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	<title>SpaceBuild &#187; Propulsion</title>
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	<description>Spacecraft technology</description>
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		<title>Gravity Propulsion</title>
		<link>http://www.spacebuild.net/s1/propulsion/gravity-propulsion/56/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/gravity-propulsion/56/#comments</comments>
		<pubDate>Fri, 07 Aug 2009 12:11:25 +0000</pubDate>
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				<category><![CDATA[Gravity]]></category>
		<category><![CDATA[gravity]]></category>
		<category><![CDATA[Propulsion]]></category>

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		<description><![CDATA[Gravity-Assisted In the early 1960s, a graduate student named Michael Minovitch working at JPL developed a way to use a planet&#8217;s gravitation as a method of propulsion. Gravity-assisted maneuvers work by transferring angular momentum from an orbiting planet to a passing spacecraft. A spacecraft&#8217;s trajectory is adjusted so that it will make a fairly close fly-by of a planet. As the spacecraft approaches the planet, the planet&#8217;s gravitational influence greatly accelerates the spacecraft in its orbit. Since momentum must be conserved, the planet slows in its orbit by a tiny amount. Gravity assists can be also used to decelerate a spacecraft, by flying in front of a body in its orbit, donating some of the spacecraft&#8217;s angular momentum to the body. When the Galileo spacecraft arrived at Jupiter, passing close in front of Io in its orbit, Galileo experienced deceleration, helping it achieve Jupiter orbit insertion The spacecraft Voyager 2 toured the Jovian planets (Jupiter, Saturn, Uranus, and Neptune). Its trajectory was carefully planned to utilize gravity assists to accelerate the craft toward its next destination, as shown in this illustration. This chart shows the increase in velocity (relative to the Sun) that the spacecraft gained as a result of [...]]]></description>
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		<title>Electric Propulsion</title>
		<link>http://www.spacebuild.net/s1/propulsion/electric-propulsion/20/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/electric-propulsion/20/#comments</comments>
		<pubDate>Tue, 14 Jul 2009 20:42:29 +0000</pubDate>
		<dc:creator>admin</dc:creator>
				<category><![CDATA[Electric]]></category>
		<category><![CDATA[electric]]></category>
		<category><![CDATA[Propulsion]]></category>

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		<description><![CDATA[Electric (Ion) Propulsion Electric propulsion works by using electrical energy to accelerate a propellant to much higher velocities than is possible using chemical reactions. The most common propellant used in ion engines is xenon. Early experimental ion engines used mercury and caesium, but they proved hard to work with. At room temperature, mercury is liquid and caesium is solid; they both must be heated first to turn them into a gas. There is a risk that as the mercury or caesium exhaust cools, many of the atoms would condense on the exterior surface of the spacecraft, thus contaminating instruments and solar cells. Research is now concentrated on xenon, which is as a cleaner and simpler fuel for use in ion engines. While current ion propulsion systems use solar panels to create the required electricity, there are plans for nuclear-powered ion systems. These would be of great use in exploring the outer solar system, where solar power is no longer efficient. Thrusters As stated above, ion propulsion involves ionising a gas to propel a craft. Instead of a spacecraft being propelled with standard chemicals, the gas xenon is given an electrical charge, or ionised. It is then electrically accelerated to a [...]]]></description>
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		<title>Solid Fuel Propulsion</title>
		<link>http://www.spacebuild.net/s1/propulsion/solid-fuel-propulsion/16/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/solid-fuel-propulsion/16/#comments</comments>
		<pubDate>Tue, 14 Jul 2009 17:44:23 +0000</pubDate>
		<dc:creator>admin</dc:creator>
				<category><![CDATA[Solid Fuel]]></category>
		<category><![CDATA[Propulsion]]></category>
		<category><![CDATA[solid fuel]]></category>

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		<description><![CDATA[Solid Fuel Solid-fuel rocket engines were the first engines created by man. They were invented by the Chinese in the 13th century and have been widely used since then. The &#8220;rocket&#8217;s red glare&#8221; in the American National Anthem, which was written in the early 1800&#8242;s, refers to the small solid-fuel rockets that were used to deliver bombs and incendiary devices during the War of 1812. The creation of solid-fuel rocket engines is fairly simple. They are made up of solid (dry) chemicals that, when ignited, burn very rapidly but will not explode. The exhaust gasses are directed through a nozzle that helps control and direct the gasses, providing accurate and even thrust. Although not generally used for interplanetary propulsion, solid chemical fuels are used in solid-rocket motors. Since solid-rocket motors cannot be throttled (turned off and on at will), they are of little use as a primary propulsion system for interplanetary missions. Solid-rocket motors are typically used in booster applications, to assist a spacecraft in lifting off from the Earth&#8217;s surface. Currently, the most visible example of solid-rocket motors can be seen on NASA&#8217;s space shuttle. The two white solid-rocket boosters (SRBs) are mounted to either side of the orange [...]]]></description>
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		<title>Solar Propulsion</title>
		<link>http://www.spacebuild.net/s1/propulsion/solar-propulsion/14/</link>
		<comments>http://www.spacebuild.net/s1/propulsion/solar-propulsion/14/#comments</comments>
		<pubDate>Tue, 14 Jul 2009 17:42:30 +0000</pubDate>
		<dc:creator>admin</dc:creator>
				<category><![CDATA[Solar]]></category>
		<category><![CDATA[Propulsion]]></category>
		<category><![CDATA[solar]]></category>

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		<description><![CDATA[Solar Propulsion Interplanetary Solar Sails A solar sail is a spacecraft that has an immense, lightweight mirror attached to it. It derives its propulsion by being pushed by light reflecting off of the mirror, instead of traditional rocket engines. The light used could be supplied by sunlight or lasers placed in orbit. Sunlight exerts a very gentle force. There are two identified ways to deploy a sail and keep it rigid. One is to use a deployment frame to maintain the sail shape, with the advantag that shape and position of the sail can be controlled, but at teh expense of having to deploy a large structure. the other method is to use centrifugal force to both deploy and maintain the sail structure through keeping it spinning. The power of sunlight in space at Earth&#8217;s distance from the sun is between 1.3-1.4 kilowatts per square meter. When you divide 1.4 kilowatts by the speed of light, about 300 million meters per second, the result is very small. A square mirror 1 kilometre on a side would only feel about 9 Newton or 2 pounds of force. Fortunately, space is very empty and clean compared to Earth, so there is plenty [...]]]></description>
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