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	<title>SpaceBuild &#187; Chemical</title>
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	<description>Spacecraft technology</description>
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		<title>Liquid Propellant Engines</title>
		<link>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/303/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/303/#comments</comments>
		<pubDate>Sat, 07 Aug 2010 20:41:35 +0000</pubDate>
		<dc:creator>admin</dc:creator>
				<category><![CDATA[Chemical]]></category>

		<guid isPermaLink="false">http://www.spacebuild.net/s1/?p=303</guid>
		<description><![CDATA[Rocket researchers investigating space flight in the 1920s and 1930s knew that old-fashioned fireworks rockets weren&#8217;t really the way of the future for their work, and turned instead to liquid propellants to build the large rocket vehicles they wanted. By the mid-1960s, they had developed liquid-propellant rocket engines powerful enough to put men on the Moon. In its simplest form, a modern liquid propellant rocket engine system consists basically of of a tank of oxidizer and a tank of fuel that feed a combustion chamber, with the combustion exhaust forced out a bell-shaped nozzle. Three classes of liquid propellants are in common use: Liquid oxygen (&#8220;LOX&#8221;) and hydrocarbon fuels, such as gasoline, alcohol, and ultimately kerosene. LOX and liquid hydrogen (&#8220;LOX-LH2&#8242;). &#8220;Storable&#8221; propellants that can be stored at room temperature, as opposed to LOX and LH2, which have to be chilled. Incidentally, most storable propellants have the interesting property of being &#8220;hypergolic&#8221;, meaning they ignite spontaneously when mixed. This makes ignition of a liquid fuel rocket engine using storable propellants very straightforward, but also means that they pose some safety hazards. Of course, a rocket is a very sophisticated piece of hardware, and the simple description above glosses over many [...]]]></description>
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		<title>Shuttle propulsion &#8211; Storables</title>
		<link>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/305/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/305/#comments</comments>
		<pubDate>Wed, 21 Jul 2010 20:46:09 +0000</pubDate>
		<dc:creator>admin</dc:creator>
				<category><![CDATA[Chemical]]></category>
		<category><![CDATA[Vehicle design]]></category>

		<guid isPermaLink="false">http://www.spacebuild.net/s1/?p=305</guid>
		<description><![CDATA[The US space shuttle&#8217;s orbital propulsion system uses storables, and when the orbiter lands a crew in protective clothing has to go out and &#8220;safe&#8221; it before anyone else is allowed to get near. The nasty behaviour of storables means higher cost, and they are also now generally regarded as environmentally unacceptable and avoided when possible. Storables were initially used in military missiles that had to be ready to fire on a moment&#8217;s notice. Their tanks were permanently fueled, capped by seals that were blown at the moment of firing. Solid propellants are now preferred for military missiles, though the Soviets stayed with storables for much longer than the US since they were comfortable with the technology. The Soviets even used them for submarine-launched missiles, despite the threat posed by such toxic and violent chemicals in a closed environment. Storables are still used on spacecraft, such as deep-space probes that will fly through space for years and make occasional engine burns. Obviously there is no practical way to store cryogenic propellants for such a long period of time. Of course, the thruster systems on such spacecraft are also based on storable fuels. Thruster systems are in general simple, very low [...]]]></description>
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		<title>High Energy Density Matter (HEDM)</title>
		<link>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/293/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/293/#comments</comments>
		<pubDate>Tue, 20 Jul 2010 20:21:09 +0000</pubDate>
		<dc:creator>admin</dc:creator>
				<category><![CDATA[Chemical]]></category>

		<guid isPermaLink="false">http://www.spacebuild.net/s1/?p=293</guid>
		<description><![CDATA[In addition to the normal tripropellant approach, researchers have been looking at chemical additives that will increase the specific impulse generated by conventional bipropellant systems. These increases are achieved by adding high-energy chemicals in order to increase Isp, thrust, and safety. This is not unlike adding chemicals to your car&#8217;s fuel tank in order to achieve greater mileage. At the current time, HEDN is still in the basic research phase. In addition to the increase to specific impulse, HEDM additives have the potential to increase propellant and vehicle density, allowing for more compact vehicles. These improvements would allow a higher percentage of deliverable payload weight to vehicle weight in future launch vehicles.]]></description>
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		<title>Tripropellants</title>
		<link>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/291/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/291/#comments</comments>
		<pubDate>Mon, 05 Jul 2010 20:18:00 +0000</pubDate>
		<dc:creator>admin</dc:creator>
				<category><![CDATA[Chemical]]></category>

