html   (3254 words)

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