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"When you think about it, space travel requires an energy-efficient approach, especially if you&amp;#039;re going to make it to another planet. What green technologies are essential for space travel?"^^<http://www.w3.org/2001/XMLSchema#string>
<http://science.howstuffworks.com/environmental/green-science/5-green-technologies-for-interplanetary-space-travel3.htm>