		<guid isPermaLink="false">http://www.spacebuild.net/s1/?p=291</guid>
		<description><![CDATA[There are many chemical reactions that result in a higher specific impulse than the 423 seconds that is provided by the LH2/LOX workhorse. However, many of these are unacceptable as rocket propellants because the exhaust is not a gas. Tripropellant technologies are an attempt to use these reactions by adding a third component (usually hydrogen) to the fuel and oxidizer. So far, lithium-fluorine-hydrogen and beryllium-oxygen-hydrogen mixes show the most promise for a tripropellant application. (Frisbee, 2000l) The beryllium-oxygen-hydrogen system could generate an Isp of 705 s and is being investigated by the U.S. Air Force. A lithium-fluorine-hydrogen system has the potential for generating an Isp of 705 s. Early testing shows that while it has a higher combustion efficiency than the beryllium-oxygen-hydrogen system, is only allows a slight advantage over a fluorine-hydrogen bipropellant system.]]></description>
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		<title>Bipropellants</title>
		<link>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/289/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/289/#comments</comments>
		<pubDate>Thu, 17 Jun 2010 20:15:20 +0000</pubDate>
		<dc:creator>admin</dc:creator>
				<category><![CDATA[Chemical]]></category>

		<guid isPermaLink="false">http://www.spacebuild.net/s1/?p=289</guid>
		<description><![CDATA[The bipropellant that is most often used in interplanetary spacecraft with relatively small engines is nitrogen tetroxide / monomethyl-hydrazine, commonly referred to as NTO/MMH. This combination yields an Isp of 317 lbf-s/lbm. NASA seeks to improve performance to 326 lbf-s/lbm by using of a rhenium-alloyed thrust chamber, which will allow both higher operating temperatures and pressures. (Frisbee, 2000a) The following table summarizes other bipropellant systems that have been investigated. The &#8220;type&#8221; column describes the how the propellant may be stored. &#8220;Space storable&#8221; refers to combinations that may be stored for extended periods in the space environment. Propellant Type Isp (s) F2/N2H4 Space Storable 376 OF2/B2H6 Space Storable 325 OF2/C2H6 Space Storable 370 OF2/C2H4 Space Storable 375 N2F4/N2H4 Space Storable 358 O2/H2 Refrigerated 423 CIF5/N2H4 Space Storable 329 O2/CH4 Space Storable 330 NTO/MMH Earth Storable 317]]></description>
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		<title>Unusual Liquid propellants</title>
		<link>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/311/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/311/#comments</comments>
		<pubDate>Wed, 19 May 2010 20:53:15 +0000</pubDate>
		<dc:creator>admin</dc:creator>
				<category><![CDATA[Chemical]]></category>

		<guid isPermaLink="false">http://www.spacebuild.net/s1/?p=311</guid>
		<description><![CDATA[A wide range of different liquid propellant combinations have been used for liquid rocket engines, and many combinations are possible. Unusual fuels include ammonia and ethanol (grain alcohol), and there have been some odd combinations of more conventional propellants, such as LOX-UDMH or HTP-RP. Liquid diatomic fluorine (LF2) has been considered as an oxidizer in place of LOX, and LF2-LH2 propulsion actually has specific a few percentage points higher than that of LOX-LH2. It has never been used operationally, apparently because it is very troublesome to handle. Incidentally, liquid fuels may include small amounts of additives to make them burn more smoothly, make them easier to handle, or keep them from freezing up in space.]]></description>
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		<title>Monopropellants</title>
		<link>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/286/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/286/#comments</comments>
		<pubDate>Mon, 17 May 2010 20:13:40 +0000</pubDate>
		<dc:creator>admin</dc:creator>
				<category><![CDATA[Chemical]]></category>

		<guid isPermaLink="false">http://www.spacebuild.net/s1/?p=286</guid>
		<description><![CDATA[The most common monopropellant in use is hydrazine. It is passes through a catalyst bed, where it decomposes into nitrogen and ammonia and delivers a specific impulse of about 230 lbf-s/lbm. Propulsion systems of this sort are well suited to pulsed operations of short duration, such as small spacecraft attitude control. (Adams, 1994) NASA is also developing new monopropellant systems to replace the current hydrazine monopropellant systems. The monopropellants under consideration are environmentally friendly, have a higher density, and have better thermal characteristics than hydrazine. The near-term goal is to improve mission performance and greatly reduce ground operations costs. For the far-term, a very high performance (high specific impulse) system is being sought. The key to this goal is the development of a high-temperature catalyst; research in this area is underway. For small spacecraft, several chemical propulsion technologies are being explored. Examples include: A warm gas propulsion system that uses a mixture of hydrogen, oxygen, and an inert gas (nitrogen or helium) and that offers a high specific impulse alternative to cold gas systems with a minimal increase in complexity Exothermic decomposing solid and hybrid systems, which offer the high density and simplicity of solid propellants for low-thrust, quick-response applications [...]]]></description>
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		<item>
		<title>Advanced Chemical Propulsion</title>
		<link>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/284/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/chemical-propulsion/284/#comments</comments>
		<pubDate>Sat, 17 Apr 2010 20:12:04 +0000</pubDate>
		<dc:creator>admin</dc:creator>
				<category><![CDATA[Chemical]]></category>

		<guid isPermaLink="false">http://www.spacebuild.net/s1/?p=284</guid>
		<description><![CDATA[Since we have already developed many different types of chemically-fueled propulsion systems, one might wonder why we need to advance these technologies. Historically, there has been a demand for improvements in many areas, such as safety, reduced mass, and of course increased specific impulse (Isp). Modern chemical propulsion systems utilize from one to three propellants and sometimes include exotic compounds.]]></description>
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